linux-kernel - Re: [PATCH 02/11] blkcg: __blkg_lookup_create() doesn't have to fail on radix tree preload failure

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Message-ID: <20120427144709.GJ27486@google.com>
Date:	Fri, 27 Apr 2012 07:47:09 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, ctalbott@...gle.com, rni@...gle.com,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	containers@...ts.linux-foundation.org, fengguang.wu@...el.com,
	hughd@...gle.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 02/11] blkcg: __blkg_lookup_create() doesn't have to
 fail on radix tree preload failure

Hello,

On Fri, Apr 27, 2012 at 10:42:58AM -0400, Vivek Goyal wrote:
> On Thu, Apr 26, 2012 at 02:59:12PM -0700, Tejun Heo wrote:
> > __blkg_lookup_create() currently fails if radix_tree_preload() fails;
> > however, preload failrue doesn't imply insertion failure.  Don't fail
> > __blkg_lookup_create() on preload failure.
> > 
> 
> If we are going to try the insertion anyway irrespective of the fact
> whether preload succeeded or not, they why call radix_tree_preload()
> at all? How does that help?

Hmmm... it seems I originally misread radix_tree_node_alloc() - I
thought it didn't go through kmem_cache_alloc() if gfp_mask didn't
contain __GFP_WAIT.  If we don't use more permissible GFP flag during
preloading there's no point in preloading.  Will drop it.

Thanks.

-- 
tejun
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