We had thought that pages could no longer get freed while still marked as
mlocked; but Johannes Weiner posted this program to demonstrate that
truncating an mlocked private file mapping containing COWed pages is still
mishandled:
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
int main(void)
{
char *map;
int fd;
system("grep mlockfreed /proc/vmstat");
fd = open("chigurh", O_CREAT|O_EXCL|O_RDWR);
unlink("chigurh");
ftruncate(fd, 4096);
map = mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE, fd, 0);
map[0] = 11;
mlock(map, sizeof(fd));
ftruncate(fd, 0);
close(fd);
munlock(map, sizeof(fd));
munmap(map, 4096);
system("grep mlockfreed /proc/vmstat");
return 0;
}
The anon COWed pages are not caught by truncation's clear_page_mlock() of
the pagecache pages; but unmap_mapping_range() unmaps them, so we ought to
look out for them there in page_remove_rmap(). Indeed, why should
truncation or invalidation be doing the clear_page_mlock() when removing
from pagecache? mlock is a property of mapping in userspace, not a
property of pagecache: an mlocked unmapped page is nonsensical.
Reported-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Rik van Riel <riel@redhat.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ying Han <yinghan@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* If called for a page that is still mapped by mlocked vmas, all we do
* is revert to lazy LRU behaviour -- semantics are not broken.
*/
* If called for a page that is still mapped by mlocked vmas, all we do
* is revert to lazy LRU behaviour -- semantics are not broken.
*/
-extern void __clear_page_mlock(struct page *page);
-static inline void clear_page_mlock(struct page *page)
-{
- if (unlikely(TestClearPageMlocked(page)))
- __clear_page_mlock(page);
-}
+extern void clear_page_mlock(struct page *page);
/*
* mlock_migrate_page - called only from migrate_page_copy() to
/*
* mlock_migrate_page - called only from migrate_page_copy() to
if (page->mapping && trylock_page(page)) {
lru_add_drain(); /* push cached pages to LRU */
/*
if (page->mapping && trylock_page(page)) {
lru_add_drain(); /* push cached pages to LRU */
/*
- * Because we lock page here and migration is
- * blocked by the pte's page reference, we need
- * only check for file-cache page truncation.
+ * Because we lock page here, and migration is
+ * blocked by the pte's page reference, and we
+ * know the page is still mapped, we don't even
+ * need to check for file-cache page truncation.
- if (page->mapping)
- mlock_vma_page(page);
/*
* LRU accounting for clear_page_mlock()
*/
/*
* LRU accounting for clear_page_mlock()
*/
-void __clear_page_mlock(struct page *page)
+void clear_page_mlock(struct page *page)
- VM_BUG_ON(!PageLocked(page));
-
- if (!page->mapping) { /* truncated ? */
+ if (!TestClearPageMlocked(page))
dec_zone_page_state(page, NR_MLOCK);
count_vm_event(UNEVICTABLE_PGCLEARED);
dec_zone_page_state(page, NR_MLOCK);
count_vm_event(UNEVICTABLE_PGCLEARED);
page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
if (page && !IS_ERR(page)) {
lock_page(page);
page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
if (page && !IS_ERR(page)) {
lock_page(page);
- /*
- * Like in __mlock_vma_pages_range(),
- * because we lock page here and migration is
- * blocked by the elevated reference, we need
- * only check for file-cache page truncation.
- */
- if (page->mapping)
- munlock_vma_page(page);
+ munlock_vma_page(page);
unlock_page(page);
put_page(page);
}
unlock_page(page);
put_page(page);
}
} else {
__dec_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
} else {
__dec_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
+ mem_cgroup_end_update_page_stat(page, &locked, &flags);
+ if (unlikely(PageMlocked(page)))
+ clear_page_mlock(page);
/*
* It would be tidy to reset the PageAnon mapping here,
* but that might overwrite a racing page_add_anon_rmap
/*
* It would be tidy to reset the PageAnon mapping here,
* but that might overwrite a racing page_add_anon_rmap
* Leaving it set also helps swapoff to reinstate ptes
* faster for those pages still in swapcache.
*/
* Leaving it set also helps swapoff to reinstate ptes
* faster for those pages still in swapcache.
*/
out:
if (!anon)
mem_cgroup_end_update_page_stat(page, &locked, &flags);
out:
if (!anon)
mem_cgroup_end_update_page_stat(page, &locked, &flags);
cancel_dirty_page(page, PAGE_CACHE_SIZE);
cancel_dirty_page(page, PAGE_CACHE_SIZE);
- clear_page_mlock(page);
ClearPageMappedToDisk(page);
delete_from_page_cache(page);
return 0;
ClearPageMappedToDisk(page);
delete_from_page_cache(page);
return 0;
if (page_has_private(page) && !try_to_release_page(page, 0))
return 0;
if (page_has_private(page) && !try_to_release_page(page, 0))
return 0;
- clear_page_mlock(page);
ret = remove_mapping(mapping, page);
return ret;
ret = remove_mapping(mapping, page);
return ret;
if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;
if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;
- clear_page_mlock(page);
-
spin_lock_irq(&mapping->tree_lock);
if (PageDirty(page))
goto failed;
spin_lock_irq(&mapping->tree_lock);
if (PageDirty(page))
goto failed;