This series makes hugetlb_optimize_vmemmap compatible with memmap_on_memory
and is based on mm-stable. The reason refers to the patch 2's commit log.
v4:
- Fix compiling error when CONFIG_MEMORY_HOTPLUG is disabled reported by kernel test robot.
- Fix a bug when memory_block_size_bytes() is not equal to section size.
v3:
- Switch complicated enumeration magic (David).
- Introduce PageVmemmapSelfHosted to make both parameters compatible (David and Oscar).
v2:
- Fix compile error when !CONFIG_ZONE_DEVICE reported by kernel test robot.
Muchun Song (2):
mm: memory_hotplug: enumerate all supported section flags
mm: memory_hotplug: make hugetlb_optimize_vmemmap compatible with
memmap_on_memory
Documentation/admin-guide/kernel-parameters.txt | 22 +++++------
Documentation/admin-guide/sysctl/vm.rst | 5 +--
include/linux/memory_hotplug.h | 9 -----
include/linux/mmzone.h | 44 ++++++++++++++++-----
include/linux/page-flags.h | 11 ++++++
mm/hugetlb_vmemmap.c | 52 +++++++++++++++++++++----
mm/memory_hotplug.c | 33 ++++++++--------
mm/sparse.c | 2 +-
8 files changed, 121 insertions(+), 57 deletions(-)
--
2.11.0
For now, the feature of hugetlb_free_vmemmap is not compatible with the
feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap
takes precedence over memory_hotplug.memmap_on_memory. However, someone
wants to make memory_hotplug.memmap_on_memory takes precedence over
hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
succeed memory hotplug in close-to-OOM situations. So the decision
of making hugetlb_free_vmemmap take precedence is not wise and elegant.
The proper approach is to have hugetlb_vmemmap.c do the check whether
the section which the HugeTLB pages belong to can be optimized. If
the section's vmemmap pages are allocated from the added memory block
itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap,
otherwise, do the optimization. Then both kernel parameters are
compatible. So this patch introduces VmemmapSelfHosted to mask any
non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag
to detect if a vmemmap page can be optimized.
Signed-off-by: Muchun Song <[email protected]>
Co-developed-by: Oscar Salvador <[email protected]>
Signed-off-by: Oscar Salvador <[email protected]>
---
Documentation/admin-guide/kernel-parameters.txt | 22 +++++------
Documentation/admin-guide/sysctl/vm.rst | 5 +--
include/linux/memory_hotplug.h | 9 -----
include/linux/page-flags.h | 11 ++++++
mm/hugetlb_vmemmap.c | 52 +++++++++++++++++++++----
mm/memory_hotplug.c | 27 ++++++-------
6 files changed, 79 insertions(+), 47 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 8090130b544b..d740e2ed0e61 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1722,9 +1722,11 @@
Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
the default is on.
- This is not compatible with memory_hotplug.memmap_on_memory.
- If both parameters are enabled, hugetlb_free_vmemmap takes
- precedence over memory_hotplug.memmap_on_memory.
+ Note that the vmemmap pages may be allocated from the added
+ memory block itself when memory_hotplug.memmap_on_memory is
+ enabled, those vmemmap pages cannot be optimized even if this
+ feature is enabled. Other vmemmap pages not allocated from
+ the added memory block itself do not be affected.
hung_task_panic=
[KNL] Should the hung task detector generate panics.
@@ -3069,10 +3071,12 @@
[KNL,X86,ARM] Boolean flag to enable this feature.
Format: {on | off (default)}
When enabled, runtime hotplugged memory will
- allocate its internal metadata (struct pages)
- from the hotadded memory which will allow to
- hotadd a lot of memory without requiring
- additional memory to do so.
+ allocate its internal metadata (struct pages,
+ those vmemmap pages cannot be optimized even
+ if hugetlb_free_vmemmap is enabled) from the
+ hotadded memory which will allow to hotadd a
+ lot of memory without requiring additional
+ memory to do so.
This feature is disabled by default because it
has some implication on large (e.g. GB)
allocations in some configurations (e.g. small
@@ -3082,10 +3086,6 @@
Note that even when enabled, there are a few cases where
the feature is not effective.
- This is not compatible with hugetlb_free_vmemmap. If
- both parameters are enabled, hugetlb_free_vmemmap takes
- precedence over memory_hotplug.memmap_on_memory.
-
memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
Format: <integer>
default : 0 <disable>
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 5c9aa171a0d3..d7374a1e8ac9 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst
hugetlb_optimize_vmemmap
========================
-This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter)
-is configured or the size of 'struct page' (a structure defined in
-include/linux/mm_types.h) is not power of two (an unusual system config could
+This knob is not available when the size of 'struct page' (a structure defined
+in include/linux/mm_types.h) is not power of two (an unusual system config could
result in this).
Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 20d7edf62a6a..e0b2209ab71c 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -351,13 +351,4 @@ void arch_remove_linear_mapping(u64 start, u64 size);
extern bool mhp_supports_memmap_on_memory(unsigned long size);
#endif /* CONFIG_MEMORY_HOTPLUG */
-#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
-bool mhp_memmap_on_memory(void);
-#else
-static inline bool mhp_memmap_on_memory(void)
-{
- return false;
-}
-#endif
-
#endif /* __LINUX_MEMORY_HOTPLUG_H */
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e66f7aa3191d..2aa5dcbfe468 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -193,6 +193,11 @@ enum pageflags {
/* Only valid for buddy pages. Used to track pages that are reported */
PG_reported = PG_uptodate,
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+ /* For self-hosted memmap pages */
+ PG_vmemmap_self_hosted = PG_owner_priv_1,
+#endif
};
#define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1)
@@ -628,6 +633,12 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison)
*/
__PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
+#ifdef CONFIG_MEMORY_HOTPLUG
+PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY)
+#else
+PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
+#endif
+
/*
* On an anonymous page mapped into a user virtual memory area,
* page->mapping points to its anon_vma, not to a struct address_space;
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 1089ea8a9c98..73bfbb47f6a4 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -10,7 +10,7 @@
*/
#define pr_fmt(fmt) "HugeTLB: " fmt
-#include <linux/memory_hotplug.h>
+#include <linux/memory.h>
#include "hugetlb_vmemmap.h"
/*
@@ -97,18 +97,54 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
return ret;
}
+static unsigned int vmemmap_optimizable_pages(struct hstate *h,
+ struct page *head)
+{
+ if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
+ return 0;
+
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
+ unsigned long pfn = page_to_pfn(head);
+
+ /*
+ * Due to HugeTLB alignment requirements and the vmemmap pages
+ * being at the start of the hotplugged memory region in
+ * memory_hotplug.memmap_on_memory case. Checking the first
+ * vmemmap page's vmemmap if it is marked as VmemmapSelfHosted
+ * is sufficient.
+ *
+ * [ hotplugged memory ]
+ * [ section ][...][ section ]
+ * [ vmemmap ][ usable memory ]
+ * ^ | | |
+ * +---+ | |
+ * ^ | |
+ * +-------+ |
+ * ^ |
+ * +-------------------------------------------+
+ *
+ * Hotplugged memory block never has non-present sections, while
+ * boot memory block can have one or more. So pfn_valid() is
+ * used to filter out the non-present section which also cannot
+ * be memmap_on_memory.
+ */
+ pfn = ALIGN_DOWN(pfn, PHYS_PFN(memory_block_size_bytes()));
+ if (pfn_valid(pfn) && PageVmemmapSelfHosted(pfn_to_page(pfn)))
+ return 0;
+ }
+
+ return hugetlb_optimize_vmemmap_pages(h);
+}
+
void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
{
unsigned long vmemmap_addr = (unsigned long)head;
unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
- vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);
+ vmemmap_pages = vmemmap_optimizable_pages(h, head);
if (!vmemmap_pages)
return;
- if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
- return;
-
static_branch_inc(&hugetlb_optimize_vmemmap_key);
vmemmap_addr += RESERVE_VMEMMAP_SIZE;
@@ -199,10 +235,10 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = {
static __init int hugetlb_vmemmap_sysctls_init(void)
{
/*
- * If "memory_hotplug.memmap_on_memory" is enabled or "struct page"
- * crosses page boundaries, the vmemmap pages cannot be optimized.
+ * If "struct page" crosses page boundaries, the vmemmap pages cannot
+ * be optimized.
*/
- if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page)))
+ if (is_power_of_2(sizeof(struct page)))
register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
return 0;
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6662b86e9e64..3a59d4e97c03 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -43,30 +43,22 @@
#include "shuffle.h"
#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
-static int memmap_on_memory_set(const char *val, const struct kernel_param *kp)
-{
- if (hugetlb_optimize_vmemmap_enabled())
- return 0;
- return param_set_bool(val, kp);
-}
-
-static const struct kernel_param_ops memmap_on_memory_ops = {
- .flags = KERNEL_PARAM_OPS_FL_NOARG,
- .set = memmap_on_memory_set,
- .get = param_get_bool,
-};
-
/*
* memory_hotplug.memmap_on_memory parameter
*/
static bool memmap_on_memory __ro_after_init;
-module_param_cb(memmap_on_memory, &memmap_on_memory_ops, &memmap_on_memory, 0444);
+module_param(memmap_on_memory, bool, 0444);
MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
-bool mhp_memmap_on_memory(void)
+static inline bool mhp_memmap_on_memory(void)
{
return memmap_on_memory;
}
+#else
+static inline bool mhp_memmap_on_memory(void)
+{
+ return false;
+}
#endif
enum {
@@ -1035,7 +1027,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
struct zone *zone)
{
unsigned long end_pfn = pfn + nr_pages;
- int ret;
+ int ret, i;
ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
if (ret)
@@ -1043,6 +1035,9 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE);
+ for (i = 0; i < nr_pages; i++)
+ SetPageVmemmapSelfHosted(pfn_to_page(pfn + i));
+
/*
* It might be that the vmemmap_pages fully span sections. If that is
* the case, mark those sections online here as otherwise they will be
--
2.11.0
On 20.06.22 09:22, Muchun Song wrote:
> On Sun, Jun 19, 2022 at 09:38:51PM +0800, Muchun Song wrote:
>> For now, the feature of hugetlb_free_vmemmap is not compatible with the
>> feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap
>> takes precedence over memory_hotplug.memmap_on_memory. However, someone
>> wants to make memory_hotplug.memmap_on_memory takes precedence over
>> hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
>> succeed memory hotplug in close-to-OOM situations. So the decision
>> of making hugetlb_free_vmemmap take precedence is not wise and elegant.
