Permalink
Browse files

proc: report file/anon bit in /proc/pid/pagemap

This is an implementation of Andrew's proposal to extend the pagemap file
bits to report what is missing about tasks' working set.

The problem with the working set detection is multilateral.  In the criu
(checkpoint/restore) project we dump the tasks' memory into image files
and to do it properly we need to detect which pages inside mappings are
really in use.  The mincore syscall I though could help with this did not.
 First, it doesn't report swapped pages, thus we cannot find out which
parts of anonymous mappings to dump.  Next, it does report pages from page
cache as present even if they are not mapped, and it doesn't make that has
not been cow-ed.

Note, that issue with swap pages is critical -- we must dump swap pages to
image file.  But the issues with file pages are optimization -- we can
take all file pages to image, this would be correct, but if we know that a
page is not mapped or not cow-ed, we can remove them from dump file.  The
dump would still be self-consistent, though significantly smaller in size
(up to 10 times smaller on real apps).

Andrew noticed, that the proc pagemap file solved 2 of 3 above issues --
it reports whether a page is present or swapped and it doesn't report not
mapped page cache pages.  But, it doesn't distinguish cow-ed file pages
from not cow-ed.

I would like to make the last unused bit in this file to report whether the
page mapped into respective pte is PageAnon or not.

[comment stolen from Pavel Emelyanov's v1 patch]

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  • Loading branch information...
1 parent 715be1f commit 052fb0d635df5d49dfc85687d94e1a87bf09378d @koct9i koct9i committed with May 31, 2012
Showing with 31 additions and 19 deletions.
  1. +1 −1 Documentation/vm/pagemap.txt
  2. +30 −18 fs/proc/task_mmu.c
@@ -16,7 +16,7 @@ There are three components to pagemap:
* Bits 0-4 swap type 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 61 page is file-page or shared-anon
* Bit 62 page swapped
* Bit 63 page present
View
@@ -700,6 +700,7 @@ struct pagemapread {
#define PM_PRESENT PM_STATUS(4LL)
#define PM_SWAP PM_STATUS(2LL)
+#define PM_FILE PM_STATUS(1LL)
#define PM_NOT_PRESENT PM_PSHIFT(PAGE_SHIFT)
#define PM_END_OF_BUFFER 1
@@ -733,22 +734,33 @@ static int pagemap_pte_hole(unsigned long start, unsigned long end,
return err;
}
-static u64 swap_pte_to_pagemap_entry(pte_t pte)
+static void pte_to_pagemap_entry(pagemap_entry_t *pme,
+ struct vm_area_struct *vma, unsigned long addr, pte_t pte)
{
- swp_entry_t e = pte_to_swp_entry(pte);
- return swp_type(e) | (swp_offset(e) << MAX_SWAPFILES_SHIFT);
-}
-
-static void pte_to_pagemap_entry(pagemap_entry_t *pme, pte_t pte)
-{
- if (is_swap_pte(pte))
- *pme = make_pme(PM_PFRAME(swap_pte_to_pagemap_entry(pte))
- | PM_PSHIFT(PAGE_SHIFT) | PM_SWAP);
- else if (pte_present(pte))
- *pme = make_pme(PM_PFRAME(pte_pfn(pte))
- | PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT);
- else
+ u64 frame, flags;
+ struct page *page = NULL;
+
+ if (pte_present(pte)) {
+ frame = pte_pfn(pte);
+ flags = PM_PRESENT;
+ page = vm_normal_page(vma, addr, pte);
+ } else if (is_swap_pte(pte)) {
+ swp_entry_t entry = pte_to_swp_entry(pte);
+
+ frame = swp_type(entry) |
+ (swp_offset(entry) << MAX_SWAPFILES_SHIFT);
+ flags = PM_SWAP;
+ if (is_migration_entry(entry))
+ page = migration_entry_to_page(entry);
+ } else {
*pme = make_pme(PM_NOT_PRESENT);
+ return;
+ }
+
+ if (page && !PageAnon(page))
+ flags |= PM_FILE;
+
+ *pme = make_pme(PM_PFRAME(frame) | PM_PSHIFT(PAGE_SHIFT) | flags);
}
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
@@ -815,7 +827,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
if (vma && (vma->vm_start <= addr) &&
!is_vm_hugetlb_page(vma)) {
pte = pte_offset_map(pmd, addr);
- pte_to_pagemap_entry(&pme, *pte);
+ pte_to_pagemap_entry(&pme, vma, addr, *pte);
/* unmap before userspace copy */
pte_unmap(pte);
}
@@ -869,11 +881,11 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
* For each page in the address space, this file contains one 64-bit entry
* consisting of the following:
*
- * 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 61 page is file-page or shared-anon
* Bit 62 page swapped
* Bit 63 page present
*

0 comments on commit 052fb0d

Please sign in to comment.