linux-kernel - Re: [PATCH 2/2] udf: reduce stack usage of udf_get

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Message-Id: <20081119093515.9c807f71.akpm@linux-foundation.org>
Date:	Wed, 19 Nov 2008 09:35:15 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Marcin Slusarz <marcin.slusarz@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] udf: reduce stack usage of udf_get_filename

On Wed, 19 Nov 2008 16:26:22 +0100 Jan Kara <jack@...e.cz> wrote:

> On Tue 18-11-08 16:19:38, Andrew Morton wrote:
> > On Sun, 16 Nov 2008 19:02:45 +0100
> > Marcin Slusarz <marcin.slusarz@...il.com> wrote:
> > 
> > > +	filename = kmalloc(sizeof(struct ustr), GFP_NOFS);
> > 
> > I suspect that we could have used the superior GFP_KERNEL everywhere in
> > both these patches.  But I'll let Jan worry about that ;)
>   Definitely not in the second case - that one is called from inside
> readdir, lookup and symlink resolution code so that could lead to deadlocks
> IMHO.
>   Regarding the first case in process_sequence, that is called only from
> udf_fill_super(). So there it might be safe to use GFP_KERNEL but I'm not
> quite sure either... So I'd leave GFP_NOFS there.
> 

The reason for using GFP_NOFS is to prevent deadlocks when direct
memory reclaim reenters the filesystem code.  But I don't think there's
ever a case when direct reclaim would enter the namespace part of a
filesystem - it is only expected to touch the pagecache (ie: data)
operations: writepage(), block allocator, etc.


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