>> The proper approach is to have hugetlb_vmemmap.c do the check whether
>> the section which the HugeTLB pages belong to can be optimized. If
>> the section's vmemmap pages are allocated from the added memory block
>> itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap,
>> otherwise, do the optimization. Then both kernel parameters are
>> compatible. So this patch introduces VmemmapSelfHosted to mask any
>> non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag
>> to detect if a vmemmap page can be optimized.
>>
>> Signed-off-by: Muchun Song <[email protected]>
>> Co-developed-by: Oscar Salvador <[email protected]>
>> Signed-off-by: Oscar Salvador <[email protected]>
>> ---
>> Documentation/admin-guide/kernel-parameters.txt | 22 +++++------
>> Documentation/admin-guide/sysctl/vm.rst | 5 +--
>> include/linux/memory_hotplug.h | 9 -----
>> include/linux/page-flags.h | 11 ++++++
>> mm/hugetlb_vmemmap.c | 52 +++++++++++++++++++++----
>> mm/memory_hotplug.c | 27 ++++++-------
>> 6 files changed, 79 insertions(+), 47 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 8090130b544b..d740e2ed0e61 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1722,9 +1722,11 @@
>> Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
>> the default is on.
>>
>> - This is not compatible with memory_hotplug.memmap_on_memory.
>> - If both parameters are enabled, hugetlb_free_vmemmap takes
>> - precedence over memory_hotplug.memmap_on_memory.
>> + Note that the vmemmap pages may be allocated from the added
>> + memory block itself when memory_hotplug.memmap_on_memory is
>> + enabled, those vmemmap pages cannot be optimized even if this
>> + feature is enabled. Other vmemmap pages not allocated from
>> + the added memory block itself do not be affected.
>>
>> hung_task_panic=
>> [KNL] Should the hung task detector generate panics.
>> @@ -3069,10 +3071,12 @@
>> [KNL,X86,ARM] Boolean flag to enable this feature.
>> Format: {on | off (default)}
>> When enabled, runtime hotplugged memory will
>> - allocate its internal metadata (struct pages)
>> - from the hotadded memory which will allow to
>> - hotadd a lot of memory without requiring
>> - additional memory to do so.
>> + allocate its internal metadata (struct pages,
>> + those vmemmap pages cannot be optimized even
>> + if hugetlb_free_vmemmap is enabled) from the
>> + hotadded memory which will allow to hotadd a
>> + lot of memory without requiring additional
>> + memory to do so.
>> This feature is disabled by default because it
>> has some implication on large (e.g. GB)
>> allocations in some configurations (e.g. small
>> @@ -3082,10 +3086,6 @@
>> Note that even when enabled, there are a few cases where
>> the feature is not effective.
>>
>> - This is not compatible with hugetlb_free_vmemmap. If
>> - both parameters are enabled, hugetlb_free_vmemmap takes
>> - precedence over memory_hotplug.memmap_on_memory.
>> -
>> memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
>> Format: <integer>
>> default : 0 <disable>
>> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
>> index 5c9aa171a0d3..d7374a1e8ac9 100644
>> --- a/Documentation/admin-guide/sysctl/vm.rst
>> +++ b/Documentation/admin-guide/sysctl/vm.rst
>> @@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst
>> hugetlb_optimize_vmemmap
>> ========================
>>
>> -This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter)
>> -is configured or the size of 'struct page' (a structure defined in
>> -include/linux/mm_types.h) is not power of two (an unusual system config could
>> +This knob is not available when the size of 'struct page' (a structure defined
>> +in include/linux/mm_types.h) is not power of two (an unusual system config could
>> result in this).
>>
>> Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
>> index 20d7edf62a6a..e0b2209ab71c 100644
>> --- a/include/linux/memory_hotplug.h
>> +++ b/include/linux/memory_hotplug.h
>> @@ -351,13 +351,4 @@ void arch_remove_linear_mapping(u64 start, u64 size);
>> extern bool mhp_supports_memmap_on_memory(unsigned long size);
>> #endif /* CONFIG_MEMORY_HOTPLUG */
>>
>> -#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
>> -bool mhp_memmap_on_memory(void);
>> -#else
>> -static inline bool mhp_memmap_on_memory(void)
>> -{
>> - return false;
>> -}
>> -#endif
>> -
>> #endif /* __LINUX_MEMORY_HOTPLUG_H */
>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>> index e66f7aa3191d..2aa5dcbfe468 100644
>> --- a/include/linux/page-flags.h
>> +++ b/include/linux/page-flags.h
>> @@ -193,6 +193,11 @@ enum pageflags {
>>
>> /* Only valid for buddy pages. Used to track pages that are reported */
>> PG_reported = PG_uptodate,
>> +
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> + /* For self-hosted memmap pages */
>> + PG_vmemmap_self_hosted = PG_owner_priv_1,
>> +#endif
>> };
>>
>> #define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1)
>> @@ -628,6 +633,12 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison)
>> */
>> __PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
>>
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY)
>> +#else
>> +PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
>> +#endif
>> +
>> /*
>> * On an anonymous page mapped into a user virtual memory area,
>> * page->mapping points to its anon_vma, not to a struct address_space;
>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
>> index 1089ea8a9c98..73bfbb47f6a4 100644
>> --- a/mm/hugetlb_vmemmap.c
>> +++ b/mm/hugetlb_vmemmap.c
>> @@ -10,7 +10,7 @@
>> */
>> #define pr_fmt(fmt) "HugeTLB: " fmt
>>
>> -#include <linux/memory_hotplug.h>
>> +#include <linux/memory.h>
>> #include "hugetlb_vmemmap.h"
>>
>> /*
>> @@ -97,18 +97,54 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
>> return ret;
>> }
>>
>> +static unsigned int vmemmap_optimizable_pages(struct hstate *h,
>> + struct page *head)
>> +{
>> + if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
>> + return 0;
>> +
>> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
>> + unsigned long pfn = page_to_pfn(head);
>> +
>> + /*
>> + * Due to HugeTLB alignment requirements and the vmemmap pages
>> + * being at the start of the hotplugged memory region in
>> + * memory_hotplug.memmap_on_memory case. Checking the first
>> + * vmemmap page's vmemmap if it is marked as VmemmapSelfHosted
>> + * is sufficient.
