From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752010AbdETArB (ORCPT ); Fri, 19 May 2017 20:47:01 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:8991 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbdETArA (ORCPT ); Fri, 19 May 2017 20:47:00 -0400 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 19 May 2017 17:46:59 -0700 Subject: Re: [PATCH] mm: clarify why we want kmalloc before falling backto vmallock To: Michal Hocko , Andrew Morton CC: Chris Wilson , Vlastimil Babka , , LKML , Michal Hocko References: <20170517080932.21423-1-mhocko@kernel.org> X-Nvconfidentiality: public From: John Hubbard Message-ID: Date: Fri, 19 May 2017 17:46:58 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <20170517080932.21423-1-mhocko@kernel.org> X-Originating-IP: [172.17.160.221] X-ClientProxiedBy: HQMAIL106.nvidia.com (172.18.146.12) To HQMAIL108.nvidia.com (172.18.146.13) Content-Type: text/plain; charset="utf-8"; format=flowed 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 On 05/17/2017 01:09 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 > --- > 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 > */ Thanks for adding this, it's great to have. Here's a slightly polished version of your words, if you like: /* * We want to attempt a large physically contiguous block first because * it is less likely to fragment multiple larger blocks. This approach * therefore contributes less to long term fragmentation than a vmalloc * fallback would. However, make sure that larger requests are not too * disruptive: no OOM killer and no allocation failure warnings, as we * have a fallback. */ thanks, john h > if (size > PAGE_SIZE) { > -- > 2.11.0 > > -- > 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 >