linux-kernel - Re: [PATCH 0/6] Handle bio

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Date:	Tue, 14 Apr 2009 14:33:51 -0400
From:	Theodore Tso <tytso@....edu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Nikanth Karthikesan <knikanth@...e.de>, Neil Brown <neilb@...e.de>,
	linux-kernel@...r.kernel.org, Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Kleikamp <shaggy@...tin.ibm.com>, xfs-masters@....sgi.com
Subject: Re: [PATCH 0/6] Handle bio_alloc failure

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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