From: Joonsoo Kim Subject: Re: [PATCHv4 0/3] new APIs to allocate buffer-cache with user specific flag Date: Mon, 15 Sep 2014 10:10:18 +0900 Message-ID: <20140915011018.GA2676@js1304-P5Q-DELUXE> References: <1409815781-28011-1-git-send-email-gioh.kim@lge.com> <20140904151612.7bf5b813069ff78973e01571@linux-foundation.org> <540905B1.1050200@lge.com> <20140905011419.GE4364@thunk.org> <20140905014808.GA26070@js1304-P5Q-DELUXE> <20140905031735.GD1971@thunk.org> <20140905073247.GA31827@js1304-P5Q-DELUXE> <20140905141416.GA1510@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mel Gorman , Marek Szyprowski , Michal Nazarewicz To: Theodore Ts'o , Gioh Kim , Andrew Morton , jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, paulmck@linux.vnet.ibm.com, peterz@infradead.org, adilger.kernel@dilger.ca, minchan@kernel.org, gunho.lee@lge.com Return-path: Content-Disposition: inline In-Reply-To: <20140905141416.GA1510@thunk.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Fri, Sep 05, 2014 at 10:14:16AM -0400, Theodore Ts'o wrote: > On Fri, Sep 05, 2014 at 04:32:48PM +0900, Joonsoo Kim wrote: > > I also test another approach, such as allocate freepage in CMA > > reserved region as late as possible, which is also similar to your > > suggestion and this doesn't works well. When reclaim is started, > > too many pages reclaim at once, because lru list has successive pages > > in CMA region and these doesn't help kswapd's reclaim. kswapd stop > > reclaiming when freepage count is recovered. But, CMA pages isn't > > counted for freepage for kswapd because they can't be usable for > > unmovable, reclaimable allocation. So kswap reclaim too many pages > > at once unnecessarilly. > > Have you considered putting the pages in a CMA region in a separate > zone? After all, that's what we originally did with brain-damaged > hardware that could only DMA into the low 16M of memory. We just > reserved a separate zone for that? That way, we could do > zone-directed reclaim and free pages in that zone, if that was what > was actually needed. Sorry for long delay. It was long holidays. No, I haven't consider it. It sounds good idea to place the pages in a CMA region into a separate zone. Perhaps we can remove one of migratetype, MIGRATE_CMA, with this way and it would be a good long-term architecture for CMA. I don't know exact history and reason why CMA is implemented in current form. Ccing some experts in this area. Thanks.