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authorEnrik Berkhan <Enrik.Berkhan@ge.com>2009-03-13 13:51:56 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-03-14 11:57:22 -0700
commit020fe22ff14320927f394de222cbb11708bcc7a8 (patch)
tree1445c0134136c4aa84c9cb6aedd3043fae60f167
parent041b62374c7fedc11a8a1eeda2868612d3d1436c (diff)
nommu: ramfs: pages allocated to an inode's pagecache may get wrongly discarded
The pages attached to a ramfs inode's pagecache by truncation from nothing - as done by SYSV SHM for example - may get discarded under memory pressure. The problem is that the pages are not marked dirty. Anything that creates data in an MMU-based ramfs will cause the pages holding that data will cause the set_page_dirty() aop to be called. For the NOMMU-based mmap, set_page_dirty() may be called by write(), but it won't be called by page-writing faults on writable mmaps, and it isn't called by ramfs_nommu_expand_for_mapping() when a file is being truncated from nothing to allocate a contiguous run. The solution is to mark the pages dirty at the point of allocation by the truncation code. Signed-off-by: Enrik Berkhan <Enrik.Berkhan@ge.com> Signed-off-by: David Howells <dhowells@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/ramfs/file-nommu.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
index b9b567a2837..90d72bead55 100644
--- a/fs/ramfs/file-nommu.c
+++ b/fs/ramfs/file-nommu.c
@@ -114,6 +114,9 @@ int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
if (!pagevec_add(&lru_pvec, page))
__pagevec_lru_add_file(&lru_pvec);
+ /* prevent the page from being discarded on memory pressure */
+ SetPageDirty(page);
+
unlock_page(page);
}