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Date: Sat, 25 Apr 2009 09:59:11 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Andi Kleen <andi@...stfloor.org>,
Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] proc: export more page flags in /proc/kpageflags
(take 3)
Hi all,
For your convenience, I attached the uptodate code for page-types and
page-areas. Enjoy hacking~
Thanks,
Fengguang
On Thu, Apr 23, 2009 at 10:26:25AM +0800, Wu Fengguang wrote:
> Andi and KOSAKI: can we hopefully reach harmony of opinions on this version?
>
> Export 9 page flags in /proc/kpageflags, and 8 more for kernel developers.
>
> 1) for kernel hackers (on CONFIG_DEBUG_KERNEL)
> - all available page flags are exported, and
> - exported as is
> 2) for admins and end users
> - only the more `well known' flags are exported:
> 11. KPF_MMAP (pseudo flag) memory mapped page
> 12. KPF_ANON (pseudo flag) memory mapped page (anonymous)
> 13. KPF_SWAPCACHE page is in swap cache
> 14. KPF_SWAPBACKED page is swap/RAM backed
> 15. KPF_COMPOUND_HEAD (*)
> 16. KPF_COMPOUND_TAIL (*)
> 17. KPF_UNEVICTABLE page is in the unevictable LRU list
> 18. KPF_POISON hardware detected corruption
> 19. KPF_NOPAGE (pseudo flag) no page frame at the address
>
> (*) For compound pages, exporting _both_ head/tail info enables
> users to tell where a compound page starts/ends, and its order.
>
> - limit flags to their typical usage scenario, as indicated by KOSAKI:
> - LRU pages: only export relevant flags
> - PG_lru
> - PG_unevictable
> - PG_active
> - PG_referenced
> - page_mapped()
> - PageAnon()
> - PG_swapcache
> - PG_swapbacked
> - PG_reclaim
> - no-IO pages: mask out irrelevant flags
> - PG_dirty
> - PG_uptodate
> - PG_writeback
> - SLAB pages: mask out overloaded flags:
> - PG_error
> - PG_active
> - PG_private
> - PG_reclaim: filter out the overloaded PG_readahead
>
> Note that compound page flags are exported faithfully to end user. This risks
> exposing internal implementation details of the SLUB allocator, however hiding
> it risks larger impacts:
> - admins may wonder where all the compound pages gone - the use of
> compound pages in SLUB might have some real world relevance, so that
> end users want to be aware of this behavior
> - admins may be confused on inconsistent number of head/tail segments
> This is because SLUB only marks PG_slab on the compound head page.
> If we mask out PG_head|PG_tail for PG_slab pages, we are actually
> only masking out PG_head flags. Therefore the PG_tail segments will
> outnumber PG_head ones, which puzzled me for some time..
>
> Here are the admin/linus views of all page flags on a newly booted nfs-root system:
>
> # ./page-types # for admin
> flags page-count MB symbolic-flags long-symbolic-flags
> 0x000000000000 491449 1919 ____________________________
> 0x000000008000 15 0 _______________H____________ compound_head
> 0x000000010000 4280 16 ________________T___________ compound_tail
> 0x000000000008 17 0 ___U________________________ uptodate
> 0x000000008010 1 0 ____D__________H____________ dirty,compound_head
> 0x000000010010 4 0 ____D___________T___________ dirty,compound_tail
> 0x000000000020 1 0 _____l______________________ lru
> 0x000000000028 2678 10 ___U_l______________________ uptodate,lru
> 0x00000000002c 5244 20 __RU_l______________________ referenced,uptodate,lru
> 0x000000004060 1 0 _____lA_______b_____________ lru,active,swapbacked
> 0x000000004064 13 0 __R__lA_______b_____________ referenced,lru,active,swapbacked
> 0x000000000068 236 0 ___U_lA_____________________ uptodate,lru,active
