The PAGEMAP_SCAN ioctl returns information regarding page table entries.
It is more efficient compared to reading pagemap files. CRIU can start
to utilize this ioctl, but it needs info about soft-dirty bits to track
memory changes.
We are aware of a new method for tracking memory changes implemented in
the PAGEMAP_SCAN ioctl. For CRIU, the primary advantage of this method
is its usability by unprivileged users. However, it is not feasible to
transparently replace the soft-dirty tracker with the new one. The main
problem here is userfault descriptors that have to be preserved between
pre-dump iterations. It means criu continues supporting the soft-dirty
method to avoid breakage for current users. The new method will be
implemented as a separate feature.
Cc: Muhammad Usama Anjum <[email protected]>
Cc: Michał Mirosław <[email protected]>
Signed-off-by: Andrei Vagin <[email protected]>
---
fs/proc/task_mmu.c | 13 ++++++++++++-
include/uapi/linux/fs.h | 1 +
2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ef2eb12906da..cefa676bd33b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1761,7 +1761,7 @@ static int pagemap_release(struct inode *inode, struct file *file)
#define PM_SCAN_CATEGORIES (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | \
PAGE_IS_FILE | PAGE_IS_PRESENT | \
PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \
- PAGE_IS_HUGE)
+ PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY)
#define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
struct pagemap_scan_private {
@@ -1853,12 +1853,16 @@ static unsigned long pagemap_thp_category(struct pagemap_scan_private *p,
if (is_zero_pfn(pmd_pfn(pmd)))
categories |= PAGE_IS_PFNZERO;
+ if (pmd_soft_dirty(pmd))
+ categories |= PAGE_IS_SOFT_DIRTY;
} else if (is_swap_pmd(pmd)) {
swp_entry_t swp;
categories |= PAGE_IS_SWAPPED;
if (!pmd_swp_uffd_wp(pmd))
categories |= PAGE_IS_WRITTEN;
+ if (pmd_swp_soft_dirty(pmd))
+ categories |= PAGE_IS_SOFT_DIRTY;
if (p->masks_of_interest & PAGE_IS_FILE) {
swp = pmd_to_swp_entry(pmd);
@@ -1905,10 +1909,14 @@ static unsigned long pagemap_hugetlb_category(pte_t pte)
categories |= PAGE_IS_FILE;
if (is_zero_pfn(pte_pfn(pte)))
categories |= PAGE_IS_PFNZERO;
+ if (pte_soft_dirty(pte))
+ categories |= PAGE_IS_SOFT_DIRTY;
} else if (is_swap_pte(pte)) {
categories |= PAGE_IS_SWAPPED;
if (!pte_swp_uffd_wp_any(pte))
categories |= PAGE_IS_WRITTEN;
+ if (pte_swp_soft_dirty(pte))
+ categories |= PAGE_IS_SOFT_DIRTY;
}
return categories;
@@ -1991,6 +1999,9 @@ static int pagemap_scan_test_walk(unsigned long start, unsigned long end,
if (vma->vm_flags & VM_PFNMAP)
return 1;
+ if (vma->vm_flags & VM_SOFTDIRTY)
+ vma_category |= PAGE_IS_SOFT_DIRTY;
+
if (!pagemap_scan_is_interesting_vma(vma_category, p))
return 1;
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index da43810b7485..48ad69f7722e 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -316,6 +316,7 @@ typedef int __bitwise __kernel_rwf_t;
#define PAGE_IS_SWAPPED (1 << 4)
#define PAGE_IS_PFNZERO (1 << 5)
#define PAGE_IS_HUGE (1 << 6)
+#define PAGE_IS_SOFT_DIRTY (1 << 7)
/*
* struct page_region - Page region with flags
--
2.42.0.869.gea05f2083d-goog
On 11/2/23 10:33 PM, Andrei Vagin wrote:
> The PAGEMAP_SCAN ioctl returns information regarding page table entries.
> It is more efficient compared to reading pagemap files. CRIU can start
> to utilize this ioctl, but it needs info about soft-dirty bits to track
> memory changes.
