[RFC][PATCH] proc: export more page flags in /proc/kpageflags(take 3)
From: Wu Fengguang
Date: Wed Apr 22 2009 - 22:27:22 EST
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@xxxxxxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Matt Mackall <mpm@xxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
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:
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