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mlock: mlocked pages are unevictable

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Make sure that mlocked pages also live on the unevictable LRU, so kswapd
will not scan them over and over again.

This is achieved through various strategies:

1) add yet another page flag--PG_mlocked--to indicate that
   the page is locked for efficient testing in vmscan and,
   optionally, fault path.  This allows early culling of
   unevictable pages, preventing them from getting to
   page_referenced()/try_to_unmap().  Also allows separate
   accounting of mlock'd pages, as Nick's original patch
   did.

   Note:  Nick's original mlock patch used a PG_mlocked
   flag.  I had removed this in favor of the PG_unevictable
   flag + an mlock_count [new page struct member].  I
   restored the PG_mlocked flag to eliminate the new
   count field.

2) add the mlock/unevictable infrastructure to mm/mlock.c,
   with internal APIs in mm/internal.h.  This is a rework
   of Nick's original patch to these files, taking into
   account that mlocked pages are now kept on unevictable
   LRU list.

3) update vmscan.c:page_evictable() to check PageMlocked()
   and, if vma passed in, the vm_flags.  Note that the vma
   will only be passed in for new pages in the fault path;
   and then only if the "cull unevictable pages in fault
   path" patch is included.

4) add try_to_unlock() to rmap.c to walk a page's rmap and
   ClearPageMlocked() if no other vmas have it mlocked.
   Reuses as much of try_to_unmap() as possible.  This
   effectively replaces the use of one of the lru list links
   as an mlock count.  If this mechanism let's pages in mlocked
   vmas leak through w/o PG_mlocked set [I don't know that it
   does], we should catch them later in try_to_unmap().  One
   hopes this will be rare, as it will be relatively expensive.

Original mm/internal.h, mm/rmap.c and mm/mlock.c changes:
Signed-off-by: Nick Piggin <[email protected]>

splitlru: introduce __get_user_pages():

  New munlock processing need to GUP_FLAGS_IGNORE_VMA_PERMISSIONS.
  because current get_user_pages() can't grab PROT_NONE pages theresore it
  cause PROT_NONE pages can't munlock.

[[email protected]: fix this for pagemap-pass-mm-into-pagewalkers.patch]
[[email protected]: untangle patch interdependencies]
[[email protected]: fix things after out-of-order merging]
[[email protected]: fix page-flags mess]
[[email protected]: fix munlock page table walk - now requires 'mm']
[[email protected]: build fix]
[[email protected]: fix truncate race and sevaral comments]
[[email protected]: splitlru: introduce __get_user_pages()]
Signed-off-by: KOSAKI Motohiro <[email protected]>
Signed-off-by: Rik van Riel <[email protected]>
Signed-off-by: Lee Schermerhorn <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Matt Mackall <[email protected]>
Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Nick Piggin 2008-10-18 20:26:44 -07:00 • committed by Linus Torvalds
commit b291f00039
13 changed files with 817 additions and 91 deletions
Download patch file Download diff file Expand all files Collapse all files

36
mm/vmscan.c
View file

@ -582,11 +582,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
sc->nr_scanned++;
if (unlikely(!page_evictable(page, NULL))) {
unlock_page(page);
putback_lru_page(page);
continue;
}
if (unlikely(!page_evictable(page, NULL)))
goto cull_mlocked;
if (!sc->may_swap && page_mapped(page))
goto keep_locked;
@ -624,9 +621,19 @@ static unsigned long shrink_page_list(struct list_head *page_list,
* Anonymous process memory has backing store?
* Try to allocate it some swap space here.
*/
if (PageAnon(page) && !PageSwapCache(page))
if (PageAnon(page) && !PageSwapCache(page)) {
switch (try_to_munlock(page)) {
case SWAP_FAIL: /* shouldn't happen */
case SWAP_AGAIN:
goto keep_locked;
case SWAP_MLOCK:
goto cull_mlocked;
case SWAP_SUCCESS:
; /* fall thru'; add to swap cache */
}
if (!add_to_swap(page, GFP_ATOMIC))
goto activate_locked;
}
#endif /* CONFIG_SWAP */
mapping = page_mapping(page);
@ -641,6 +648,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
goto activate_locked;
case SWAP_AGAIN:
goto keep_locked;
case SWAP_MLOCK:
goto cull_mlocked;
case SWAP_SUCCESS:
; /* try to free the page below */
}
@ -731,6 +740,11 @@ free_it:
}
continue;
cull_mlocked:
unlock_page(page);
putback_lru_page(page);
continue;
activate_locked:
/* Not a candidate for swapping, so reclaim swap space. */
if (PageSwapCache(page) && vm_swap_full())
@ -742,7 +756,7 @@ keep_locked:
unlock_page(page);
keep:
list_add(&page->lru, &ret_pages);
VM_BUG_ON(PageLRU(page));
VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
}
list_splice(&ret_pages, page_list);
if (pagevec_count(&freed_pvec))
@ -2329,12 +2343,13 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
* @vma: the VMA in which the page is or will be mapped, may be NULL
*
* Test whether page is evictable--i.e., should be placed on active/inactive
* lists vs unevictable list.
* lists vs unevictable list. The vma argument is !NULL when called from the
* fault path to determine how to instantate a new page.
*
* Reasons page might not be evictable:
* (1) page's mapping marked unevictable
* (2) page is part of an mlocked VMA
*
* TODO - later patches
*/
int page_evictable(struct page *page, struct vm_area_struct *vma)
{
@ -2342,7 +2357,8 @@ int page_evictable(struct page *page, struct vm_area_struct *vma)
if (mapping_unevictable(page_mapping(page)))
return 0;
/* TODO: test page [!]evictable conditions */
if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
return 0;
return 1;
}