lkml.org 
[lkml]   [2009]   [Apr]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/6] Handle bio_alloc failure
On Tue, Apr 14 2009, Theodore Tso wrote:
> 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.

Read mempool.c:mempool_alloc(). If __GFP_WAIT is set, it'll never turn
without having done the allocation. It's a bit weird that it isn't
documented in bio_alloc() itself, but there are several other places in
bio.c that references the fact that it cannot fail.

> 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.

It's the entire premise of a mempool, so trust me, it'll never go away.
It is the reason they were added in the first place, for eg swap you
need the mempool guarantee or you risk deadlocking.

--
Jens Axboe



\
 
 \ /
  Last update: 2009-04-14 20:45    [W:0.022 / U:14.628 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site