Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752496AbdIFJUU (ORCPT ); Wed, 6 Sep 2017 05:20:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:55484 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752325AbdIFJUS (ORCPT ); Wed, 6 Sep 2017 05:20:18 -0400 Date: Wed, 6 Sep 2017 11:20:14 +0200 From: Michal Hocko To: Vlastimil Babka Cc: js1304@gmail.com, Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Joonsoo Kim Subject: Re: [PATCH 2/2] mm/slub: don't use reserved memory for optimistic try Message-ID: <20170906092014.6z73x5mfxn32lbg6@dhcp22.suse.cz> References: <1504672666-19682-1-git-send-email-iamjoonsoo.kim@lge.com> <1504672666-19682-2-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2885 Lines: 72 On Wed 06-09-17 10:10:22, Vlastimil Babka wrote: > On 09/06/2017 06:37 AM, js1304@gmail.com wrote: > > From: Joonsoo Kim > > > > High-order atomic allocation is difficult to succeed since we cannot > > reclaim anything in this context. So, we reserves the pageblock for > > this kind of request. > > > > In slub, we try to allocate higher-order page more than it actually > > needs in order to get the best performance. If this optimistic try is > > used with GFP_ATOMIC, alloc_flags will be set as ALLOC_HARDER and > > the pageblock reserved for high-order atomic allocation would be used. > > Moreover, this request would reserve the MIGRATE_HIGHATOMIC pageblock > > ,if succeed, to prepare further request. It would not be good to use > > MIGRATE_HIGHATOMIC pageblock in terms of fragmentation management > > since it unconditionally set a migratetype to request's migratetype > > when unreserving the pageblock without considering the migratetype of > > used pages in the pageblock. > > > > This is not what we don't intend so fix it by unconditionally masking > > out __GFP_ATOMIC in order to not set ALLOC_HARDER. > > > > And, it is also undesirable to use reserved memory for optimistic try > > so mask out __GFP_HIGH. This patch also adds __GFP_NOMEMALLOC since > > we don't want to use the reserved memory for optimistic try even if > > the user has PF_MEMALLOC flag. > > > > Signed-off-by: Joonsoo Kim > > --- > > include/linux/gfp.h | 1 + > > mm/page_alloc.c | 8 ++++++++ > > mm/slub.c | 6 ++---- > > 3 files changed, 11 insertions(+), 4 deletions(-) > > > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > > index f780718..1f5658e 100644 > > --- a/include/linux/gfp.h > > +++ b/include/linux/gfp.h > > @@ -568,6 +568,7 @@ extern gfp_t gfp_allowed_mask; > > > > /* Returns true if the gfp_mask allows use of ALLOC_NO_WATERMARK */ > > bool gfp_pfmemalloc_allowed(gfp_t gfp_mask); > > +gfp_t gfp_drop_reserves(gfp_t gfp_mask); > > > > extern void pm_restrict_gfp_mask(void); > > extern void pm_restore_gfp_mask(void); > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 6dbc49e..0f34356 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -3720,6 +3720,14 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask) > > return !!__gfp_pfmemalloc_flags(gfp_mask); > > } > > > > +gfp_t gfp_drop_reserves(gfp_t gfp_mask) > > +{ > > + gfp_mask &= ~(__GFP_HIGH | __GFP_ATOMIC); > > + gfp_mask |= __GFP_NOMEMALLOC; > > + > > + return gfp_mask; > > +} > > + > > I think it's wasteful to do a function call for this, inline definition > in header would be better (gfp_pfmemalloc_allowed() is different as it > relies on a rather heavyweight __gfp_pfmemalloc_flags(). Agreed. If you do that, feel free to add Acked-by: Michal Hocko -- Michal Hocko SUSE Labs