Re: [PATCH 1/5] mm: vmscan: Do not writeback filesystem pages in direct reclaim

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

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