Re: [PATCH 7/7] xfs: Don't use PF_MEMALLOC

From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs-masters@oss.sgi.com, LKML <linux-kernel@vger.kernel.org>,
	xfs@oss.sgi.com, Christoph Hellwig <hch@infradead.org>,
	linux-mm <linux-mm@kvack.org>,
	kosaki.motohiro@jp.fujitsu.com, linux-fsdevel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 7/7] xfs: Don't use PF_MEMALLOC
Date: Wed, 18 Nov 2009 17:56:46 +0900 (JST)	[thread overview]
Message-ID: <20091118153302.3E20.A69D9226@jp.fujitsu.com> (raw)
In-Reply-To: <20091117221108.GK9467@discord.disaster>

> On Tue, Nov 17, 2009 at 04:23:43PM +0900, KOSAKI Motohiro wrote:
> > 
> > Non MM subsystem must not use PF_MEMALLOC. Memory reclaim need few
> > memory, anyone must not prevent it. Otherwise the system cause
> > mysterious hang-up and/or OOM Killer invokation.
> 
> The xfsbufd is a woken run by a registered memory shaker. i.e. it
> runs when the system needs to reclaim memory. It forceѕ the
> delayed write metadata buffers (of which there can be a lot) to disk
> so that they can be reclaimed on IO completion. This IO submission
> may require ѕome memory to be allocated to be able to free that
> memory.
> 
> Hence, AFAICT the use of PF_MEMALLOC is valid here.

Thanks a lot. 
I have one additional question, may I ask you?

How can we calculate maximum memory usage in xfsbufd?
I'm afraid that VM and XFS works properly but adding two makes memory exhaust.

And, I conclude XFS doesn't need sharing reservation memory with VM,
it only need non failed allocation. right? IOW I'm prefer perter's
suggestion.

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