>> + *
>> + * [ hotplugged memory ]
>> + * [ section ][...][ section ]
>> + * [ vmemmap ][ usable memory ]
>> + * ^ | | |
>> + * +---+ | |
>> + * ^ | |
>> + * +-------+ |
>> + * ^ |
>> + * +-------------------------------------------+
>> + *
>> + * Hotplugged memory block never has non-present sections, while
>> + * boot memory block can have one or more. So pfn_valid() is
>> + * used to filter out the non-present section which also cannot
>> + * be memmap_on_memory.
>> + */
>> + pfn = ALIGN_DOWN(pfn, PHYS_PFN(memory_block_size_bytes()));
>> + if (pfn_valid(pfn) && PageVmemmapSelfHosted(pfn_to_page(pfn)))
>
> Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's
> vmemmap page is not always reliable. Since we reused PG_owner_priv_1
> as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's
> vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1.
> So this check can be false-positive. Maybe the following code snippet is
> the solution.
How could that happen for pages used for backing a vmemmap?
>
> Any thoughts? Oscar or David.
First of all, I think you should really avoid using
memory_block_size_bytes(); when using memory_block_size_bytes(), you
wouldn't need PageVmemmapSelfHosted(), you can just check if the vmemmap
of the page is itself. But I think we should try making this independent
of the memory block size.
If virt_to_page(page) doesn't work, maybe just traverse the direct map
to find the page backing page directly?
--
Thanks,
David / dhildenb
On Sun, Jun 19, 2022 at 09:38:51PM +0800, Muchun Song wrote:
> For now, the feature of hugetlb_free_vmemmap is not compatible with the
> feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap
> takes precedence over memory_hotplug.memmap_on_memory. However, someone
> wants to make memory_hotplug.memmap_on_memory takes precedence over
> hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
> succeed memory hotplug in close-to-OOM situations. So the decision
> of making hugetlb_free_vmemmap take precedence is not wise and elegant.
> The proper approach is to have hugetlb_vmemmap.c do the check whether
> the section which the HugeTLB pages belong to can be optimized. If
> the section's vmemmap pages are allocated from the added memory block
> itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap,
> otherwise, do the optimization. Then both kernel parameters are
> compatible. So this patch introduces VmemmapSelfHosted to mask any
> non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag
> to detect if a vmemmap page can be optimized.
>
> Signed-off-by: Muchun Song <[email protected]>
> Co-developed-by: Oscar Salvador <[email protected]>
> Signed-off-by: Oscar Salvador <[email protected]>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 22 +++++------
> Documentation/admin-guide/sysctl/vm.rst | 5 +--
> include/linux/memory_hotplug.h | 9 -----
> include/linux/page-flags.h | 11 ++++++
> mm/hugetlb_vmemmap.c | 52 +++++++++++++++++++++----
> mm/memory_hotplug.c | 27 ++++++-------
> 6 files changed, 79 insertions(+), 47 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 8090130b544b..d740e2ed0e61 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1722,9 +1722,11 @@
> Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
> the default is on.
>
> - This is not compatible with memory_hotplug.memmap_on_memory.
> - If both parameters are enabled, hugetlb_free_vmemmap takes
> - precedence over memory_hotplug.memmap_on_memory.
> + Note that the vmemmap pages may be allocated from the added
> + memory block itself when memory_hotplug.memmap_on_memory is
> + enabled, those vmemmap pages cannot be optimized even if this
> + feature is enabled. Other vmemmap pages not allocated from
> + the added memory block itself do not be affected.
>
> hung_task_panic=
> [KNL] Should the hung task detector generate panics.
> @@ -3069,10 +3071,12 @@
> [KNL,X86,ARM] Boolean flag to enable this feature.
> Format: {on | off (default)}
> When enabled, runtime hotplugged memory will
> - allocate its internal metadata (struct pages)
> - from the hotadded memory which will allow to
> - hotadd a lot of memory without requiring
> - additional memory to do so.
> + allocate its internal metadata (struct pages,
> + those vmemmap pages cannot be optimized even
> + if hugetlb_free_vmemmap is enabled) from the
> + hotadded memory which will allow to hotadd a
> + lot of memory without requiring additional
> + memory to do so.
> This feature is disabled by default because it
> has some implication on large (e.g. GB)
> allocations in some configurations (e.g. small
> @@ -3082,10 +3086,6 @@
> Note that even when enabled, there are a few cases where
> the feature is not effective.
>
> - This is not compatible with hugetlb_free_vmemmap. If
> - both parameters are enabled, hugetlb_free_vmemmap takes
> - precedence over memory_hotplug.memmap_on_memory.
