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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 2012-01-20 14:34:21 -08:00 committed by Linus Torvalds
parent 85046579bd
commit 245132643e
5 changed files with 85 additions and 98 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/shmem_fs.h
View File

@ -48,6 +48,7 @@ extern struct file *shmem_file_setup(const char *name,
loff_t size, unsigned long flags);
extern int shmem_zero_setup(struct vm_area_struct *);
extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
extern void shmem_unlock_mapping(struct address_space *mapping);
extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);

2
include/linux/swap.h
View File

@ -273,7 +273,7 @@ static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
#endif
extern int page_evictable(struct page *page, struct vm_area_struct *vma);
extern void scan_mapping_unevictable_pages(struct address_space *);
extern void check_move_unevictable_pages(struct page **, int nr_pages);
extern unsigned long scan_unevictable_pages;
extern int scan_unevictable_handler(struct ctl_table *, int,

2
ipc/shm.c
View File

@ -916,7 +916,7 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
shp->mlock_user = NULL;
get_file(shm_file);
shm_unlock(shp);
scan_mapping_unevictable_pages(shm_file->f_mapping);
shmem_unlock_mapping(shm_file->f_mapping);
fput(shm_file);
goto out;
}

46
mm/shmem.c
View File

@ -379,7 +379,7 @@ static int shmem_free_swap(struct address_space *mapping,
/*
* Pagevec may contain swap entries, so shuffle up pages before releasing.
*/
static void shmem_pagevec_release(struct pagevec *pvec)
static void shmem_deswap_pagevec(struct pagevec *pvec)
{
int i, j;
@ -389,7 +389,36 @@ static void shmem_pagevec_release(struct pagevec *pvec)
pvec->pages[j++] = page;
}
pvec->nr = j;
pagevec_release(pvec);
}
/*
* SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
*/
void shmem_unlock_mapping(struct address_space *mapping)
{
struct pagevec pvec;
pgoff_t indices[PAGEVEC_SIZE];
pgoff_t index = 0;
pagevec_init(&pvec, 0);
/*
* Minor point, but we might as well stop if someone else SHM_LOCKs it.
*/
while (!mapping_unevictable(mapping)) {
/*
* Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
* has finished, if it hits a row of PAGEVEC_SIZE swap entries.
*/
pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
PAGEVEC_SIZE, pvec.pages, indices);
if (!pvec.nr)
break;
index = indices[pvec.nr - 1] + 1;
shmem_deswap_pagevec(&pvec);
check_move_unevictable_pages(pvec.pages, pvec.nr);
pagevec_release(&pvec);
cond_resched();
}
}
/*
@ -440,7 +469,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
}
unlock_page(page);
}
shmem_pagevec_release(&pvec);
shmem_deswap_pagevec(&pvec);
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
cond_resched();
index++;
@ -470,7 +500,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
continue;
}
if (index == start && indices[0] > end) {
shmem_pagevec_release(&pvec);
shmem_deswap_pagevec(&pvec);
pagevec_release(&pvec);
break;
}
mem_cgroup_uncharge_start();
@ -494,7 +525,8 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
}
unlock_page(page);
}
shmem_pagevec_release(&pvec);
shmem_deswap_pagevec(&pvec);
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
index++;
}
@ -2438,6 +2470,10 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
return 0;
}
void shmem_unlock_mapping(struct address_space *mapping)
{
}
void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
truncate_inode_pages_range(inode->i_mapping, lstart, lend);

