SHM_UNLOCK: fix Unevictable pages stranded after swap
Commit cc39c6a9bb ("mm: account skipped entries to avoid looping in
find_get_pages") correctly fixed an infinite loop; but left a problem
that find_get_pages() on shmem would return 0 (appearing to callers to
mean end of tree) when it meets a run of nr_pages swap entries.
The only uses of find_get_pages() on shmem are via pagevec_lookup(),
called from invalidate_mapping_pages(), and from shmctl SHM_UNLOCK's
scan_mapping_unevictable_pages(). The first is already commented, and
not worth worrying about; but the second can leave pages on the
Unevictable list after an unusual sequence of swapping and locking.
Fix that by using shmem_find_get_pages_and_swap() (then ignoring the
swap) instead of pagevec_lookup().
But I don't want to contaminate vmscan.c with shmem internals, nor
shmem.c with LRU locking. So move scan_mapping_unevictable_pages() into
shmem.c, renaming it shmem_unlock_mapping(); and rename
check_move_unevictable_page() to check_move_unevictable_pages(), looping
down an array of pages, oftentimes under the same lock.
Leave out the "rotate unevictable list" block: that's a leftover from
when this was used for /proc/sys/vm/scan_unevictable_pages, whose flawed
handling involved looking at pages at tail of LRU.
Was there significance to the sequence first ClearPageUnevictable, then
test page_evictable, then SetPageUnevictable here? I think not, we're
under LRU lock, and have no barriers between those.
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: <stable@vger.kernel.org> [back to 3.1 but will need respins]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins
Linus Torvalds
Родитель
85046579bd
Коммит
245132643e
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@ -48,6 +48,7 @@ extern struct file *shmem_file_setup(const char *name,
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loff_t size, unsigned long flags);
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extern int shmem_zero_setup(struct vm_area_struct *);
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extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
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extern void shmem_unlock_mapping(struct address_space *mapping);
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extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
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pgoff_t index, gfp_t gfp_mask);
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extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);
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@ -273,7 +273,7 @@ static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
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#endif
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extern int page_evictable(struct page *page, struct vm_area_struct *vma);
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extern void scan_mapping_unevictable_pages(struct address_space *);
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extern void check_move_unevictable_pages(struct page **, int nr_pages);
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extern unsigned long scan_unevictable_pages;
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extern int scan_unevictable_handler(struct ctl_table *, int,
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@ -916,7 +916,7 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
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shp->mlock_user = NULL;
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get_file(shm_file);
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shm_unlock(shp);
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scan_mapping_unevictable_pages(shm_file->f_mapping);
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shmem_unlock_mapping(shm_file->f_mapping);
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fput(shm_file);
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goto out;
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}
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46
mm/shmem.c
46
mm/shmem.c
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@ -379,7 +379,7 @@ static int shmem_free_swap(struct address_space *mapping,
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/*
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* Pagevec may contain swap entries, so shuffle up pages before releasing.
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*/
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static void shmem_pagevec_release(struct pagevec *pvec)
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static void shmem_deswap_pagevec(struct pagevec *pvec)
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{
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int i, j;
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@ -389,7 +389,36 @@ static void shmem_pagevec_release(struct pagevec *pvec)
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pvec->pages[j++] = page;
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}
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pvec->nr = j;
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pagevec_release(pvec);
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}
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/*
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* SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
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*/
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void shmem_unlock_mapping(struct address_space *mapping)
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{
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struct pagevec pvec;
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pgoff_t indices[PAGEVEC_SIZE];
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pgoff_t index = 0;
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pagevec_init(&pvec, 0);
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/*
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* Minor point, but we might as well stop if someone else SHM_LOCKs it.
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*/
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while (!mapping_unevictable(mapping)) {
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/*
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* Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
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* has finished, if it hits a row of PAGEVEC_SIZE swap entries.
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*/
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pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
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PAGEVEC_SIZE, pvec.pages, indices);
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if (!pvec.nr)
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break;
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index = indices[pvec.nr - 1] + 1;
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shmem_deswap_pagevec(&pvec);
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check_move_unevictable_pages(pvec.pages, pvec.nr);
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pagevec_release(&pvec);
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cond_resched();
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}
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}
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/*
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@ -440,7 +469,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
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}
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unlock_page(page);
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}
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shmem_pagevec_release(&pvec);
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shmem_deswap_pagevec(&pvec);
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pagevec_release(&pvec);
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mem_cgroup_uncharge_end();
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cond_resched();
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index++;
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@ -470,7 +500,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
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continue;
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}
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if (index == start && indices[0] > end) {
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shmem_pagevec_release(&pvec);
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shmem_deswap_pagevec(&pvec);
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pagevec_release(&pvec);
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break;
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}
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mem_cgroup_uncharge_start();
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@ -494,7 +525,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
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}
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unlock_page(page);
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}
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shmem_pagevec_release(&pvec);
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shmem_deswap_pagevec(&pvec);
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pagevec_release(&pvec);
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mem_cgroup_uncharge_end();
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index++;
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}
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@ -2438,6 +2470,10 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
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return 0;
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}
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void shmem_unlock_mapping(struct address_space *mapping)
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{
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}
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void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
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{
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truncate_inode_pages_range(inode->i_mapping, lstart, lend);
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132
mm/vmscan.c
132
mm/vmscan.c
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@ -26,7 +26,6 @@
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#include <linux/buffer_head.h> /* for try_to_release_page(),
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buffer_heads_over_limit */
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#include <linux/mm_inline.h>
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#include <linux/pagevec.h>
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#include <linux/backing-dev.h>
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#include <linux/rmap.h>
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#include <linux/topology.h>
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@ -661,7 +660,7 @@ redo:
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* When racing with an mlock or AS_UNEVICTABLE clearing
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* (page is unlocked) make sure that if the other thread
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* does not observe our setting of PG_lru and fails
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* isolation/check_move_unevictable_page,
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* isolation/check_move_unevictable_pages,
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* we see PG_mlocked/AS_UNEVICTABLE cleared below and move
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* the page back to the evictable list.