> -
> memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
> Format: <integer>
> default : 0 <disable>
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index 5c9aa171a0d3..d7374a1e8ac9 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst
> hugetlb_optimize_vmemmap
> ========================
>
> -This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter)
> -is configured or the size of 'struct page' (a structure defined in
> -include/linux/mm_types.h) is not power of two (an unusual system config could
> +This knob is not available when the size of 'struct page' (a structure defined
> +in include/linux/mm_types.h) is not power of two (an unusual system config could
> result in this).
>
> Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 20d7edf62a6a..e0b2209ab71c 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -351,13 +351,4 @@ void arch_remove_linear_mapping(u64 start, u64 size);
> extern bool mhp_supports_memmap_on_memory(unsigned long size);
> #endif /* CONFIG_MEMORY_HOTPLUG */
>
> -#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
> -bool mhp_memmap_on_memory(void);
> -#else
> -static inline bool mhp_memmap_on_memory(void)
> -{
> - return false;
> -}
> -#endif
> -
> #endif /* __LINUX_MEMORY_HOTPLUG_H */
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index e66f7aa3191d..2aa5dcbfe468 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -193,6 +193,11 @@ enum pageflags {
>
> /* Only valid for buddy pages. Used to track pages that are reported */
> PG_reported = PG_uptodate,
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> + /* For self-hosted memmap pages */
> + PG_vmemmap_self_hosted = PG_owner_priv_1,
> +#endif
> };
>
> #define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1)
> @@ -628,6 +633,12 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison)
> */
> __PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
>
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY)
> +#else
> +PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
> +#endif
> +
> /*
> * On an anonymous page mapped into a user virtual memory area,
> * page->mapping points to its anon_vma, not to a struct address_space;
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 1089ea8a9c98..73bfbb47f6a4 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -10,7 +10,7 @@
> */
> #define pr_fmt(fmt) "HugeTLB: " fmt
>
> -#include <linux/memory_hotplug.h>
> +#include <linux/memory.h>
> #include "hugetlb_vmemmap.h"
>
> /*
> @@ -97,18 +97,54 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
> return ret;
> }
>
> +static unsigned int vmemmap_optimizable_pages(struct hstate *h,
> + struct page *head)
> +{
> + if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
> + return 0;
> +
> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
> + unsigned long pfn = page_to_pfn(head);
> +
> + /*
> + * Due to HugeTLB alignment requirements and the vmemmap pages
> + * being at the start of the hotplugged memory region in
> + * memory_hotplug.memmap_on_memory case. Checking the first
> + * vmemmap page's vmemmap if it is marked as VmemmapSelfHosted
> + * is sufficient.
> + *
> + * [ hotplugged memory ]
> + * [ section ][...][ section ]
> + * [ vmemmap ][ usable memory ]
> + * ^ | | |
> + * +---+ | |
> + * ^ | |
> + * +-------+ |
> + * ^ |
> + * +-------------------------------------------+
> + *
> + * Hotplugged memory block never has non-present sections, while
> + * boot memory block can have one or more. So pfn_valid() is
> + * used to filter out the non-present section which also cannot
> + * be memmap_on_memory.
> + */
> + pfn = ALIGN_DOWN(pfn, PHYS_PFN(memory_block_size_bytes()));
> + if (pfn_valid(pfn) && PageVmemmapSelfHosted(pfn_to_page(pfn)))
Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's
vmemmap page is not always reliable. Since we reused PG_owner_priv_1
as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's
vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1.
So this check can be false-positive. Maybe the following code snippet is
the solution.
Any thoughts? Oscar or David.
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
+ pmd_t *pmdp, pmd;
+ struct page *vmemmap_page;
+ unsigned long vaddr = (unsigned long)head;
+
+ pmdp = pmd_off_k(vaddr);
+ /*
+ * The READ_ONCE() is used to stabilize *pmdp in a register or
+ * on the stack so that it will stop changing under the code.
+ */
+ pmd = READ_ONCE(*pmdp);
+ if (pmd_leaf(pmd))
+ vmemmap_page = pmd_page(pmd) + pte_index(vaddr);
+ else
+ vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));
+ /*
+ * Due to HugeTLB alignment requirements and the vmemmap pages
+ * being at the start of the hotplugged memory region in
+ * memory_hotplug.memmap_on_memory case. Checking any vmemmap
+ * page's vmemmap page if it is marked as VmemmapSelfHosted is
+ * sufficient.
+ *
+ * [ hotplugged memory ]
+ * [ section ][...][ section ]
+ * [ vmemmap ][ usable memory ]
+ * ^ | | |
+ * +---+ | |
+ * ^ | |
+ * +-------+ |
+ * ^ |
+ * +-------------------------------------------+
+ */
+ if (PageVmemmapSelfHosted(vmemmap_page))
+ return 0;
+ }
> + return 0;
> + }
> +
> + return hugetlb_optimize_vmemmap_pages(h);
> +}
> +
> void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
> {
> unsigned long vmemmap_addr = (unsigned long)head;
> unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
>
> - vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);
> + vmemmap_pages = vmemmap_optimizable_pages(h, head);
> if (!vmemmap_pages)
> return;
>
> - if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
> - return;
> -
> static_branch_inc(&hugetlb_optimize_vmemmap_key);
>
> vmemmap_addr += RESERVE_VMEMMAP_SIZE;
> @@ -199,10 +235,10 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = {
> static __init int hugetlb_vmemmap_sysctls_init(void)
> {
> /*
> - * If "memory_hotplug.memmap_on_memory" is enabled or "struct page"
> - * crosses page boundaries, the vmemmap pages cannot be optimized.
