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

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/5] mm: vmscan: Do not writeback filesystem pages in direct reclaim
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Date: Thu, 14 Jul 2011 13:46:34 +0900
Cc: Mel Gorman <mgorman@xxxxxxx>, Linux-MM <linux-mm@xxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, XFS <xfs@xxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Johannes Weiner <jweiner@xxxxxxxxxx>, Wu Fengguang <fengguang.wu@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Minchan Kim <minchan.kim@xxxxxxxxx>
In-reply-to: <20110714044643.GA3203@xxxxxxxxxxxxx>
Organization: FUJITSU Co. LTD.
References: <1310567487-15367-1-git-send-email-mgorman@xxxxxxx> <1310567487-15367-2-git-send-email-mgorman@xxxxxxx> <20110714103801.83e10fdb.kamezawa.hiroyu@xxxxxxxxxxxxxx> <20110714044643.GA3203@xxxxxxxxxxxxx>
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

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