From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 1F1126B025F for ; Mon, 28 Aug 2017 07:29:33 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id m85so263789wma.8 for ; Mon, 28 Aug 2017 04:29:33 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id t21si132449wme.159.2017.08.28.04.29.31 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 28 Aug 2017 04:29:31 -0700 (PDT) Subject: Re: [PATCH 2/2] mm/slub: don't use reserved highatomic pageblock for optimistic try 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 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: owner-linux-mm@kvack.org List-ID: 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 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); > -- 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