[PATCH 2/2] SHM_UNLOCK: fix Unevictable pages stranded after swap
From: Hugh Dickins
Date: Fri Jan 06 2012 - 16:12:12 EST
Commit cc39c6a9bbde "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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx [back to 3.1 but will need respins]
---
This version of the patch spun to apply on top of mmotm.
include/linux/shmem_fs.h | 1
include/linux/swap.h | 2
ipc/shm.c | 2
mm/shmem.c | 46 +++++++++++--
mm/vmscan.c | 128 +++++++++++--------------------------
5 files changed, 83 insertions(+), 96 deletions(-)
--- mmotm.orig/include/linux/shmem_fs.h 2012-01-06 09:55:50.901928800 -0800
+++ mmotm/include/linux/shmem_fs.h 2012-01-06 10:10:15.645949349 -0800
@@ -48,6 +48,7 @@ extern struct file *shmem_file_setup(con
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);
--- mmotm.orig/include/linux/swap.h 2012-01-06 09:55:50.901928800 -0800
+++ mmotm/include/linux/swap.h 2012-01-06 10:10:15.645949349 -0800
@@ -279,7 +279,7 @@ static inline int zone_reclaim(struct zo
#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,
--- mmotm.orig/ipc/shm.c 2012-01-06 10:06:13.937943603 -0800
+++ mmotm/ipc/shm.c 2012-01-06 10:10:15.649949348 -0800
@@ -916,7 +916,7 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int,
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;
}
--- mmotm.orig/mm/shmem.c 2012-01-06 10:08:05.505947516 -0800
+++ mmotm/mm/shmem.c 2012-01-06 10:10:15.649949348 -0800
@@ -379,7 +379,7 @@ static int shmem_free_swap(struct addres
/*
* 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
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 *
}
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 *
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 *
}
unlock_page(page);
}
- shmem_pagevec_release(&pvec);
+ shmem_deswap_pagevec(&pvec);
+ pagevec_release(&pvec);
mem_cgroup_uncharge_end();
index++;
}
@@ -2439,6 +2471,10 @@ int shmem_lock(struct file *file, int lo
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);
--- mmotm.orig/mm/vmscan.c 2012-01-06 10:06:13.941943604 -0800
+++ mmotm/mm/vmscan.c 2012-01-06 10:10:15.649949348 -0800
@@ -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.
*
@@ -3501,107 +3500,58 @@ int page_evictable(struct page *page, st
#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);
-
- __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;
+ for (i = 0; i < nr_pages; i++) {
+ struct page *page = pages[i];
+ struct zone *pagezone;
+
+ 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 (mapping->nrpages == 0)
- return;
+ if (!PageLRU(page) || !PageUnevictable(page))
+ continue;
- 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 (page_evictable(page, NULL)) {
+ enum lru_list lru = page_lru_base_type(page);
- if (PageLRU(page) && PageUnevictable(page))
- check_move_unevictable_page(page, zone);
+ 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)
- spin_unlock_irq(&zone->lru_lock);
- pagevec_release(&pvec);
+ }
- count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
- cond_resched();
+ 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 */
static void warn_scan_unevictable_pages(void)
--
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