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

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 7/7] xfs: Don't use PF_MEMALLOC
From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Date: Wed, 18 Nov 2009 17:56:46 +0900 (JST)
Cc: kosaki.motohiro@xxxxxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>, linux-mm <linux-mm@xxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, xfs-masters@xxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20091117221108.GK9467@xxxxxxxxxxxxxxxx>
References: <20091117162235.3DEB.A69D9226@xxxxxxxxxxxxxx> <20091117221108.GK9467@xxxxxxxxxxxxxxxx>
> 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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