The patch titled
nommu: ramfs: pages allocated to an inode's pagecache may get wrongly discarded
has been added to the -mm tree. Its filename is
nommu-ramfs-pages-allocated-to-an-inodes-pagecache-may-get-wrongly-discarded.patch
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------------------------------------------------------
Subject: nommu: ramfs: pages allocated to an inode's pagecache may get wrongly discarded
From: Enrik Berkhan <Enrik.Berkhan@xxxxxx>
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@xxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ramfs/file-nommu.c | 3 +++
1 file changed, 3 insertions(+)
diff -puN fs/ramfs/file-nommu.c~nommu-ramfs-pages-allocated-to-an-inodes-pagecache-may-get-wrongly-discarded fs/ramfs/file-nommu.c
--- a/fs/ramfs/file-nommu.c~nommu-ramfs-pages-allocated-to-an-inodes-pagecache-may-get-wrongly-discarded
+++ a/fs/ramfs/file-nommu.c
@@ -113,6 +113,9 @@ int ramfs_nommu_expand_for_mapping(struc
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);
}
_
Patches currently in -mm which might be from Enrik.Berkhan@xxxxxx are
origin.patch
nommu-ramfs-pages-allocated-to-an-inodes-pagecache-may-get-wrongly-discarded.patch
nommu-ramfs-pages-allocated-to-an-inodes-pagecache-may-get-wrongly-discarded-fix.patch
nommu-ramfs-dont-leak-pages-when-adding-to-page-cache-fails.patch
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