From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f43.google.com (mail-pa0-f43.google.com [209.85.220.43]) by kanga.kvack.org (Postfix) with ESMTP id 7D3E16B0032 for ; Wed, 25 Feb 2015 11:44:25 -0500 (EST) Received: by pabkx10 with SMTP id kx10so6537249pab.0 for ; Wed, 25 Feb 2015 08:44:25 -0800 (PST) Received: from mail-pd0-x234.google.com (mail-pd0-x234.google.com. [2607:f8b0:400e:c02::234]) by mx.google.com with ESMTPS id bn1si6627404pbb.257.2015.02.25.08.44.23 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Feb 2015 08:44:23 -0800 (PST) Received: by pdev10 with SMTP id v10so5983203pde.10 for ; Wed, 25 Feb 2015 08:44:23 -0800 (PST) From: SeongJae Park Date: Thu, 26 Feb 2015 01:47:06 +0900 (KST) Subject: Re: [RFC v2 0/5] introduce gcma In-Reply-To: <20150225161158.GI26680@dhcp22.suse.cz> Message-ID: References: <1424721263-25314-1-git-send-email-sj38.park@gmail.com> <20150224144804.GE15626@dhcp22.suse.cz> <20150225161158.GI26680@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: SeongJae Park , akpm@linux-foundation.org, lauraa@codeaurora.org, minchan@kernel.org, sergey.senozhatsky@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, 25 Feb 2015, Michal Hocko wrote: > On Wed 25-02-15 14:31:08, SeongJae Park wrote: >> Hello Michal, >> >> Thanks for your comment :) >> >> On Tue, 24 Feb 2015, Michal Hocko wrote: >> >>> On Tue 24-02-15 04:54:18, SeongJae Park wrote: >>> [...] >>>> include/linux/cma.h | 4 + >>>> include/linux/gcma.h | 64 +++ >>>> mm/Kconfig | 24 + >>>> mm/Makefile | 1 + >>>> mm/cma.c | 113 ++++- >>>> mm/gcma.c | 1321 ++++++++++++++++++++++++++++++++++++++++++++++++++ >>>> 6 files changed, 1508 insertions(+), 19 deletions(-) >>>> create mode 100644 include/linux/gcma.h >>>> create mode 100644 mm/gcma.c >>> >>> Wow this is huge! And I do not see reason for it to be so big. Why >>> cannot you simply define (per-cma area) 2-class users policy? Either via >>> kernel command line or export areas to userspace and allow to set policy >>> there. >> >> For implementation of the idea, we should develop not only policy selection, >> but also backend for discardable memory. Most part of this patch were made >> for the backend. > > What is the backend and why is it needed? I thought the discardable will > go back to the CMA pool. I mean the cover email explained why the > current CMA allocation policy might lead to lower success rate or > stalls. So I would expect a new policy would be a relatively small > change in the CMA allocation path to serve 2-class users as per policy. > It is not clear to my why we need to pull a whole gcma layer in. I might > be missing something obvious because I haven't looked at the patches yet > but this should better be explained in the cover letter. I meant backend for 2nd-class clients like cleancache and frontswap. Because implementing backend for cleancache or frontswap is subsystem's responsibility, gcma was needed to implement those backend. I believe second ("gcma: utilize reserved memory as discardable memory") and third ("gcma: adopt cleancache and frontswap as second-class clients") could be helpful to understand about that. And yes, I agree the explanation was not enough. My fault, sorry. My explanation was too concentrated on policy itself. I should explained about how the policy could be implemented and how gcma did. I will explain about that in coverletter with next version. Thanks for your helpful and nice comment. Thanks, SeongJae Park > > Thanks! > -- > Michal Hocko > SUSE Labs > -- 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