linux-kernel - Re: [RFC 1/1] fs/reiserfs/journal.c: Remove obsolete __GFP

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Date:	Wed, 26 Mar 2014 21:38:40 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	tytso@....edu
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	Fabian Frederick <fabf@...net.be>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	reiserfs-devel@...r.kernel.org, Joe Perches <joe@...ches.com>
Subject: Re: [RFC 1/1] fs/reiserfs/journal.c: Remove obsolete  __GFP_NOFAIL

On Wed, 26 Mar 2014, tytso@....edu wrote:

> But that's another new user of GFP_NOFAIL (and one added three years
> after David tried to declare There Shalt Be No New Users of
> GFP_NOFAIL), and sure, we could probably patch around that by having
> places where there's no other alternaive to keep a preallocated batch
> of pages and/or allocated structures at each code site.  But that's as
> bad as looping at each code site; in fact, wouldn't it be better if
> the allocator wants to avoid looping, to have a separate batch of
> pages which (ala GFP_ATOMIC) which is reserved for just for GFP_NOFAIL
> allocations when all else fails?
> 

I didn't declare nobody should be adding __GFP_NOFAIL three years ago, 
rather three months ago I proposed a patch to fix __GFP_NOFAIL for 
GFP_ATOMIC allocations you're talking about above since, guess what, 
GPF_ATOMIC | __GFP_NOFAIL today easily returns NULL.  I tried fixing that 
failable-__GFP_NOFAIL problem with 
http://marc.info/?l=linux-kernel&m=138662620812698 but Andrew requested a 
WARN_ON_ONCE() instead since nobody is currently doing that and we agreed 
to warn against new users.

So we should either return to my earlier patch to actually make 
__GFP_NOFAIL not fail, or improve (but not remove) the checkpatch warning 
for these failable cases.  I couldn't care less if we add 5,000 new 
__GFP_NOFAIL users tomorrow, I just care that it does what is expected if 
people are going to be adding them.
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