From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752591AbcDZOuO (ORCPT ); Tue, 26 Apr 2016 10:50:14 -0400 Received: from outbound-smtp05.blacknight.com ([81.17.249.38]:58792 "EHLO outbound-smtp05.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752202AbcDZOuK (ORCPT ); Tue, 26 Apr 2016 10:50:10 -0400 Date: Tue, 26 Apr 2016 15:50:06 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Jesper Dangaard Brouer , Linux-MM , LKML Subject: Re: [PATCH 15/28] mm, page_alloc: Move might_sleep_if check to the allocator slowpath Message-ID: <20160426145006.GD2858@techsingularity.net> References: <1460710760-32601-1-git-send-email-mgorman@techsingularity.net> <1460711275-1130-1-git-send-email-mgorman@techsingularity.net> <1460711275-1130-3-git-send-email-mgorman@techsingularity.net> <571F7002.5030602@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <571F7002.5030602@suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 26, 2016 at 03:41:22PM +0200, Vlastimil Babka wrote: > On 04/15/2016 11:07 AM, Mel Gorman wrote: > >There is a debugging check for callers that specify __GFP_DIRECT_RECLAIM > >from a context that cannot sleep. Triggering this is almost certainly > >a bug but it's also overhead in the fast path. > > For CONFIG_DEBUG_ATOMIC_SLEEP, enabling is asking for the overhead. But for > CONFIG_PREEMPT_VOLUNTARY which turns it into _cond_resched(), I guess it's > not. > Either way, it struck me as odd. It does depend on the config and it's marginal so if there is a problem then I can drop it. > >Move the check to the slow > >path. It'll be harder to trigger as it'll only be checked when watermarks > >are depleted but it'll also only be checked in a path that can sleep. > > Hmm what about zone_reclaim_mode=1, should the check be also duplicated to > that part of get_page_from_freelist()? > zone_reclaim has a !gfpflags_allow_blocking() check, does not call cond_resched() before that check so it does not fall into an accidental sleep path. I'm not seeing why the check is necessary there. -- Mel Gorman SUSE Labs