linux-kernel - Re: [v5][PATCH 6/6] mm: vmscan: drain batch list during long operations

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Message-ID: <20130604232315.GA31006@blaptop>
Date:	Wed, 5 Jun 2013 08:23:15 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mgorman@...e.de,
	tim.c.chen@...ux.intel.com
Subject: Re: [v5][PATCH 6/6] mm: vmscan: drain batch list during long
 operations

Hello Dave,

On Tue, Jun 04, 2013 at 08:24:38AM -0700, Dave Hansen wrote:
> On 06/03/2013 11:05 PM, Minchan Kim wrote:
> >> > This ensures that we drain the batch if we are about to perform a
> >> > pageout() or congestion_wait(), either of which will take some
> >> > time.  We expect this to help mitigate the worst of the latency
> >> > increase that the batching could cause.
> > Nice idea but I could see drain before pageout but congestion_wait?
> 
> That comment managed to bitrot a bit :(
> 
> The first version of these had the drain before pageout() only.  Then,
> Mel added a congestion_wait() call, and I modified the series to also
> drain there.  But, some other patches took the congestion_wait() back
> out, so I took that drain back out.

I am looking next-20130530 and it has still a congestion_wait.
I'm confusing. :(


                if (PageWriteback(page)) {
			/* Case 1 above */
			if (current_is_kswapd() &&
			    PageReclaim(page) &&
			    zone_is_reclaim_writeback(zone)) {
				congestion_wait(BLK_RW_ASYNC, HZ/10);
				zone_clear_flag(zone, ZONE_WRITEBACK);
> 
> I _believe_ the only congestion_wait() left in there is a cgroup-related
> one that we didn't think would cause very much harm.

The congestion_wait I am seeing is not cgroup-related one.

I'd like to clear this confusing.
Thanks.

> 
> --
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-- 
Kind regards,
Minchan Kim
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