LinuxLists.cc - [PATCH 1/6] mm: hugetlb_vmemmap: delete hugetlb_optimize_vmemmap

2022-06-13 06:37:24

Subject: [PATCH 1/6] mm: hugetlb_vmemmap: delete hugetlb_optimize_vmemmap_enabled()

The name hugetlb_optimize_vmemmap_enabled() a bit confusing as it tests
two conditions (enabled and pages in use). Instead of coming up to
an appropriate name, we could just delete it. There is already a
discussion about deleting it in thread [1].

There is only one user of hugetlb_optimize_vmemmap_enabled() outside of
hugetlb_vmemmap, that is flush_dcache_page() in arch/arm64/mm/flush.c.
However, it does not need to call hugetlb_optimize_vmemmap_enabled()
in flush_dcache_page() since HugeTLB pages are always fully mapped and
only head page will be set PG_dcache_clean meaning only head page's flag
may need to be cleared (see commit cf5a501d985b). So it is easy to
remove hugetlb_optimize_vmemmap_enabled().

Link: https://lore.kernel.org/all/[email protected]/ [1]
Signed-off-by: Muchun Song <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Anshuman Khandual <[email protected]>
---
arch/arm64/mm/flush.c | 13 +++----------
include/linux/page-flags.h | 14 ++------------
2 files changed, 5 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
index fc4f710e9820..5f9379b3c8c8 100644
--- a/arch/arm64/mm/flush.c
+++ b/arch/arm64/mm/flush.c
@@ -76,17 +76,10 @@ EXPORT_SYMBOL_GPL(__sync_icache_dcache);
void flush_dcache_page(struct page *page)
{
/*
- * Only the head page's flags of HugeTLB can be cleared since the tail
- * vmemmap pages associated with each HugeTLB page are mapped with
- * read-only when CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is enabled (more
- * details can refer to vmemmap_remap_pte()). Although
- * __sync_icache_dcache() only set PG_dcache_clean flag on the head
- * page struct, there is more than one page struct with PG_dcache_clean
- * associated with the HugeTLB page since the head vmemmap page frame
- * is reused (more details can refer to the comments above
- * page_fixed_fake_head()).
+ * HugeTLB pages are always fully mapped and only head page will be
+ * set PG_dcache_clean (see comments in __sync_icache_dcache()).
*/
- if (hugetlb_optimize_vmemmap_enabled() && PageHuge(page))
+ if (PageHuge(page))
page = compound_head(page);

if (test_bit(PG_dcache_clean, &page->flags))
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index de80f0c26b2f..b8b992cb201c 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -203,12 +203,6 @@ enum pageflags {
DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
hugetlb_optimize_vmemmap_key);

-static __always_inline bool hugetlb_optimize_vmemmap_enabled(void)
-{
- return static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
- &hugetlb_optimize_vmemmap_key);
-}
-
/*
* If the feature of optimizing vmemmap pages associated with each HugeTLB
* page is enabled, the head vmemmap page frame is reused and all of the tail
@@ -227,7 +221,8 @@ static __always_inline bool hugetlb_optimize_vmemmap_enabled(void)
*/
static __always_inline const struct page *page_fixed_fake_head(const struct page *page)
{
- if (!hugetlb_optimize_vmemmap_enabled())
+ if (!static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
+ &hugetlb_optimize_vmemmap_key))
return page;

/*
@@ -255,11 +250,6 @@ static inline const struct page *page_fixed_fake_head(const struct page *page)
{
return page;
}
-
-static inline bool hugetlb_optimize_vmemmap_enabled(void)
-{
- return false;
-}
#endif

static __always_inline int page_is_fake_head(struct page *page)
--
2.11.0

2022-06-13 08:13:02

by Oscar Salvador

[permalink] [raw]

Subject: Re: [PATCH 1/6] mm: hugetlb_vmemmap: delete hugetlb_optimize_vmemmap_enabled()

On Mon, Jun 13, 2022 at 02:35:07PM +0800, Muchun Song wrote:
> The name hugetlb_optimize_vmemmap_enabled() a bit confusing as it tests
> two conditions (enabled and pages in use). Instead of coming up to
> an appropriate name, we could just delete it. There is already a
> discussion about deleting it in thread [1].
>
> There is only one user of hugetlb_optimize_vmemmap_enabled() outside of
> hugetlb_vmemmap, that is flush_dcache_page() in arch/arm64/mm/flush.c.
> However, it does not need to call hugetlb_optimize_vmemmap_enabled()
> in flush_dcache_page() since HugeTLB pages are always fully mapped and
> only head page will be set PG_dcache_clean meaning only head page's flag
> may need to be cleared (see commit cf5a501d985b). So it is easy to
> remove hugetlb_optimize_vmemmap_enabled().
>
> Link: https://lore.kernel.org/all/[email protected]/ [1]
> Signed-off-by: Muchun Song <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Anshuman Khandual <[email protected]>

Reviewed-by: Oscar Salvador <[email protected]>

--
Oscar Salvador
SUSE Labs

2022-06-13 20:07:07

by Mike Kravetz

[permalink] [raw]

Subject: Re: [PATCH 1/6] mm: hugetlb_vmemmap: delete hugetlb_optimize_vmemmap_enabled()

On Mon, Jun 13, 2022 at 02:35:07PM +0800”, Muchun Song wrote:
> The name hugetlb_optimize_vmemmap_enabled() a bit confusing as it tests
> two conditions (enabled and pages in use). Instead of coming up to
> an appropriate name, we could just delete it. There is already a
> discussion about deleting it in thread [1].
>
> There is only one user of hugetlb_optimize_vmemmap_enabled() outside of
> hugetlb_vmemmap, that is flush_dcache_page() in arch/arm64/mm/flush.c.
> However, it does not need to call hugetlb_optimize_vmemmap_enabled()
> in flush_dcache_page() since HugeTLB pages are always fully mapped and
> only head page will be set PG_dcache_clean meaning only head page's flag
> may need to be cleared (see commit cf5a501d985b). So it is easy to
> remove hugetlb_optimize_vmemmap_enabled().
>
> Link: https://lore.kernel.org/all/[email protected]/ [1]
> Signed-off-by: Muchun Song <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Anshuman Khandual <[email protected]>
> ---
> arch/arm64/mm/flush.c | 13 +++----------
> include/linux/page-flags.h | 14 ++------------
> 2 files changed, 5 insertions(+), 22 deletions(-)

Thanks. I think this makes the code less confusing.

Reviewed-by: Mike Kravetz <[email protected]>
--
Mike Kravetz

2022-06-20 17:04:59

by Catalin Marinas

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