> 0x00000000006c 927 3 __RU_lA_____________________ referenced,uptodate,lru,active
> 0x000000008080 968 3 _______S_______H____________ slab,compound_head
> 0x000000000080 1539 6 _______S____________________ slab
> 0x000000000400 516 2 __________B_________________ buddy
> 0x000000000828 1142 4 ___U_l_____M________________ uptodate,lru,mmap
> 0x00000000082c 280 1 __RU_l_____M________________ referenced,uptodate,lru,mmap
> 0x000000004860 2 0 _____lA____M__b_____________ lru,active,mmap,swapbacked
> 0x000000000868 366 1 ___U_lA____M________________ uptodate,lru,active,mmap
> 0x00000000086c 623 2 __RU_lA____M________________ referenced,uptodate,lru,active,mmap
> 0x000000005868 3639 14 ___U_lA____Ma_b_____________ uptodate,lru,active,mmap,anonymous,swapbacked
> 0x00000000586c 27 0 __RU_lA____Ma_b_____________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
> total 513968 2007
>
> # ./page-types # for linus, when CONFIG_DEBUG_KERNEL is turned on
> flags page-count MB symbolic-flags long-symbolic-flags
> 0x000000000000 471731 1842 ____________________________
> 0x000100000000 19258 75 ____________________r_______ reserved
> 0x000000008000 15 0 _______________H____________ compound_head
> 0x000000010000 4270 16 ________________T___________ compound_tail
> 0x000000000008 3 0 ___U________________________ uptodate
> 0x000000008014 1 0 __R_D__________H____________ referenced,dirty,compound_head
> 0x000000010014 4 0 __R_D___________T___________ referenced,dirty,compound_tail
> 0x000000000020 1 0 _____l______________________ lru
> 0x000000000028 2626 10 ___U_l______________________ uptodate,lru
> 0x00000000002c 5244 20 __RU_l______________________ referenced,uptodate,lru
> 0x000000000068 238 0 ___U_lA_____________________ uptodate,lru,active
> 0x00000000006c 925 3 __RU_lA_____________________ referenced,uptodate,lru,active
> 0x000000004078 1 0 ___UDlA_______b_____________ uptodate,dirty,lru,active,swapbacked
> 0x00000000407c 13 0 __RUDlA_______b_____________ referenced,uptodate,dirty,lru,active,swapbacked
> 0x000000000228 49 0 ___U_l___I__________________ uptodate,lru,reclaim
> 0x000000000400 523 2 __________B_________________ buddy
> 0x000000000804 1 0 __R________M________________ referenced,mmap
> 0x00000000080c 1 0 __RU_______M________________ referenced,uptodate,mmap
> 0x000000000828 1142 4 ___U_l_____M________________ uptodate,lru,mmap
> 0x00000000082c 280 1 __RU_l_____M________________ referenced,uptodate,lru,mmap
> 0x000000000868 366 1 ___U_lA____M________________ uptodate,lru,active,mmap
> 0x00000000086c 622 2 __RU_lA____M________________ referenced,uptodate,lru,active,mmap
> 0x000000004878 2 0 ___UDlA____M__b_____________ uptodate,dirty,lru,active,mmap,swapbacked
> 0x000000008880 907 3 _______S___M___H____________ slab,mmap,compound_head
> 0x000000000880 1488 5 _______S___M________________ slab,mmap
> 0x0000000088c0 59 0 ______AS___M___H____________ active,slab,mmap,compound_head
> 0x0000000008c0 49 0 ______AS___M________________ active,slab,mmap
> 0x000000001000 465 1 ____________a_______________ anonymous
> 0x000000005008 8 0 ___U________a_b_____________ uptodate,anonymous,swapbacked
> 0x000000005808 4 0 ___U_______Ma_b_____________ uptodate,mmap,anonymous,swapbacked
> 0x00000000580c 1 0 __RU_______Ma_b_____________ referenced,uptodate,mmap,anonymous,swapbacked
> 0x000000005868 3645 14 ___U_lA____Ma_b_____________ uptodate,lru,active,mmap,anonymous,swapbacked
> 0x00000000586c 26 0 __RU_lA____Ma_b_____________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
> total 513968 2007
>
> Kudos to KOSAKI and Andi for the extensive recommendations!
