From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754375AbdETH1o (ORCPT ); Sat, 20 May 2017 03:27:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:55635 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753827AbdETH1l (ORCPT ); Sat, 20 May 2017 03:27:41 -0400 Date: Sat, 20 May 2017 09:27:37 +0200 From: Michal Hocko To: John Hubbard Cc: Andrew Morton , Chris Wilson , Vlastimil Babka , linux-mm@kvack.org, LKML Subject: Re: [PATCH] mm: clarify why we want kmalloc before falling backto vmallock Message-ID: <20170520072737.GB11925@dhcp22.suse.cz> References: <20170517080932.21423-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 19-05-17 17:46:58, John Hubbard wrote: > 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. > */ Looks ok to me. -- Michal Hocko SUSE Labs