linux-kernel - Re: [PATCH 0/3] Fix malloc() stall in zone_reclaim() and bring behaviour more in line with expectations V3

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Date:	Tue, 16 Jun 2009 21:30:21 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	Christoph Lameter <cl@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>, riel@...hat.com,
	fengguang.wu@...el.com, linuxram@...ibm.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 0/3] Fix malloc() stall in zone_reclaim() and bring behaviour more in line with expectations V3

> On Tue, Jun 16, 2009 at 09:08:47PM +0900, KOSAKI Motohiro wrote:
> > > On Mon, Jun 15, 2009 at 11:01:41AM -0400, Christoph Lameter wrote:
> > > > On Mon, 15 Jun 2009, Mel Gorman wrote:
> > > > 
> > > > > > May I ask your worry?
> > > > > >
> > > > >
> > > > > Simply that I believe the intention of PF_SWAPWRITE here was to allow
> > > > > zone_reclaim() to aggressively reclaim memory if the reclaim_mode allowed
> > > > > it as it was a statement that off-node accesses are really not desired.
> > > > 
> > > > Right.
> > > > 
> > > > > Ok. I am not fully convinced but I'll not block it either if believe it's
> > > > > necessary. My current understanding is that this patch only makes a difference
> > > > > if the server is IO congested in which case the system is struggling anyway
> > > > > and an off-node access is going to be relatively small penalty overall.
> > > > > Conceivably, having PF_SWAPWRITE set makes things worse in that situation
> > > > > and the patch makes some sense.
> > > > 
> > > > We could drop support for RECLAIM_SWAP if that simplifies things.
> > > > 
> > > 
> > > I don't think that is necessary. While I expect it's very rarely used, I
> > > imagine a situation where it would be desirable on a system that had large
> > > amounts of tmpfs pages but where it wasn't critical they remain in-memory.
> > > 
> > > Removing PF_SWAPWRITE would make it less aggressive and if you were
> > > happy with that, then that would be good enough for me.
> > 
> > I surprised this a bit. I've imazined Christoph never agree to remove it.
> > Currently, trouble hitting user of mine don't use this feature. Thus, if it can be
> > removed, I don't need to worry abusing this again and I'm happy.
> > 
> > Mel, Have you seen actual user of this?
> > 
> 
> No, but then again the usage for it is quite specific. Namely for use on
> systems that uses a large amount of tmpfs where the remote NUMA penalty is
> high and it's acceptable to swap tmpfs pages to avoid remote accesses. I
> don't see the harm in having the option available.

ok.
I understand your opinion. 

Thanks.



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