From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id C4A43280753 for ; Fri, 19 May 2017 20:47:00 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id a66so67868895pfl.6 for ; Fri, 19 May 2017 17:47:00 -0700 (PDT) Received: from hqemgate16.nvidia.com (hqemgate16.nvidia.com. [216.228.121.65]) by mx.google.com with ESMTPS id v14si9806620plk.134.2017.05.19.17.46.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 May 2017 17:46:59 -0700 (PDT) Subject: Re: [PATCH] mm: clarify why we want kmalloc before falling backto vmallock References: <20170517080932.21423-1-mhocko@kernel.org> From: John Hubbard Message-ID: Date: Fri, 19 May 2017 17:46:58 -0700 MIME-Version: 1.0 In-Reply-To: <20170517080932.21423-1-mhocko@kernel.org> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Andrew Morton Cc: Chris Wilson , Vlastimil Babka , linux-mm@kvack.org, LKML , Michal Hocko 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 > -- 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