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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>]

On Thu, 14 Jul 2011 00:46:43 -0400
Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:

> 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.
> 

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

Thanks,
-Kame