Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751334AbdH1L3d (ORCPT ); Mon, 28 Aug 2017 07:29:33 -0400 Received: from mx2.suse.de ([195.135.220.15]:41478 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750873AbdH1L3c (ORCPT ); Mon, 28 Aug 2017 07:29:32 -0400 Subject: Re: [PATCH 2/2] mm/slub: don't use reserved highatomic pageblock for optimistic try To: js1304@gmail.com, Andrew Morton Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Michal Hocko References: <1503882675-17910-1-git-send-email-iamjoonsoo.kim@lge.com> <1503882675-17910-2-git-send-email-iamjoonsoo.kim@lge.com> From: Vlastimil Babka Message-ID: Date: Mon, 28 Aug 2017 13:29:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <1503882675-17910-2-git-send-email-iamjoonsoo.kim@lge.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2173 Lines: 52 On 08/28/2017 03:11 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 setting > __GFP_NOMEMALLOC in order to not set ALLOC_HARDER. I wonder if it would be more robust to strip GFP_ATOMIC from alloc_gfp. E.g. __GFP_NOMEMALLOC does seem to prevent ALLOC_HARDER, but not ALLOC_HIGH. Or maybe we should adjust __GFP_NOMEMALLOC implementation and document it more thoroughly? CC Michal Hocko Also, were these 2 patches done via code inspection or you noticed suboptimal behavior which got fixed? Thanks. > Signed-off-by: Joonsoo Kim > --- > mm/slub.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index e1e442c..fd8dd89 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -1579,10 +1579,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) > */ > alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL; > if (oo_order(oo) > oo_order(s->min)) { > - if (alloc_gfp & __GFP_DIRECT_RECLAIM) { > - alloc_gfp |= __GFP_NOMEMALLOC; > - alloc_gfp &= ~__GFP_DIRECT_RECLAIM; > - } > + alloc_gfp |= __GFP_NOMEMALLOC; > + alloc_gfp &= ~__GFP_DIRECT_RECLAIM; > } > > page = alloc_slab_page(s, alloc_gfp, node, oo); >