>
> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: Matt Mackall <mpm@...enic.com>
> Cc: Alexey Dobriyan <adobriyan@...il.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
> Documentation/vm/pagemap.txt | 65 ++++++++++
> fs/proc/page.c | 197 +++++++++++++++++++++++++++------
> 2 files changed, 227 insertions(+), 35 deletions(-)
>
> --- mm.orig/fs/proc/page.c
> +++ mm/fs/proc/page.c
> @@ -6,6 +6,7 @@
> #include <linux/mmzone.h>
> #include <linux/proc_fs.h>
> #include <linux/seq_file.h>
> +#include <linux/backing-dev.h>
> #include <asm/uaccess.h>
> #include "internal.h"
>
> @@ -68,19 +69,167 @@ static const struct file_operations proc
>
> /* These macros are used to decouple internal flags from exported ones */
>
> -#define KPF_LOCKED 0
> -#define KPF_ERROR 1
> -#define KPF_REFERENCED 2
> -#define KPF_UPTODATE 3
> -#define KPF_DIRTY 4
> -#define KPF_LRU 5
> -#define KPF_ACTIVE 6
> -#define KPF_SLAB 7
> -#define KPF_WRITEBACK 8
> -#define KPF_RECLAIM 9
> -#define KPF_BUDDY 10
> +#define KPF_LOCKED 0
> +#define KPF_ERROR 1
> +#define KPF_REFERENCED 2
> +#define KPF_UPTODATE 3
> +#define KPF_DIRTY 4
> +#define KPF_LRU 5
> +#define KPF_ACTIVE 6
> +#define KPF_SLAB 7
> +#define KPF_WRITEBACK 8
> +#define KPF_RECLAIM 9
> +#define KPF_BUDDY 10
> +
> +/* new additions in 2.6.31 */
> +#define KPF_MMAP 11
> +#define KPF_ANON 12
> +#define KPF_SWAPCACHE 13
> +#define KPF_SWAPBACKED 14
> +#define KPF_COMPOUND_HEAD 15
> +#define KPF_COMPOUND_TAIL 16
> +#define KPF_UNEVICTABLE 17
> +#define KPF_POISON 18
> +#define KPF_NOPAGE 19
> +
> +/* kernel hacking assistances */
> +#define KPF_RESERVED 32
> +#define KPF_MLOCKED 33
> +#define KPF_MAPPEDTODISK 34
> +#define KPF_PRIVATE 35
> +#define KPF_PRIVATE2 36
> +#define KPF_OWNER_PRIVATE 37
> +#define KPF_ARCH 38
> +#define KPF_UNCACHED 39
> +
> +/*
> + * Kernel flags are exported faithfully to Linus and his fellow hackers.
> + * Otherwise some details are masked to avoid confusing the end user:
> + * - some kernel flags are completely invisible
> + * - some kernel flags are conditionally invisible on their odd usages
> + */
> +#ifdef CONFIG_DEBUG_KERNEL
> +static inline int genuine_linus(void) { return 1; }
> +#else
> +static inline int genuine_linus(void) { return 0; }
> +#endif
> +
> +#define kpf_copy_bit(uflags, kflags, visible, ubit, kbit) \
> + do { \
> + if (visible || genuine_linus()) \
> + uflags |= ((kflags >> kbit) & 1) << ubit; \
> + } while (0);
> +
> +/* a helper function _not_ intended for more general uses */
> +static inline int page_cap_writeback_dirty(struct page *page)
> +{
> + struct address_space *mapping = NULL;
> +
> + if (!PageSlab(page))
> + mapping = page_mapping(page);
> +
> + return !mapping || mapping_cap_writeback_dirty(mapping);
> +}
>
> -#define kpf_copy_bit(flags, dstpos, srcpos) (((flags >> srcpos) & 1) << dstpos)
> +static u64 get_uflags(struct page *page)
> +{
> + u64 k;
> + u64 u;
> + int io;
> + int lru;
> + int slab;
> +
> + /*
> + * pseudo flag: KPF_NOPAGE
> + * it differentiates a memory hole from a page with no flags
> + */
> + if (!page)
> + return 1 << KPF_NOPAGE;
> +
> + k = page->flags;
> + u = 0;
> +
> + io = page_cap_writeback_dirty(page);
> + lru = k & (1 << PG_lru);
> + slab = k & (1 << PG_slab);
> +
> + /*
> + * pseudo flags for the well known (anonymous) memory mapped pages
> + */
> + if (lru || genuine_linus()) {
> + if (page_mapped(page))
> + u |= 1 << KPF_MMAP;
> + if (PageAnon(page))
> + u |= 1 << KPF_ANON;
> + }
> +
> + /*
> + * compound pages: export both head/tail info
> + * they together define a compound page's start/end pos and order
> + */
> + if (PageHead(page))
> + u |= 1 << KPF_COMPOUND_HEAD;
> + if (PageTail(page))
> + u |= 1 << KPF_COMPOUND_TAIL;
> +
> + kpf_copy_bit(u, k, 1, KPF_LOCKED, PG_locked);
> +
> + kpf_copy_bit(u, k, 1, KPF_SLAB, PG_slab);
> + kpf_copy_bit(u, k, 1, KPF_BUDDY, PG_buddy);
