[patch] Patch to revert commits

patch (text/plain), 2.82 KB, created by Richard Yao (RETIRED) on 2013-03-17 15:44:03 UTC

Revert memcg patches that prevent OOM with too many dirty pages

This is a monolithic patch that reverts the following commits:

torvalds/linux@c3b94f44fcb0725471ecebb701c077a0ed67bd07
torvalds/linux@e62e384e9da8d9a0c599795464a7e76fd490931c

These changes cause attempts by ZFS to flush dirty pages to deadlock. A precise
explanation is available at the ZFSOnLinux issue tracker:

https://github.com/zfsonlinux/zfs/issues/1342i

I have a fix in development, but it will not be ready for some time. These
patches only benefit kernels built with CONFIG_MEMCG (default N in Kconfig)
when memory cgroups are actually used, are given small quantities of RAM and
have significant disk IO occur in them. As far as I can tell, nothing in the
main tree uses this and the one user on the forums that appears to use memory
cgroups does not use them under conditions that would trigger the issue that
these patches are meant to solve. Reverting these commits is a reasonable
stopgap measure until a fix in ZFS is ready.

Signed-off: Richard Yao <[e-mail]>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 88c5fed..13abf1b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -723,41 +723,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 
 		if (PageWriteback(page)) {
-			/*
-			 * memcg doesn't have any dirty pages throttling so we
-			 * could easily OOM just because too many pages are in
-			 * writeback and there is nothing else to reclaim.
-			 *
-			 * Check __GFP_IO, certainly because a loop driver
-			 * thread might enter reclaim, and deadlock if it waits
-			 * on a page for which it is needed to do the write
-			 * (loop masks off __GFP_IO|__GFP_FS for this reason);
-			 * but more thought would probably show more reasons.
-			 *
-			 * Don't require __GFP_FS, since we're not going into
-			 * the FS, just waiting on its writeback completion.
-			 * Worryingly, ext4 gfs2 and xfs allocate pages with
-			 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
-			 * testing may_enter_fs here is liable to OOM on them.
-			 */
-			if (global_reclaim(sc) ||
-			    !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
-				/*
-				 * This is slightly racy - end_page_writeback()
-				 * might have just cleared PageReclaim, then
-				 * setting PageReclaim here end up interpreted
-				 * as PageReadahead - but that does not matter
-				 * enough to care.  What we do want is for this
-				 * page to have PageReclaim set next time memcg
-				 * reclaim reaches the tests above, so it will
-				 * then wait_on_page_writeback() to avoid OOM;
-				 * and it's also appropriate in global reclaim.
-				 */
-				SetPageReclaim(page);
-				nr_writeback++;
-				goto keep_locked;
-			}
-			wait_on_page_writeback(page);
+			nr_writeback++;
+			unlock_page(page);
+			goto keep;
 		}
 
 		if (!force_reclaim)