> + * If "struct page" crosses page boundaries, the vmemmap pages cannot
> + * be optimized.
> */
> - if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page)))
> + if (is_power_of_2(sizeof(struct page)))
> register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
>
> return 0;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6662b86e9e64..3a59d4e97c03 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -43,30 +43,22 @@
> #include "shuffle.h"
>
> #ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
> -static int memmap_on_memory_set(const char *val, const struct kernel_param *kp)
> -{
> - if (hugetlb_optimize_vmemmap_enabled())
> - return 0;
> - return param_set_bool(val, kp);
> -}
> -
> -static const struct kernel_param_ops memmap_on_memory_ops = {
> - .flags = KERNEL_PARAM_OPS_FL_NOARG,
> - .set = memmap_on_memory_set,
> - .get = param_get_bool,
> -};
> -
> /*
> * memory_hotplug.memmap_on_memory parameter
> */
> static bool memmap_on_memory __ro_after_init;
> -module_param_cb(memmap_on_memory, &memmap_on_memory_ops, &memmap_on_memory, 0444);
> +module_param(memmap_on_memory, bool, 0444);
> MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
>
> -bool mhp_memmap_on_memory(void)
> +static inline bool mhp_memmap_on_memory(void)
> {
> return memmap_on_memory;
> }
> +#else
> +static inline bool mhp_memmap_on_memory(void)
> +{
> + return false;
> +}
> #endif
>
> enum {
> @@ -1035,7 +1027,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
> struct zone *zone)
> {
> unsigned long end_pfn = pfn + nr_pages;
> - int ret;
> + int ret, i;
>
> ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
> if (ret)
> @@ -1043,6 +1035,9 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
>
> move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE);
>
> + for (i = 0; i < nr_pages; i++)
> + SetPageVmemmapSelfHosted(pfn_to_page(pfn + i));
> +
> /*
> * It might be that the vmemmap_pages fully span sections. If that is
> * the case, mark those sections online here as otherwise they will be
> --
> 2.11.0
>
>
On Mon, Jun 20, 2022 at 09:47:22AM +0200, David Hildenbrand wrote:
> On 20.06.22 09:22, Muchun Song wrote:
> > On Sun, Jun 19, 2022 at 09:38:51PM +0800, Muchun Song wrote:
> >> For now, the feature of hugetlb_free_vmemmap is not compatible with the
> >> feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap
> >> takes precedence over memory_hotplug.memmap_on_memory. However, someone
> >> wants to make memory_hotplug.memmap_on_memory takes precedence over
> >> hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
> >> succeed memory hotplug in close-to-OOM situations. So the decision
> >> of making hugetlb_free_vmemmap take precedence is not wise and elegant.
> >> The proper approach is to have hugetlb_vmemmap.c do the check whether
> >> the section which the HugeTLB pages belong to can be optimized. If
> >> the section's vmemmap pages are allocated from the added memory block
> >> itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap,
> >> otherwise, do the optimization. Then both kernel parameters are
> >> compatible. So this patch introduces VmemmapSelfHosted to mask any
> >> non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag
> >> to detect if a vmemmap page can be optimized.
> >>
> >> Signed-off-by: Muchun Song <[email protected]>
> >> Co-developed-by: Oscar Salvador <[email protected]>
> >> Signed-off-by: Oscar Salvador <[email protected]>
> >> ---
> >> Documentation/admin-guide/kernel-parameters.txt | 22 +++++------
> >> Documentation/admin-guide/sysctl/vm.rst | 5 +--
> >> include/linux/memory_hotplug.h | 9 -----
> >> include/linux/page-flags.h | 11 ++++++
> >> mm/hugetlb_vmemmap.c | 52 +++++++++++++++++++++----
> >> mm/memory_hotplug.c | 27 ++++++-------
> >> 6 files changed, 79 insertions(+), 47 deletions(-)
> >>
> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> >> index 8090130b544b..d740e2ed0e61 100644
> >> --- a/Documentation/admin-guide/kernel-parameters.txt
> >> +++ b/Documentation/admin-guide/kernel-parameters.txt
> >> @@ -1722,9 +1722,11 @@
> >> Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
> >> the default is on.
> >>
> >> - This is not compatible with memory_hotplug.memmap_on_memory.
> >> - If both parameters are enabled, hugetlb_free_vmemmap takes
> >> - precedence over memory_hotplug.memmap_on_memory.
> >> + Note that the vmemmap pages may be allocated from the added
> >> + memory block itself when memory_hotplug.memmap_on_memory is
> >> + enabled, those vmemmap pages cannot be optimized even if this
> >> + feature is enabled. Other vmemmap pages not allocated from
> >> + the added memory block itself do not be affected.
> >>
> >> hung_task_panic=
> >> [KNL] Should the hung task detector generate panics.
> >> @@ -3069,10 +3071,12 @@
> >> [KNL,X86,ARM] Boolean flag to enable this feature.
> >> Format: {on | off (default)}
> >> When enabled, runtime hotplugged memory will
> >> - allocate its internal metadata (struct pages)
> >> - from the hotadded memory which will allow to
> >> - hotadd a lot of memory without requiring
> >> - additional memory to do so.
