From 020fe22ff14320927f394de222cbb11708bcc7a8 Mon Sep 17 00:00:00 2001 From: Enrik Berkhan Date: Fri, 13 Mar 2009 13:51:56 -0700 Subject: 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 Signed-off-by: David Howells Cc: Peter Zijlstra Cc: Nick Piggin Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/ramfs/file-nommu.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c index b9b567a28376..90d72bead55b 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); } -- cgit v1.2.3