linux-kernel - Re: [PATCH 0/7] Kill PF

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Date:	Wed, 18 Nov 2009 14:55:51 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	David Rientjes <rientjes@...gle.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/7] Kill PF_MEMALLOC abuse

> On Tue, 2009-11-17 at 17:33 +0900, KOSAKI Motohiro wrote:
> > 
> > if there is so such reason. we might need to implement another MM trick.
> > but keeping this strage usage is not a option. All memory freeing activity
> > (e.g. page out, task killing) need some memory. we need to protect its
> > emergency memory. otherwise linux reliability decrease dramatically when
> > the system face to memory stress. 
> 
> In general PF_MEMALLOC is a particularly bad idea, even for the VM when
> not coupled with limiting the consumption. That is one should make an
> upper-bound estimation of the memory needed for a writeout-path per
> page, and reserve a small multiple thereof, and limit the number of
> pages written out so as to never exceed this estimate.
> 
> If the current mempool interface isn't sufficient (not hard to imagine),
> look at the swap over NFS patch-set, that includes a much more able
> reservation scheme, and accounting framework.

Yes, I agree.

In this discussion, some people explained why their subsystem need
emergency memory, but nobody claim sharing memory pool against VM and
surely want to stop reclaim (PF_MEMALLOC's big side effect).

OK. I try to review your patch carefully and remake this patch series on top
your reservation framework in swap-over-nfs patch series.



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