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authorHugh Dickins <hugh@veritas.com>2007-03-29 01:20:37 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-03-29 08:22:25 -0700
commit16a100190d39592d1d56ff5a0b978b20288c3427 (patch)
tree63af0d78497e540f096262da83ed44ddbe1eab94
parent1ae7000630e3c05b6f7e3dfc76472f1bca6c1788 (diff)
[PATCH] holepunch: fix disconnected pages after second truncate
shmem_truncate_range has its own truncate_inode_pages_range, to free any pages racily instantiated while it was in progress: a SHMEM_PAGEIN flag is set when this might have happened. But holepunching gets no chance to clear that flag at the start of vmtruncate_range, so it's always set (unless a truncate came just before), so holepunch almost always does this second truncate_inode_pages_range. shmem holepunch has unlikely swap<->file races hereabouts whatever we do (without a fuller rework than is fit for this release): I was going to skip the second truncate in the punch_hole case, but Miklos points out that would make holepunch correctness more vulnerable to swapoff. So keep the second truncate, but follow it by an unmap_mapping_range to eliminate the disconnected pages (freed from pagecache while still mapped in userspace) that it might have left behind. Signed-off-by: Hugh Dickins <hugh@veritas.com> Cc: Miklos Szeredi <mszeredi@suse.cz> Cc: Badari Pulavarty <pbadari@us.ibm.com> Cc: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/shmem.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 578eceafba4..b2a35ebf071 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -674,8 +674,16 @@ done2:
* generic_delete_inode did it, before we lowered next_index.
* Also, though shmem_getpage checks i_size before adding to
* cache, no recheck after: so fix the narrow window there too.
+ *
+ * Recalling truncate_inode_pages_range and unmap_mapping_range
+ * every time for punch_hole (which never got a chance to clear
+ * SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
+ * yet hardly ever necessary: try to optimize them out later.
*/
truncate_inode_pages_range(inode->i_mapping, start, end);
+ if (punch_hole)
+ unmap_mapping_range(inode->i_mapping, start,
+ end - start, 1);
}
spin_lock(&info->lock);