On Thu, 14 Jul 2011 00:46:43 -0400
Christoph Hellwig [off-list ref] wrote:

On Thu, Jul 14, 2011 at 10:38:01AM +0900, KAMEZAWA Hiroyuki wrote:

quoted

quoted

+			/*
+			 * Only kswapd can writeback filesystem pages to
+			 * avoid risk of stack overflow
+			 */
+			if (page_is_file_cache(page) && !current_is_kswapd()) {
+				inc_zone_page_state(page, NR_VMSCAN_WRITE_SKIP);
+				goto keep_locked;
+			}
+

This will cause tons of memcg OOM kill because we have no help of kswapd (now).

XFS and btrfs already disable writeback from memcg context, as does ext4
for the typical non-overwrite workloads, and none has fallen apart.

In fact there's no way we can enable them as the memcg calling contexts
tend to have massive stack usage.

Hmm, XFS/btrfs adds pages to radix-tree in deep stack ?

Thanks,
-Kame

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