From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 02958831F4 for ; Thu, 18 May 2017 10:09:33 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id g12so9523489wrg.15 for ; Thu, 18 May 2017 07:09:32 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e36si5109871eda.29.2017.05.18.07.09.31 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 18 May 2017 07:09:31 -0700 (PDT) Subject: Re: [PATCH] mm: clarify why we want kmalloc before falling backto vmallock References: <20170517080932.21423-1-mhocko@kernel.org> From: Vlastimil Babka Message-ID: <9e50d756-4fed-3617-ab93-8298d7e0231b@suse.cz> Date: Thu, 18 May 2017 16:08:58 +0200 MIME-Version: 1.0 In-Reply-To: <20170517080932.21423-1-mhocko@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Andrew Morton Cc: Chris Wilson , linux-mm@kvack.org, LKML , Michal Hocko On 05/17/2017 10:09 AM, Michal Hocko wrote: > From: Michal Hocko > > While converting drm_[cm]alloc* helpers to kvmalloc* variants Chris > Wilson has wondered why we want to try kmalloc before vmalloc fallback > even for larger allocations requests. Let's clarify that one larger > physically contiguous block is less likely to fragment memory than many > scattered pages which can prevent more large blocks from being created. > > Suggested-by: Chris Wilson > Signed-off-by: Michal Hocko Acked-by: Vlastimil Babka > --- > mm/util.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/util.c b/mm/util.c > index 464df3489903..87499f8119f2 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -357,7 +357,10 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node) > WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL); > > /* > - * Make sure that larger requests are not too disruptive - no OOM > + * We want to attempt a large physically contiguous block first because > + * it is less likely to fragment multiple larger blocks and therefore > + * contribute to a long term fragmentation less than vmalloc fallback. > + * However make sure that larger requests are not too disruptive - no OOM > * killer and no allocation failure warnings as we have a fallback > */ > if (size > PAGE_SIZE) { > -- 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