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-rw-r--r--mm/shmem.c15
1 files changed, 15 insertions, 0 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 404e53bb212..253d205914b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -915,6 +915,21 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
struct inode *inode;
BUG_ON(!PageLocked(page));
+ /*
+ * shmem_backing_dev_info's capabilities prevent regular writeback or
+ * sync from ever calling shmem_writepage; but a stacking filesystem
+ * may use the ->writepage of its underlying filesystem, in which case
+ * we want to do nothing when that underlying filesystem is tmpfs
+ * (writing out to swap is useful as a response to memory pressure, but
+ * of no use to stabilize the data) - just redirty the page, unlock it
+ * and claim success in this case. AOP_WRITEPAGE_ACTIVATE, and the
+ * page_mapped check below, must be avoided unless we're in reclaim.
+ */
+ if (!wbc->for_reclaim) {
+ set_page_dirty(page);
+ unlock_page(page);
+ return 0;
+ }
BUG_ON(page_mapped(page));
mapping = page->mapping;