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Subject[PATCH 5/5] proc: export more page flags in /proc/kpageflags
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_HWPOISON 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: mask out the overloaded PG_readahead
- compound flags: only export huge/gigantic pages

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 491174 1918 ____________________________
0x000000000020 1 0 _____l______________________ lru
0x000000000028 2543 9 ___U_l______________________ uptodate,lru
0x00000000002c 5288 20 __RU_l______________________ referenced,uptodate,lru
0x000000004060 1 0 _____lA_______b_____________ lru,active,swapbacked
0x000000004064 19 0 __R__lA_______b_____________ referenced,lru,active,swapbacked
0x000000000068 225 0 ___U_lA_____________________ uptodate,lru,active
0x00000000006c 969 3 __RU_lA_____________________ referenced,uptodate,lru,active
0x000000000080 6832 26 _______S____________________ slab
0x000000000400 576 2 __________B_________________ buddy
0x000000000828 1159 4 ___U_l_____M________________ uptodate,lru,mmap
0x00000000082c 310 1 __RU_l_____M________________ referenced,uptodate,lru,mmap
0x000000004860 2 0 _____lA____M__b_____________ lru,active,mmap,swapbacked
0x000000000868 375 1 ___U_lA____M________________ uptodate,lru,active,mmap
0x00000000086c 635 2 __RU_lA____M________________ referenced,uptodate,lru,active,mmap
0x000000005860 3831 14 _____lA____Ma_b_____________ lru,active,mmap,anonymous,swapbacked
0x000000005864 28 0 __R__lA____Ma_b_____________ referenced,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 471058 1840 ____________________________
0x000100000000 19288 75 ____________________r_______ reserved
0x000000010000 1064 4 ________________T___________ compound_tail
0x000000008000 1 0 _______________H____________ compound_head
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 2522 9 ___U_l______________________ uptodate,lru
0x00000000002c 5207 20 __RU_l______________________ referenced,uptodate,lru
0x000000000068 203 0 ___U_lA_____________________ uptodate,lru,active
0x00000000006c 869 3 __RU_lA_____________________ referenced,uptodate,lru,active
0x000000004078 1 0 ___UDlA_______b_____________ uptodate,dirty,lru,active,swapbacked
0x00000000407c 19 0 __RUDlA_______b_____________ referenced,uptodate,dirty,lru,active,swapbacked
0x000000000080 5989 23 _______S____________________ slab
0x000000008080 778 3 _______S_______H____________ slab,compound_head
0x000000000228 44 0 ___U_l___I__________________ uptodate,lru,reclaim
0x00000000022c 39 0 __RU_l___I__________________ referenced,uptodate,lru,reclaim
0x000000000268 12 0 ___U_lA__I__________________ uptodate,lru,active,reclaim
0x00000000026c 44 0 __RU_lA__I__________________ referenced,uptodate,lru,active,reclaim
0x000000000400 550 2 __________B_________________ buddy
0x000000000804 1 0 __R________M________________ referenced,mmap
0x000000000828 1068 4 ___U_l_____M________________ uptodate,lru,mmap
0x00000000082c 326 1 __RU_l_____M________________ referenced,uptodate,lru,mmap
0x000000000868 335 1 ___U_lA____M________________ uptodate,lru,active,mmap
0x00000000086c 599 2 __RU_lA____M________________ referenced,uptodate,lru,active,mmap
0x000000004878 2 0 ___UDlA____M__b_____________ uptodate,dirty,lru,active,mmap,swapbacked
0x000000000a28 44 0 ___U_l___I_M________________ uptodate,lru,reclaim,mmap
0x000000000a2c 12 0 __RU_l___I_M________________ referenced,uptodate,lru,reclaim,mmap
0x000000000a68 8 0 ___U_lA__I_M________________ uptodate,lru,active,reclaim,mmap
0x000000000a6c 31 0 __RU_lA__I_M________________ referenced,uptodate,lru,active,reclaim,mmap
0x000000001000 442 1 ____________a_______________ anonymous
0x000000005808 7 0 ___U_______Ma_b_____________ uptodate,mmap,anonymous,swapbacked
0x000000005868 3371 13 ___U_lA____Ma_b_____________ uptodate,lru,active,mmap,anonymous,swapbacked
0x00000000586c 28 0 __RU_lA____Ma_b_____________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
total 513968 2007
Thanks to KOSAKI and Andi for their valuable recommendations!

Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/proc/page.c | 197 +++++++++++++++++++++++++++++++++++++++--------
1 file changed, 167 insertions(+), 30 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"

@@ -70,19 +71,172 @@ 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_HWPOISON 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;
+
+ if (!PageSlab(page))
+ mapping = page_mapping(page);
+ else
+ mapping = NULL;
+
+ return mapping && mapping_cap_writeback_dirty(mapping);
+}
+
+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 (!slab && page_mapped(page))
+ u |= 1 << KPF_MMAP;
+ if (PageAnon(page))
+ u |= 1 << KPF_ANON;
+ }

-#define kpf_copy_bit(flags, dstpos, srcpos) (((flags >> srcpos) & 1) << dstpos)
+ /*
+ * compound pages: export both head/tail info
+ * they together define a compound page's start/end pos and order
+ */
+ if (PageHuge(page) || genuine_linus()) {
+ 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);
+
+ /*
+ * Caveats on high order pages:
+ * PG_buddy will only be set on the head page; SLUB/SLQB do the same
+ * for PG_slab; SLOB won't set PG_slab at all on compound pages.
+ */
+ 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_HWPOISON, PG_hwpoison);
+#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()) {
+ /*
+ * SLUB overloads some page flags which may confuse end user.
+ */
+ if (slab)
+ u &= ~((1 << KPF_ACTIVE) | (1 << KPF_ERROR));
+ /*
+ * PG_reclaim could be overloaded as PG_readahead,
+ * and we only want to export the first one.
+ */
+ if (!(u & (1 << KPF_WRITEBACK)))
+ u &= ~(1 << KPF_RECLAIM);
+ }
+
+ return u;
+};

static ssize_t kpageflags_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
@@ -92,7 +246,6 @@ 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);
@@ -104,24 +257,8 @@ static ssize_t kpageflags_read(struct fi
ppage = pfn_to_page(pfn);
else
ppage = NULL;
- 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);

- if (put_user(uflags, out)) {
+ if (put_user(get_uflags(ppage), out)) {
ret = -EFAULT;
break;
}
--



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