From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932145AbcELMs1 (ORCPT ); Thu, 12 May 2016 08:48:27 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36126 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751502AbcELMs0 (ORCPT ); Thu, 12 May 2016 08:48:26 -0400 Date: Thu, 12 May 2016 14:48:24 +0200 From: Michal Hocko To: Vlastimil Babka Cc: linux-mm@kvack.org, Andrew Morton , Joonsoo Kim , Rik van Riel , David Rientjes , Mel Gorman , Johannes Weiner , Tetsuo Handa , linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: [RFC 03/13] mm, page_alloc: don't retry initial attempt in slowpath Message-ID: <20160512124823.GI4200@dhcp22.suse.cz> References: <1462865763-22084-1-git-send-email-vbabka@suse.cz> <1462865763-22084-4-git-send-email-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1462865763-22084-4-git-send-email-vbabka@suse.cz> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 10-05-16 09:35:53, Vlastimil Babka wrote: > After __alloc_pages_slowpath() sets up new alloc_flags and wakes up kswapd, it > first tries get_page_from_freelist() with the new alloc_flags, as it may > succeed e.g. due to using min watermark instead of low watermark. This attempt > does not have to be retried on each loop, since direct reclaim, direct > compaction and oom call get_page_from_freelist() themselves. > > This patch therefore moves the initial attempt above the retry label. The > ALLOC_NO_WATERMARKS attempt is kept under retry label as it's special and > should be retried after each loop. Yes this makes code both more clear and more logical > Kswapd wakeups are also done on each retry > to be safe from potential races resulting in kswapd going to sleep while a > process (that may not be able to reclaim by itself) is still looping. I am not sure this is really necessary but it shouldn't be harmful. The comment clarifies the duplicity so we are not risking "cleanups to remove duplicated code" I guess. > Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko > --- > mm/page_alloc.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 91fbf6f95403..7249949d65ca 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3586,16 +3586,23 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > */ > alloc_flags = gfp_to_alloc_flags(gfp_mask); > > -retry: > if (gfp_mask & __GFP_KSWAPD_RECLAIM) > wake_all_kswapds(order, ac); > > - /* This is the last chance, in general, before the goto nopage. */ > + /* > + * The adjusted alloc_flags might result in immediate success, so try > + * that first > + */ > page = get_page_from_freelist(gfp_mask, order, > alloc_flags & ~ALLOC_NO_WATERMARKS, ac); > if (page) > goto got_pg; > > +retry: > + /* Ensure kswapd doesn't accidentaly go to sleep as long as we loop */ > + if (gfp_mask & __GFP_KSWAPD_RECLAIM) > + wake_all_kswapds(order, ac); > + > /* Allocate without watermarks if the context allows */ > if (alloc_flags & ALLOC_NO_WATERMARKS) { > /* > -- > 2.8.2 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Michal Hocko SUSE Labs