From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id E40CF6B0253 for ; Mon, 2 May 2016 03:49:52 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id w143so69838556wmw.3 for ; Mon, 02 May 2016 00:49:52 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id g78si19428550wmc.117.2016.05.02.00.49.51 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 02 May 2016 00:49:51 -0700 (PDT) Subject: Re: [PATCH v2 0/6] Introduce ZONE_CMA References: <1461561670-28012-1-git-send-email-iamjoonsoo.kim@lge.com> <20160425053653.GA25662@js1304-P5Q-DELUXE> <20160428103927.GM2858@techsingularity.net> <20160429065145.GA19896@js1304-P5Q-DELUXE> <20160429092902.GQ2858@techsingularity.net> <20160502061423.GA31646@js1304-P5Q-DELUXE> From: Vlastimil Babka Message-ID: <5727069B.5070600@suse.cz> Date: Mon, 2 May 2016 09:49:47 +0200 MIME-Version: 1.0 In-Reply-To: <20160502061423.GA31646@js1304-P5Q-DELUXE> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim , Mel Gorman Cc: Andrew Morton , Rik van Riel , Johannes Weiner , Laura Abbott , Minchan Kim , Marek Szyprowski , Michal Nazarewicz , "Aneesh Kumar K.V" , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 05/02/2016 08:14 AM, Joonsoo Kim wrote: >>> > >Although it's separate issue, I should mentioned one thing. Related to >>> > >I/O pinning issue, ZONE_CMA don't get blockdev allocation request so >>> > >I/O pinning problem is much reduced. >>> > > >> > >> >This is not super-clear from the patch. blockdev is using GFP_USER so it >> >already should not be classed as MOVABLE. I could easily be looking in >> >the wrong place or missed which allocation path sets GFP_MOVABLE. > Okay. Please see sb_bread(), sb_getblk(), __getblk() and __bread() in > include/linux/buffer_head.h. These are main functions used by blockdev > and they uses GFP_MOVABLE. To fix permanent allocation case which is > used by mount and cannot be released until umount, Gioh introduces > sb_bread_unmovable() but there are many remaining issues that prevent > migration at the moment and avoid blockdev allocation from CMA area is > preferable approach. Hm Patch 3/6 describes the lack of blockdev allocations mostly as a limitation, although it does mention the possible advantages later. Anyway, this doesn't have to be specific to ZONE_CMA, right? You could just change ALLOC_CMA handling to consider GFP_HIGHUSER_MOVABLE instead of just __GFP_MOVABLE. For ZONE_CMA it might be inevitable as you describe, but it's already possible to do that now, if the advantages are larger than the disadvantages. -- 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