> +
> + kpf_copy_bit(u, k, io, KPF_ERROR, PG_error);
> + kpf_copy_bit(u, k, io, KPF_DIRTY, PG_dirty);
> + kpf_copy_bit(u, k, io, KPF_UPTODATE, PG_uptodate);
> + kpf_copy_bit(u, k, io, KPF_WRITEBACK, PG_writeback);
> +
> + kpf_copy_bit(u, k, 1, KPF_LRU, PG_lru);
> + kpf_copy_bit(u, k, lru, KPF_REFERENCED, PG_referenced);
> + kpf_copy_bit(u, k, lru, KPF_ACTIVE, PG_active);
> + kpf_copy_bit(u, k, lru, KPF_RECLAIM, PG_reclaim);
> +
> + kpf_copy_bit(u, k, lru, KPF_SWAPCACHE, PG_swapcache);
> + kpf_copy_bit(u, k, lru, KPF_SWAPBACKED, PG_swapbacked);
> +
> +#ifdef CONFIG_MEMORY_FAILURE
> + kpf_copy_bit(u, k, 1, KPF_POISON, PG_poison);
> +#endif
> +
> +#ifdef CONFIG_UNEVICTABLE_LRU
> + kpf_copy_bit(u, k, lru, KPF_UNEVICTABLE, PG_unevictable);
> + kpf_copy_bit(u, k, 0, KPF_MLOCKED, PG_mlocked);
> +#endif
> +
> + kpf_copy_bit(u, k, 0, KPF_RESERVED, PG_reserved);
> + kpf_copy_bit(u, k, 0, KPF_MAPPEDTODISK, PG_mappedtodisk);
> + kpf_copy_bit(u, k, 0, KPF_PRIVATE, PG_private);
> + kpf_copy_bit(u, k, 0, KPF_PRIVATE2, PG_private_2);
> + kpf_copy_bit(u, k, 0, KPF_OWNER_PRIVATE, PG_owner_priv_1);
> + kpf_copy_bit(u, k, 0, KPF_ARCH, PG_arch_1);
> +
> +#ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
> + kpf_copy_bit(u, k, 0, KPF_UNCACHED, PG_uncached);
> +#endif
> +
> + if (!genuine_linus()) {
> + /*
> + * SLAB/SLOB/SLUB overload some page flags which may confuse end user
> + */
> + if (slab) {
> + u &= ~ ((1 << KPF_ACTIVE) |
> + (1 << KPF_ERROR) |
> + (1 << KPF_MMAP));
> + }
> + /*
> + * PG_reclaim could be overloaded as PG_readahead,
> + * and we only want to export the first one.
> + */
> + if ((u & ((1 << KPF_RECLAIM) | (1 << KPF_WRITEBACK))) ==
> + (1 << KPF_RECLAIM))
> + u &= ~ (1 << KPF_RECLAIM);
> + }
> +
> + return u;
> +};
>
> static ssize_t kpageflags_read(struct file *file, char __user *buf,
> size_t count, loff_t *ppos)
> @@ -90,7 +239,6 @@ static ssize_t kpageflags_read(struct fi
> unsigned long src = *ppos;
> unsigned long pfn;
> ssize_t ret = 0;
> - u64 kflags, uflags;
>
> pfn = src / KPMSIZE;
> count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);
> @@ -98,32 +246,17 @@ static ssize_t kpageflags_read(struct fi
> return -EINVAL;
>
> while (count > 0) {
> - ppage = NULL;
> if (pfn_valid(pfn))
> ppage = pfn_to_page(pfn);
> - pfn++;
> - if (!ppage)
> - kflags = 0;
> else
> - kflags = ppage->flags;
> -
> - uflags = kpf_copy_bit(kflags, KPF_LOCKED, PG_locked) |
> - kpf_copy_bit(kflags, KPF_ERROR, PG_error) |
> - kpf_copy_bit(kflags, KPF_REFERENCED, PG_referenced) |
> - kpf_copy_bit(kflags, KPF_UPTODATE, PG_uptodate) |
> - kpf_copy_bit(kflags, KPF_DIRTY, PG_dirty) |
> - kpf_copy_bit(kflags, KPF_LRU, PG_lru) |
> - kpf_copy_bit(kflags, KPF_ACTIVE, PG_active) |
> - kpf_copy_bit(kflags, KPF_SLAB, PG_slab) |
> - kpf_copy_bit(kflags, KPF_WRITEBACK, PG_writeback) |
> - kpf_copy_bit(kflags, KPF_RECLAIM, PG_reclaim) |
> - kpf_copy_bit(kflags, KPF_BUDDY, PG_buddy);
> + ppage = NULL;
>
> - if (put_user(uflags, out++)) {
> + if (put_user(get_uflags(ppage), out)) {
> ret = -EFAULT;
> break;
> }
> -
> + out++;
> + pfn++;
> count -= KPMSIZE;
> }
>
> --- mm.orig/Documentation/vm/pagemap.txt
> +++ mm/Documentation/vm/pagemap.txt
> @@ -12,9 +12,9 @@ There are three components to pagemap:
> value for each virtual page, containing the following data (from
> fs/proc/task_mmu.c, above pagemap_read):
>
> - * Bits 0-55 page frame number (PFN) if present
> + * Bits 0-54 page frame number (PFN) if present
> * Bits 0-4 swap type if swapped
> - * Bits 5-55 swap offset if swapped
> + * Bits 5-54 swap offset if swapped
> * Bits 55-60 page shift (page size = 1<<page shift)
> * Bit 61 reserved for future use
> * Bit 62 page swapped
> @@ -36,7 +36,7 @@ There are three components to pagemap:
> * /proc/kpageflags. This file contains a 64-bit set of flags for each
> page, indexed by PFN.
