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authorHugh Dickins <hugh@veritas.com>2007-04-13 18:27:10 +0100
committerGreg Kroah-Hartman <gregkh@suse.de>2007-05-01 17:05:55 -0700
commit42988ea6a81e888a6aa28549071e00400b68f4f7 (patch)
parent32576fd4ae53e17af4ca814f7876372a96266b37 (diff)
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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
1 files changed, 8 insertions, 0 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 265b41617a7d..fc30c59aa7d0 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);