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Date: Thu, 26 Feb 2015 01:47:06 +0900 (KST) From: SeongJae Park <sj38.park@...il.com> To: Michal Hocko <mhocko@...e.cz> cc: SeongJae Park <sj38.park@...il.com>, akpm@...ux-foundation.org, lauraa@...eaurora.org, minchan@...nel.org, sergey.senozhatsky@...il.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [RFC v2 0/5] introduce gcma 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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