> >> + allocate its internal metadata (struct pages,
> >> + those vmemmap pages cannot be optimized even
> >> + if hugetlb_free_vmemmap is enabled) from the
> >> + hotadded memory which will allow to hotadd a
> >> + lot of memory without requiring additional
> >> + memory to do so.
> >> This feature is disabled by default because it
> >> has some implication on large (e.g. GB)
> >> allocations in some configurations (e.g. small
> >> @@ -3082,10 +3086,6 @@
> >> Note that even when enabled, there are a few cases where
> >> the feature is not effective.
> >>
> >> - This is not compatible with hugetlb_free_vmemmap. If
> >> - both parameters are enabled, hugetlb_free_vmemmap takes
> >> - precedence over memory_hotplug.memmap_on_memory.
> >> -
> >> memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
> >> Format: <integer>
> >> default : 0 <disable>
> >> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> >> index 5c9aa171a0d3..d7374a1e8ac9 100644
> >> --- a/Documentation/admin-guide/sysctl/vm.rst
> >> +++ b/Documentation/admin-guide/sysctl/vm.rst
> >> @@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst
> >> hugetlb_optimize_vmemmap
> >> ========================
> >>
> >> -This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter)
> >> -is configured or the size of 'struct page' (a structure defined in
> >> -include/linux/mm_types.h) is not power of two (an unusual system config could
> >> +This knob is not available when the size of 'struct page' (a structure defined
> >> +in include/linux/mm_types.h) is not power of two (an unusual system config could
> >> result in this).
> >>
> >> Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
> >> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> >> index 20d7edf62a6a..e0b2209ab71c 100644
> >> --- a/include/linux/memory_hotplug.h
> >> +++ b/include/linux/memory_hotplug.h
> >> @@ -351,13 +351,4 @@ void arch_remove_linear_mapping(u64 start, u64 size);
> >> extern bool mhp_supports_memmap_on_memory(unsigned long size);
> >> #endif /* CONFIG_MEMORY_HOTPLUG */
> >>
> >> -#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
> >> -bool mhp_memmap_on_memory(void);
> >> -#else
> >> -static inline bool mhp_memmap_on_memory(void)
> >> -{
> >> - return false;
> >> -}
> >> -#endif
> >> -
> >> #endif /* __LINUX_MEMORY_HOTPLUG_H */
> >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> >> index e66f7aa3191d..2aa5dcbfe468 100644
> >> --- a/include/linux/page-flags.h
> >> +++ b/include/linux/page-flags.h
> >> @@ -193,6 +193,11 @@ enum pageflags {
> >>
> >> /* Only valid for buddy pages. Used to track pages that are reported */
> >> PG_reported = PG_uptodate,
> >> +
> >> +#ifdef CONFIG_MEMORY_HOTPLUG
> >> + /* For self-hosted memmap pages */
> >> + PG_vmemmap_self_hosted = PG_owner_priv_1,
> >> +#endif
> >> };
> >>
> >> #define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1)
> >> @@ -628,6 +633,12 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison)
> >> */
> >> __PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
> >>
> >> +#ifdef CONFIG_MEMORY_HOTPLUG
> >> +PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY)
> >> +#else
> >> +PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
> >> +#endif
> >> +
> >> /*
> >> * On an anonymous page mapped into a user virtual memory area,
> >> * page->mapping points to its anon_vma, not to a struct address_space;
> >> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> >> index 1089ea8a9c98..73bfbb47f6a4 100644
> >> --- a/mm/hugetlb_vmemmap.c
> >> +++ b/mm/hugetlb_vmemmap.c
> >> @@ -10,7 +10,7 @@
> >> */
> >> #define pr_fmt(fmt) "HugeTLB: " fmt
> >>
> >> -#include <linux/memory_hotplug.h>
> >> +#include <linux/memory.h>
> >> #include "hugetlb_vmemmap.h"
> >>
> >> /*
> >> @@ -97,18 +97,54 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
> >> return ret;
> >> }
> >>
> >> +static unsigned int vmemmap_optimizable_pages(struct hstate *h,
> >> + struct page *head)
> >> +{
> >> + if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
> >> + return 0;
> >> +
> >> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
> >> + unsigned long pfn = page_to_pfn(head);
> >> +
> >> + /*
> >> + * Due to HugeTLB alignment requirements and the vmemmap pages
> >> + * being at the start of the hotplugged memory region in
> >> + * memory_hotplug.memmap_on_memory case. Checking the first
> >> + * vmemmap page's vmemmap if it is marked as VmemmapSelfHosted
> >> + * is sufficient.
> >> + *
> >> + * [ hotplugged memory ]
> >> + * [ section ][...][ section ]
> >> + * [ vmemmap ][ usable memory ]
> >> + * ^ | | |
> >> + * +---+ | |
> >> + * ^ | |
> >> + * +-------+ |
> >> + * ^ |
> >> + * +-------------------------------------------+
> >> + *
> >> + * Hotplugged memory block never has non-present sections, while
> >> + * boot memory block can have one or more. So pfn_valid() is
> >> + * used to filter out the non-present section which also cannot
> >> + * be memmap_on_memory.
> >> + */
> >> + pfn = ALIGN_DOWN(pfn, PHYS_PFN(memory_block_size_bytes()));
> >> + if (pfn_valid(pfn) && PageVmemmapSelfHosted(pfn_to_page(pfn)))
> >
> > Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's
> > vmemmap page is not always reliable. Since we reused PG_owner_priv_1
> > as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's
> > vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1.
