linux-kernel - Re: [PATCH 4.5/8] blkcg, cfq-iosched: use GFP_NOWAIT instead of GFP

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Date:	Tue, 09 Jun 2015 10:27:59 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, vgoyal@...hat.com,
	avanzini.arianna@...il.com
Subject: Re: [PATCH 4.5/8] blkcg, cfq-iosched: use GFP_NOWAIT instead of GFP_ATOMIC for non-critical allocations

Tejun Heo <tj@...nel.org> writes:

> From b848495d2c987e960d1f7794966d82c05fcefc6d Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Tue, 9 Jun 2015 13:19:40 +0900
>
> blkcg performs several allocations to track IOs per cgroup and enforce
> resource control.  Most of these allocations are performed lazily on
> demand in the IO path and thus can't involve reclaim path.  Currently,
> these allocations use GFP_ATOMIC; however, blkcg can gracefully deal
> with occassional failures of these allocations by punting IOs to the
> root cgroup and there's no reason to reach into the emergency reserve.
>
> This patch replaces GFP_ATOMIC with GFP_NOWAIT for the following
> allocations.
>
> * bdi_writeback_congested and blkcg_gq allocations in blkg_create().
>
> * radix tree node allocations for blkcg->blkg_tree.
>
> * cfq_queue allocation on ioprio changes.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Suggested-by: Jeff Moyer <jmoyer@...hat.com>
> Suggested-by: Vivek Goyal <vgoyal@...hat.com>

Thanks, Tejun!

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
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