>
> We are aware of a new method for tracking memory changes implemented in
> the PAGEMAP_SCAN ioctl. For CRIU, the primary advantage of this method
> is its usability by unprivileged users. However, it is not feasible to
> transparently replace the soft-dirty tracker with the new one. The main
> problem here is userfault descriptors that have to be preserved between
> pre-dump iterations. It means criu continues supporting the soft-dirty
> method to avoid breakage for current users. The new method will be
> implemented as a separate feature.
>
> Cc: Muhammad Usama Anjum <[email protected]>
> Cc: Michał Mirosław <[email protected]>
> Signed-off-by: Andrei Vagin <[email protected]>
> ---
> fs/proc/task_mmu.c | 13 ++++++++++++-
> include/uapi/linux/fs.h | 1 +
> 2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index ef2eb12906da..cefa676bd33b 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1761,7 +1761,7 @@ static int pagemap_release(struct inode *inode, struct file *file)
> #define PM_SCAN_CATEGORIES (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | \
> PAGE_IS_FILE | PAGE_IS_PRESENT | \
> PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \
> - PAGE_IS_HUGE)
> + PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY)
> #define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
>
> struct pagemap_scan_private {
> @@ -1853,12 +1853,16 @@ static unsigned long pagemap_thp_category(struct pagemap_scan_private *p,
Probably missed the pagemap_page_category() for normal pages. Add
PAGE_IS_SOFT_DIRTY support for normal pages in pagemap_page_category() just
like pagemap_thp_category().
tools/testing/selftests/mm/soft-dirty.c can be updated to test if we are
getting the exactly same data from the ioctl.
>
> if (is_zero_pfn(pmd_pfn(pmd)))
> categories |= PAGE_IS_PFNZERO;
> + if (pmd_soft_dirty(pmd))
> + categories |= PAGE_IS_SOFT_DIRTY;
> } else if (is_swap_pmd(pmd)) {
> swp_entry_t swp;
>
> categories |= PAGE_IS_SWAPPED;
> if (!pmd_swp_uffd_wp(pmd))
> categories |= PAGE_IS_WRITTEN;
> + if (pmd_swp_soft_dirty(pmd))
> + categories |= PAGE_IS_SOFT_DIRTY;
>
> if (p->masks_of_interest & PAGE_IS_FILE) {
> swp = pmd_to_swp_entry(pmd);
> @@ -1905,10 +1909,14 @@ static unsigned long pagemap_hugetlb_category(pte_t pte)
> categories |= PAGE_IS_FILE;
> if (is_zero_pfn(pte_pfn(pte)))
> categories |= PAGE_IS_PFNZERO;
> + if (pte_soft_dirty(pte))
> + categories |= PAGE_IS_SOFT_DIRTY;
> } else if (is_swap_pte(pte)) {
> categories |= PAGE_IS_SWAPPED;
> if (!pte_swp_uffd_wp_any(pte))
> categories |= PAGE_IS_WRITTEN;
> + if (pte_swp_soft_dirty(pte))
> + categories |= PAGE_IS_SOFT_DIRTY;
> }
>
> return categories;
> @@ -1991,6 +1999,9 @@ static int pagemap_scan_test_walk(unsigned long start, unsigned long end,
> if (vma->vm_flags & VM_PFNMAP)
> return 1;
>
> + if (vma->vm_flags & VM_SOFTDIRTY)
> + vma_category |= PAGE_IS_SOFT_DIRTY;
> +
> if (!pagemap_scan_is_interesting_vma(vma_category, p))
> return 1;
>
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index da43810b7485..48ad69f7722e 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
Add this identical change in tools/include/uapi/linux/fs.h as well.
> @@ -316,6 +316,7 @@ typedef int __bitwise __kernel_rwf_t;
> #define PAGE_IS_SWAPPED (1 << 4)
> #define PAGE_IS_PFNZERO (1 << 5)
> #define PAGE_IS_HUGE (1 << 6)
> +#define PAGE_IS_SOFT_DIRTY (1 << 7)
Maybe one or couple of lines about it in the pagemap.rst.
>
> /*
> * struct page_region - Page region with flags
--
BR,
Muhammad Usama Anjum