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Date: Tue, 14 Apr 2009 14:33:51 -0400
From: Theodore Tso <tytso@mit.edu>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: Nikanth Karthikesan <knikanth@suse.de>, Neil Brown <neilb@suse.de>,
       linux-kernel@vger.kernel.org, Chris Mason <chris.mason@oracle.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Dave Kleikamp <shaggy@austin.ibm.com>, xfs-masters@oss.sgi.com
Subject: Re: [PATCH 0/6] Handle bio_alloc failure
Message-ID: <20090414183351.GK955@mit.edu>
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	Dave Kleikamp <shaggy@austin.ibm.com>, xfs-masters@oss.sgi.com
References: <200904141636.26557.knikanth@novell.com> <20090414111838.GG5178@kernel.dk> <200904141711.20378.knikanth@suse.de> <20090414181632.GI955@mit.edu> <20090414182049.GI5178@kernel.dk>
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On Tue, Apr 14, 2009 at 08:20:49PM +0200, Jens Axboe wrote:
> 
> It's a bio_alloc() guarantee, it uses a mempool backing. And if you use
> a mempool backing, any allocation that can wait will always be
> satisfied.
> 

Am I missing something?  I don't see anything in
include/linux/mempool.h or mm/mempool.c, or in block/blk-core.c or
include/linux/bio.h which documents that GFP_WAIT implies that
bio_alloc() will always succeed.   

My concern is that at some point in the future, someone either in the
block device layer or in mm/mempool.c will consider this an
implementation detail, and all of sudden calls to bio_alloc() with
GFP_WAIT will start failing and the resulting hilarty which ensues
won't be easily predicted by the developer making this change.

Regards,

					- Ted
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