linux-kernel - Re: [patch 1/6] md: remove dependency on __GFP

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Message-ID: <alpine.DEB.2.00.1008231326500.20535@chino.kir.corp.google.com>
Date:	Mon, 23 Aug 2010 13:37:45 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Neil Brown <neilb@...e.de>, Alasdair G Kergon <agk@...hat.com>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/6] md: remove dependency on __GFP_NOFAIL

On Mon, 23 Aug 2010, Andrew Morton wrote:

> > > Hows about you add a helper function
> > > 
> > > 	void *[kmalloc|alloc_page]_retrying_forever_because_i_suck(lots of args)
> > > 
> > > then convert the callsites to use that, then nuke __GFP_NOFAIL?
> > > 
> > 
> > That would only serve as documentation
> 
> Is that bad?
> 

It implies that these calls are special in some way, basically to mean 
we have no sane error handling for failures, when in reality this is only 
a function of the allocation order when the context does not have 
__GFP_FS.  You may as well just add BUG_ON(!nreg) here instead.

I thought my "/* FIXME: this may potentially loop forever */" was 
sufficient to mean that the allocation must succeed independent of the 
page allocator's implementation, but perhaps you find greping for 
[kmalloc|alloc_page.*]_nofail easier?

I'm not sure what flags such a function would be checking for since the 
page allocator determines whether the oom killer is called or not.  If 
current is killed, an order-0 allocation will succeed because of 
TIF_MEMDIE, and if another task is killed, we must still loop waiting for 
the free memory even with __GFP_FS.
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