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*
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@ -3501,106 +3500,57 @@ int page_evictable(struct page *page, struct vm_area_struct *vma)
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#ifdef CONFIG_SHMEM
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/**
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* check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
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* @page: page to check evictability and move to appropriate lru list
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* @zone: zone page is in
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* check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
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* @pages: array of pages to check
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* @nr_pages: number of pages to check
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*
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* Checks a page for evictability and moves the page to the appropriate
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* zone lru list.
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*
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* Restrictions: zone->lru_lock must be held, page must be on LRU and must
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* have PageUnevictable set.
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* Checks pages for evictability and moves them to the appropriate lru list.
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*
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* This function is only used for SysV IPC SHM_UNLOCK.
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*/
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static void check_move_unevictable_page(struct page *page, struct zone *zone)
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void check_move_unevictable_pages(struct page **pages, int nr_pages)
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{
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struct lruvec *lruvec;
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struct zone *zone = NULL;
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int pgscanned = 0;
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int pgrescued = 0;
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int i;
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VM_BUG_ON(PageActive(page));
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retry:
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ClearPageUnevictable(page);
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if (page_evictable(page, NULL)) {
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enum lru_list l = page_lru_base_type(page);
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for (i = 0; i < nr_pages; i++) {
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struct page *page = pages[i];
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struct zone *pagezone;
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__dec_zone_state(zone, NR_UNEVICTABLE);
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lruvec = mem_cgroup_lru_move_lists(zone, page,
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LRU_UNEVICTABLE, l);
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list_move(&page->lru, &lruvec->lists[l]);
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__inc_zone_state(zone, NR_INACTIVE_ANON + l);
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__count_vm_event(UNEVICTABLE_PGRESCUED);
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} else {
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/*
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* rotate unevictable list
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*/
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SetPageUnevictable(page);
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lruvec = mem_cgroup_lru_move_lists(zone, page, LRU_UNEVICTABLE,
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LRU_UNEVICTABLE);
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list_move(&page->lru, &lruvec->lists[LRU_UNEVICTABLE]);
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if (page_evictable(page, NULL))
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goto retry;
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}
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}
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/**
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* scan_mapping_unevictable_pages - scan an address space for evictable pages
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* @mapping: struct address_space to scan for evictable pages
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*
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* Scan all pages in mapping. Check unevictable pages for
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* evictability and move them to the appropriate zone lru list.
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*
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* This function is only used for SysV IPC SHM_UNLOCK.
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*/
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void scan_mapping_unevictable_pages(struct address_space *mapping)
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{
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pgoff_t next = 0;
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pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
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PAGE_CACHE_SHIFT;
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struct zone *zone;
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struct pagevec pvec;
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if (mapping->nrpages == 0)
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return;
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pagevec_init(&pvec, 0);
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while (next < end &&
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pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
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int i;
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int pg_scanned = 0;
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zone = NULL;
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for (i = 0; i < pagevec_count(&pvec); i++) {
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struct page *page = pvec.pages[i];
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pgoff_t page_index = page->index;
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struct zone *pagezone = page_zone(page);
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pg_scanned++;
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if (page_index > next)
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next = page_index;
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next++;
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if (pagezone != zone) {
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if (zone)
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spin_unlock_irq(&zone->lru_lock);
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zone = pagezone;
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spin_lock_irq(&zone->lru_lock);
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}
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if (PageLRU(page) && PageUnevictable(page))
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check_move_unevictable_page(page, zone);
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pgscanned++;
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pagezone = page_zone(page);
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if (pagezone != zone) {
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if (zone)
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spin_unlock_irq(&zone->lru_lock);
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zone = pagezone;
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spin_lock_irq(&zone->lru_lock);
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}
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if (zone)
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spin_unlock_irq(&zone->lru_lock);
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pagevec_release(&pvec);
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count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
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cond_resched();
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if (!PageLRU(page) || !PageUnevictable(page))
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continue;
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if (page_evictable(page, NULL)) {
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enum lru_list lru = page_lru_base_type(page);
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VM_BUG_ON(PageActive(page));
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ClearPageUnevictable(page);
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__dec_zone_state(zone, NR_UNEVICTABLE);
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lruvec = mem_cgroup_lru_move_lists(zone, page,
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LRU_UNEVICTABLE, lru);
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list_move(&page->lru, &lruvec->lists[lru]);
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__inc_zone_state(zone, NR_INACTIVE_ANON + lru);
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pgrescued++;
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}
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}
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if (zone) {
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__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
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__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
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spin_unlock_irq(&zone->lru_lock);
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}
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}
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#else
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void scan_mapping_unevictable_pages(struct address_space *mapping)
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{
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}
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#endif /* CONFIG_SHMEM */
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