linux-ext4 - Re: [patch 1/5] mm: add nofail variants of kmalloc kcalloc and kzalloc

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Date:	Wed, 25 Aug 2010 17:30:42 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Ted Ts'o" <tytso@....edu>, Peter Zijlstra <peterz@...radead.org>,
	Jens Axboe <jaxboe@...ionio.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Brown <neilb@...e.de>, Alasdair G Kergon <agk@...hat.com>,
	Chris Mason <chris.mason@...cle.com>,
	Steven Whitehouse <swhiteho@...hat.com>,
	Jan Kara <jack@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
	"cluster-devel@...hat.com" <cluster-devel@...hat.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"reiserfs-devel@...r.kernel.org" <reiserfs-devel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/5] mm: add nofail variants of kmalloc kcalloc and
 kzalloc

On Wed, 25 Aug 2010, Ted Ts'o wrote:

> > I'll repropose the patchset with __deprecated as you suggested.  Thanks!
> 
> And what Dave and I are saying is that we'll either need to do our on
> loop to avoid the deprecation warning, or the use of the deprecated
> function will probably be used forever...
> 

We certainly hope that nobody will reimplement the same function without 
the __deprecated warning, especially for order < PAGE_ALLOC_COSTLY_ORDER 
where there's no looping at a higher level.  So perhaps the best 
alternative is to implement the same _nofail() functions but do a 
WARN_ON(get_order(size) > PAGE_ALLOC_COSTLY_ORDER) instead?

I think it's really sad that the caller can't know what the upper bounds 
of its memory requirement are ahead of time or at least be able to 
implement a memory freeing function when kmalloc() returns NULL.
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