132
mm/vmscan.c
View File

@ -26,7 +26,6 @@
#include <linux/buffer_head.h> /* for try_to_release_page(),
buffer_heads_over_limit */
#include <linux/mm_inline.h>
#include <linux/pagevec.h>
#include <linux/backing-dev.h>
#include <linux/rmap.h>
#include <linux/topology.h>
@ -661,7 +660,7 @@ redo:
* When racing with an mlock or AS_UNEVICTABLE clearing
* (page is unlocked) make sure that if the other thread
* does not observe our setting of PG_lru and fails
* isolation/check_move_unevictable_page,
* isolation/check_move_unevictable_pages,
* we see PG_mlocked/AS_UNEVICTABLE cleared below and move
* the page back to the evictable list.
*
@ -3501,106 +3500,57 @@ int page_evictable(struct page *page, struct vm_area_struct *vma)
#ifdef CONFIG_SHMEM
/**
* check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
* @page: page to check evictability and move to appropriate lru list
* @zone: zone page is in
* check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
* @pages: array of pages to check
* @nr_pages: number of pages to check
*
* Checks a page for evictability and moves the page to the appropriate
* zone lru list.
*
* Restrictions: zone->lru_lock must be held, page must be on LRU and must
* have PageUnevictable set.
* Checks pages for evictability and moves them to the appropriate lru list.
*
* This function is only used for SysV IPC SHM_UNLOCK.
*/
static void check_move_unevictable_page(struct page *page, struct zone *zone)
void check_move_unevictable_pages(struct page **pages, int nr_pages)
{
struct lruvec *lruvec;
struct zone *zone = NULL;
int pgscanned = 0;
int pgrescued = 0;
int i;
VM_BUG_ON(PageActive(page));
retry:
ClearPageUnevictable(page);
if (page_evictable(page, NULL)) {
enum lru_list l = page_lru_base_type(page);
for (i = 0; i < nr_pages; i++) {
struct page *page = pages[i];
struct zone *pagezone;
__dec_zone_state(zone, NR_UNEVICTABLE);
lruvec = mem_cgroup_lru_move_lists(zone, page,
LRU_UNEVICTABLE, l);
list_move(&page->lru, &lruvec->lists[l]);
__inc_zone_state(zone, NR_INACTIVE_ANON + l);
__count_vm_event(UNEVICTABLE_PGRESCUED);
} else {
/*
* rotate unevictable list
*/
SetPageUnevictable(page);
lruvec = mem_cgroup_lru_move_lists(zone, page, LRU_UNEVICTABLE,
LRU_UNEVICTABLE);
list_move(&page->lru, &lruvec->lists[LRU_UNEVICTABLE]);
if (page_evictable(page, NULL))
goto retry;
}
}
/**
* scan_mapping_unevictable_pages - scan an address space for evictable pages
* @mapping: struct address_space to scan for evictable pages
*
* Scan all pages in mapping. Check unevictable pages for
* evictability and move them to the appropriate zone lru list.
*
* This function is only used for SysV IPC SHM_UNLOCK.
*/
void scan_mapping_unevictable_pages(struct address_space *mapping)
{
pgoff_t next = 0;
pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
PAGE_CACHE_SHIFT;
struct zone *zone;
struct pagevec pvec;
if (mapping->nrpages == 0)
return;
pagevec_init(&pvec, 0);
while (next < end &&
pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
int i;
int pg_scanned = 0;
zone = NULL;
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
pgoff_t page_index = page->index;
struct zone *pagezone = page_zone(page);
pg_scanned++;
if (page_index > next)
next = page_index;
next++;
if (pagezone != zone) {
if (zone)
spin_unlock_irq(&zone->lru_lock);
zone = pagezone;
spin_lock_irq(&zone->lru_lock);
}
if (PageLRU(page) && PageUnevictable(page))
check_move_unevictable_page(page, zone);
pgscanned++;
pagezone = page_zone(page);
if (pagezone != zone) {
if (zone)
spin_unlock_irq(&zone->lru_lock);
zone = pagezone;
spin_lock_irq(&zone->lru_lock);
}
if (zone)
spin_unlock_irq(&zone->lru_lock);
pagevec_release(&pvec);
count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
cond_resched();
if (!PageLRU(page) || !PageUnevictable(page))
continue;
if (page_evictable(page, NULL)) {
enum lru_list lru = page_lru_base_type(page);
VM_BUG_ON(PageActive(page));
ClearPageUnevictable(page);
__dec_zone_state(zone, NR_UNEVICTABLE);
lruvec = mem_cgroup_lru_move_lists(zone, page,
LRU_UNEVICTABLE, lru);
list_move(&page->lru, &lruvec->lists[lru]);
__inc_zone_state(zone, NR_INACTIVE_ANON + lru);
pgrescued++;
}
}
if (zone) {
__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
spin_unlock_irq(&zone->lru_lock);
}
}
#else
void scan_mapping_unevictable_pages(struct address_space *mapping)
{
}
#endif /* CONFIG_SHMEM */