On 2024/3/21 22:24, Matthew Wilcox (Oracle) wrote:
> Reclaim the Slab page flag by using a spare bit in PageType. We are
> perennially short of page flags for various purposes, and now that
> the original SLAB allocator has been retired, SLUB does not use the
> mapcount/page_type field. This lets us remove a number of special cases
> for ignoring mapcount on Slab pages.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> include/linux/page-flags.h | 21 +++++++++++++++++----
> include/trace/events/mmflags.h | 2 +-
> mm/memory-failure.c | 9 ---------
> mm/slab.h | 2 +-
> 4 files changed, 19 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 94eb8a11a321..73e0b17c7728 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -109,7 +109,6 @@ enum pageflags {
> PG_active,
> PG_workingset,
> PG_error,
> - PG_slab,
> PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
> PG_arch_1,
> PG_reserved,
> @@ -524,7 +523,6 @@ PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
> TESTCLEARFLAG(Active, active, PF_HEAD)
> PAGEFLAG(Workingset, workingset, PF_HEAD)
> TESTCLEARFLAG(Workingset, workingset, PF_HEAD)
> -__PAGEFLAG(Slab, slab, PF_NO_TAIL)
> PAGEFLAG(Checked, checked, PF_NO_COMPOUND) /* Used by some filesystems */
>
> /* Xen */
> @@ -931,7 +929,7 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
> #endif
>
> /*
> - * For pages that are never mapped to userspace (and aren't PageSlab),
> + * For pages that are never mapped to userspace,
> * page_type may be used. Because it is initialised to -1, we invert the
> * sense of the bit, so __SetPageFoo *clears* the bit used for PageFoo, and
> * __ClearPageFoo *sets* the bit used for PageFoo. We reserve a few high and
> @@ -947,6 +945,7 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned)
> #define PG_table 0x00000200
> #define PG_guard 0x00000400
> #define PG_hugetlb 0x00000800
> +#define PG_slab 0x00001000
>
> #define PageType(page, flag) \
> ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
> @@ -1041,6 +1040,20 @@ PAGE_TYPE_OPS(Table, table, pgtable)
> */
> PAGE_TYPE_OPS(Guard, guard, guard)
>
> +FOLIO_TYPE_OPS(slab, slab)
> +
> +/**
> + * PageSlab - Determine if the page belongs to the slab allocator
> + * @page: The page to test.
> + *
> + * Context: Any context.
> + * Return: True for slab pages, false for any other kind of page.
> + */
> +static inline bool PageSlab(const struct page *page)
> +{
> + return folio_test_slab(page_folio(page));
> +}
> +
> #ifdef CONFIG_HUGETLB_PAGE
> FOLIO_TYPE_OPS(hugetlb, hugetlb)
> #else
> @@ -1121,7 +1134,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
> (1UL << PG_lru | 1UL << PG_locked | \
> 1UL << PG_private | 1UL << PG_private_2 | \
> 1UL << PG_writeback | 1UL << PG_reserved | \
> - 1UL << PG_slab | 1UL << PG_active | \
> + 1UL << PG_active | \
> 1UL << PG_unevictable | __PG_MLOCKED | LRU_GEN_MASK)
>
> /*
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index d55e53ac91bd..e46d6e82765e 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -107,7 +107,6 @@
> DEF_PAGEFLAG_NAME(lru), \
> DEF_PAGEFLAG_NAME(active), \
> DEF_PAGEFLAG_NAME(workingset), \
> - DEF_PAGEFLAG_NAME(slab), \
> DEF_PAGEFLAG_NAME(owner_priv_1), \
> DEF_PAGEFLAG_NAME(arch_1), \
> DEF_PAGEFLAG_NAME(reserved), \
> @@ -135,6 +134,7 @@ IF_HAVE_PG_ARCH_X(arch_3)
> #define DEF_PAGETYPE_NAME(_name) { PG_##_name, __stringify(_name) }
>
> #define __def_pagetype_names \
> + DEF_PAGETYPE_NAME(slab), \
> DEF_PAGETYPE_NAME(hugetlb), \
> DEF_PAGETYPE_NAME(offline), \
> DEF_PAGETYPE_NAME(guard), \
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 9349948f1abf..1cb41ba7870c 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1239,7 +1239,6 @@ static int me_huge_page(struct page_state *ps, struct page *p)
> #define mlock (1UL << PG_mlocked)
> #define lru (1UL << PG_lru)
> #define head (1UL << PG_head)
> -#define slab (1UL << PG_slab)
> #define reserved (1UL << PG_reserved)
>
> static struct page_state error_states[] = {
> @@ -1249,13 +1248,6 @@ static struct page_state error_states[] = {
> * PG_buddy pages only make a small fraction of all free pages.
> */
>
> - /*
> - * Could in theory check if slab page is free or if we can drop
> - * currently unused objects without touching them. But just
> - * treat it as standard kernel for now.
> - */
> - { slab, slab, MF_MSG_SLAB, me_kernel },
Will it be better to leave the above slab case here to catch possible unhandled obscure races with
slab? Though it looks like slab page shouldn't reach here.
Thanks.