>
> - The flags are (from fs/proc/proc_misc, above kpageflags_read):
> + The flags are (from fs/proc/page.c, above kpageflags_read):
>
> 0. LOCKED
> 1. ERROR
> @@ -49,6 +49,65 @@ There are three components to pagemap:
> 8. WRITEBACK
> 9. RECLAIM
> 10. BUDDY
> + 11. MMAP
> + 12. ANON
> + 13. SWAPCACHE
> + 14. SWAPBACKED
> + 15. COMPOUND_HEAD
> + 16. COMPOUND_TAIL
> + 17. UNEVICTABLE
> + 18. POISON
> + 19. NOPAGE
> +
> +Short descriptions to the page flags:
> +
> + 0. LOCKED
> + page is being locked for exclusive access, eg. by undergoing read/write IO
> +
> + 7. SLAB
> + page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator
> +
> +10. BUDDY
> + a free memory block managed by the buddy system allocator
> + The buddy system organizes free memory in blocks of various orders.
> + An order N block has 2^N physically contiguous pages, with the BUDDY flag
> + set for and _only_ for the first page.
> +
> +15. COMPOUND_HEAD
> +16. COMPOUND_TAIL
> + A compound page with order N consists of 2^N physically contiguous pages.
> + A compound page with order 2 takes the form of "HTTT", where H donates its
> + head page and T donates its tail page(s). The major consumers of compound
> + pages are hugeTLB pages (Documentation/vm/hugetlbpage.txt), the SLUB etc.
> + memory allocators and various device drivers.
> +
> +18. POISON
> + hardware has detected memory corruption on this page
> +
> +19. NOPAGE
> + no page frame exists at the requested address
> +
> + [IO related page flags]
> + 1. ERROR IO error occurred
> + 3. UPTODATE page has up-to-date data
> + ie. for file backed page: (in-memory data revision >= on-disk one)
> + 4. DIRTY page has been written to, hence contains new data
> + ie. for file backed page: (in-memory data revision > on-disk one)
> + 8. WRITEBACK page is being synced to disk
> +
> + [LRU related page flags]
> + 5. LRU page is in one of the LRU lists
> + 6. ACTIVE page is in the active LRU list
> +17. UNEVICTABLE page is in the unevictable (non-)LRU list
> + It is somehow pinned and not a candidate for LRU page reclaims,
> + eg. ramfs pages, shmctl(SHM_LOCK) and mlock() memory segments
> + 2. REFERENCED page has been referenced since last LRU list enqueue/requeue
> + 9. RECLAIM page will be reclaimed soon after its pageout IO completed
> +11. MMAP a memory mapped page
> +12. ANON a memory mapped page who is not a file page
> +13. SWAPCACHE page is mapped to swap space, ie. has an associated swap entry
> +14. SWAPBACKED page is backed by swap/RAM
> +
>
> Using pagemap to do something useful:
>
View attachment "pagemap.h" of type "text/x-chdr" (2400 bytes)
View attachment "page-types.c" of type "text/x-csrc" (2656 bytes)
View attachment "page-areas.c" of type "text/x-csrc" (1495 bytes)
View attachment "Makefile" of type "text/plain" (170 bytes)
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