From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> The flag field of slab tail pages is used for internal purpose and there's no point in exposing such info to userspace. Here's the output of `page-types -r -b slab` command now: flags page-count MB symbolic-flags long-symbolic-flags 0x0000000000000080 5304 20 _______S_____________________________________ slab 0x0000000000008080 1488 5 _______S_______H_____________________________ slab,compound_head 0x0000000000010081 365 1 L______S________T____________________________ locked,slab,compound_tail 0x0000000000010080 4142 16 _______S________T____________________________ slab,compound_tail 0x0000000000010180 649 2 _______SW_______T____________________________ slab,writeback,compound_tail 0x0000000000010181 474 1 L______SW_______T____________________________ locked,slab,writeback,compound_tail 0x0000000000201080 192 0 _______S____a________x_______________________ slab,anonymous,ksm 0x0000000000001080 427 1 _______S____a________________________________ slab,anonymous 0x0000000000409080 237 0 _______S____a__H______t______________________ slab,anonymous,compound_head,thp 0x0000000000411081 78 0 L______S____a___T_____t______________________ locked,slab,anonymous,compound_tail,thp 0x0000000000609080 77 0 _______S____a__H_____xt______________________ slab,anonymous,compound_head,ksm,thp 0x0000000000611081 32 0 L______S____a___T____xt______________________ locked,slab,anonymous,compound_tail,ksm,thp 0x0000000000411080 698 2 _______S____a___T_____t______________________ slab,anonymous,compound_tail,thp 0x0000000000611080 142 0 _______S____a___T____xt______________________ slab,anonymous,compound_tail,ksm,thp 0x0000000000611180 32 0 _______SW___a___T____xt______________________ slab,writeback,anonymous,compound_tail,ksm,thp 0x0000000000411181 95 0 L______SW___a___T_____t______________________ locked,slab,writeback,anonymous,compound_tail,thp 0x0000000000411180 64 0 _______SW___a___T_____t______________________ slab,writeback,anonymous,compound_tail,thp 0x0000000000611181 13 0 L______SW___a___T____xt______________________ locked,slab,writeback,anonymous,compound_tail,ksm,thp In this output, "locked" and "writeback" flags are completely pointless because these are encoded in folio->_flags_1 via folio_set_order() and those pages are actually not locked nor written back. As for "anonymous" and "ksm" flags, these are encoded in folio->mapping and the actual value is like 0xdead000000000003. I'm not sure how this value is set, but according to the comment in include/linux/page-flags.h: > * For slab pages, since slab reuses the bits in struct page to store its > * internal states, the page->mapping does not exist as such, nor do these > * flags below. So in order to avoid testing non-existent bits, please > * make sure that PageSlab(page) actually evaluates to false before calling > * the following functions (e.g., PageAnon). See mm/slab.h. , so we don't have to check PageAnon and PageKsm for slab pages. So return immediately when finding slab tail pages. Note that KPF_HWPOISON is special and it can be helpful to make it visible in /prock/kpageflag even on compound tail pages. After this patch, `page-types -r -b slab` command shows the following simpler output (without any invalid flags). 0x0000000000000080 5659 22 _______S_____________________________________ slab 0x0000000000008080 1644 6 _______S_______H_____________________________ slab,compound_head 0x0000000000010080 6196 24 _______S________T____________________________ slab,compound_tail Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> --- fs/proc/page.c | 44 ++++++++++++++++++++++---------------------- 1 file changed, 22 insertions(+), 22 deletions(-) diff --git a/fs/proc/page.c b/fs/proc/page.c index 9b6ded8a2c90..899b96a26fbd 100644 --- a/fs/proc/page.c +++ b/fs/proc/page.c @@ -122,18 +122,18 @@ u64 stable_page_flags(struct page *page) k = page->flags; u = 0; - /* - * pseudo flags for the well known (anonymous) memory mapped pages - * - * Note that page->_mapcount is overloaded in SLAB, so the - * simple test in page_mapped() is not enough. - */ - if (!PageSlab(page) && page_mapped(page)) - u |= 1 << KPF_MMAP; - if (PageAnon(page)) - u |= 1 << KPF_ANON; - if (PageKsm(page)) - u |= 1 << KPF_KSM; +#ifdef CONFIG_MEMORY_FAILURE + u |= kpf_copy_bit(k, KPF_HWPOISON, PG_hwpoison); +#endif + + if (PageSlab(page)) { + u |= 1 << KPF_SLAB; + if (PageHead(page)) + u |= 1 << KPF_COMPOUND_HEAD; + if (PageTail(page)) + u |= 1 << KPF_COMPOUND_TAIL; + return u; + } if (PageHuge(page)) { u |= 1 << KPF_HUGE; @@ -173,9 +173,18 @@ u64 stable_page_flags(struct page *page) } else if (is_zero_pfn(page_to_pfn(page))) u |= 1 << KPF_ZERO_PAGE; + /* + * pseudo flags for the well known (anonymous) memory mapped pages + */ + if (page_mapped(page)) + u |= 1 << KPF_MMAP; + if (PageAnon(page)) + u |= 1 << KPF_ANON; + if (PageKsm(page)) + u |= 1 << KPF_KSM; /* - * Caveats on high order pages: PG_buddy and PG_slab will only be set + * Caveats on high order pages: PG_buddy will only be set * on the head page. */ if (PageBuddy(page)) @@ -192,11 +201,6 @@ u64 stable_page_flags(struct page *page) u |= 1 << KPF_IDLE; u |= kpf_copy_bit(k, KPF_LOCKED, PG_locked); - - u |= kpf_copy_bit(k, KPF_SLAB, PG_slab); - if (PageTail(page) && PageSlab(page)) - u |= 1 << KPF_SLAB; - u |= kpf_copy_bit(k, KPF_ERROR, PG_error); u |= kpf_copy_bit(k, KPF_DIRTY, PG_dirty); u |= kpf_copy_bit(k, KPF_UPTODATE, PG_uptodate); @@ -214,10 +218,6 @@ u64 stable_page_flags(struct page *page) u |= kpf_copy_bit(k, KPF_UNEVICTABLE, PG_unevictable); u |= kpf_copy_bit(k, KPF_MLOCKED, PG_mlocked); -#ifdef CONFIG_MEMORY_FAILURE - u |= kpf_copy_bit(k, KPF_HWPOISON, PG_hwpoison); -#endif - #ifdef CONFIG_ARCH_USES_PG_UNCACHED u |= kpf_copy_bit(k, KPF_UNCACHED, PG_uncached); #endif -- 2.25.1