> > So this check can be false-positive. Maybe the following code snippet is
> > the solution.
>
> How could that happen for pages used for backing a vmemmap?
>
It cannot happen for memmap_on_memory case. Howwver, it can happen for other
cases. E.g. the 1st pfn (of boot memory block) whose vmemmap page may be flagged
as PG_owner_priv_1 (if PG_swapcache is set). Then, the check is false-positive.
> >
> > Any thoughts? Oscar or David.
>
> First of all, I think you should really avoid using
> memory_block_size_bytes(); when using memory_block_size_bytes(), you
> wouldn't need PageVmemmapSelfHosted(), you can just check if the vmemmap
> of the page is itself. But I think we should try making this independent
> of the memory block size.
>
Agree.
> If virt_to_page(page) doesn't work, maybe just traverse the direct map
> to find the page backing page directly?
>
Yeah, now I have tried to walk page tables to get the backing page.
I'll update a new version.
Thanks.
> --
> Thanks,
>
> David / dhildenb
>
>
On Mon, Jun 20, 2022 at 04:29:11PM +0800, Muchun Song wrote:
> > > Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's
> > > vmemmap page is not always reliable. Since we reused PG_owner_priv_1
> > > as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's
> > > vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1.
> > > So this check can be false-positive. Maybe the following code snippet is
> > > the solution.
> >
> > How could that happen for pages used for backing a vmemmap?
> >
>
> It cannot happen for memmap_on_memory case. Howwver, it can happen for other
> cases. E.g. the 1st pfn (of boot memory block) whose vmemmap page may be flagged
> as PG_owner_priv_1 (if PG_swapcache is set). Then, the check is false-positive.
If this can really happen, which I am not that sure tbh, maybe a way out would be
to just define a new page-type as we did in previous versions of memmap_on_memory.
In that way we would not for flags, but for its type.
But as I said, I am not entirely sure about the potential fallout of what you mention.
--
Oscar Salvador
SUSE Labs
On Mon, Jun 20, 2022 at 10:44:40AM +0200, Oscar Salvador wrote:
> On Mon, Jun 20, 2022 at 04:29:11PM +0800, Muchun Song wrote:
> > > > Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's
> > > > vmemmap page is not always reliable. Since we reused PG_owner_priv_1
> > > > as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's
> > > > vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1.
> > > > So this check can be false-positive. Maybe the following code snippet is
> > > > the solution.
> > >
> > > How could that happen for pages used for backing a vmemmap?
> > >
> >
> > It cannot happen for memmap_on_memory case. Howwver, it can happen for other
> > cases. E.g. the 1st pfn (of boot memory block) whose vmemmap page may be flagged
> > as PG_owner_priv_1 (if PG_swapcache is set). Then, the check is false-positive.
>
> If this can really happen, which I am not that sure tbh, maybe a way out would be
I need to clarify this only can be happened by using this approach implemented
in this patch.
For a boot memory block, the vemmmap pages are not slef-hosted. So the 1st pfn (of
this memory block) can be allocated to other users. e.g. an anonymous page with
PG_swapcache set. In this patch, ALIGN_DOWN(pfn, PHYS_PFN(memory_block_size_bytes()))
will located on this anonymous page, then the check is false-positive.
[ boot memory block ]
[ section ][...][ section ]
[ usable memory ]
> to just define a new page-type as we did in previous versions of memmap_on_memory.
> In that way we would not for flags, but for its type.
>
I think we do not need to introduced a new flag, we just make sure the page
passed to PageVmemmapSelfHosted() is a backing page for vmemmap. Then we
cannot incur false-positive. The feasible solution is walking page tables
to find a vmemmap page's backing page.
Thanks.
> But as I said, I am not entirely sure about the potential fallout of what you mention.
>
>
> --
> Oscar Salvador
> SUSE Labs
>
On 20.06.22 10:44, Oscar Salvador wrote:
> On Mon, Jun 20, 2022 at 04:29:11PM +0800, Muchun Song wrote:
>>>> Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's
>>>> vmemmap page is not always reliable. Since we reused PG_owner_priv_1
>>>> as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's
>>>> vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1.
>>>> So this check can be false-positive. Maybe the following code snippet is
>>>> the solution.
>>>
>>> How could that happen for pages used for backing a vmemmap?
>>>
>>
>> It cannot happen for memmap_on_memory case. Howwver, it can happen for other
>> cases. E.g. the 1st pfn (of boot memory block) whose vmemmap page may be flagged
>> as PG_owner_priv_1 (if PG_swapcache is set). Then, the check is false-positive.
>
> If this can really happen, which I am not that sure tbh, maybe a way out would be
> to just define a new page-type as we did in previous versions of memmap_on_memory.
> In that way we would not for flags, but for its type.
>
> But as I said, I am not entirely sure about the potential fallout of what you mention.
We are talking about the memmap of a page, who's page content is the
memmap of pages actually exposed to other users (file-backed, anonymous,
whatsoever).
In other words, while setting PG_swapcache on the memmap of a page
exposed to the user is possible, it shouldn't be possible for the memmap
of the page "hosting" these memmaps.
I know, it's confusing and I keep confusing myself. I tried creating a
picture and it doesn't really clarify the situation :D
--
Thanks,
David / dhildenb