From mboxrd@z Thu Jan 1 00:00:00 1970 From: Suleiman Souhlal Subject: Re: [PATCH 1/4] vmscan: delegate pageout io to flusher thread if current is kswapd Date: Thu, 15 Apr 2010 16:41:44 -0700 Message-ID: References: <20100415013436.GO2493@dastard> <20100415130212.D16E.A69D9226@jp.fujitsu.com> <20100415131106.D174.A69D9226@jp.fujitsu.com> <64BE60A8-EEF9-4AC6-AF0A-0ED3CB544726@freebsd.org> <20100415093214.GV2493@dastard> <85DB7083-8E78-4884-9E76-5BD803C530EF@freebsd.org> <20100415233339.GW2493@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Suleiman Souhlal , KOSAKI Motohiro , Mel Gorman , Chris Mason , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org To: Dave Chinner Return-path: In-Reply-To: <20100415233339.GW2493@dastard> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Apr 15, 2010 at 4:33 PM, Dave Chinner wrote: > On Thu, Apr 15, 2010 at 10:27:09AM -0700, Suleiman Souhlal wrote: >> >> On Apr 15, 2010, at 2:32 AM, Dave Chinner wrote: >> >> >On Thu, Apr 15, 2010 at 01:05:57AM -0700, Suleiman Souhlal wrote: >> >> >> >>On Apr 14, 2010, at 9:11 PM, KOSAKI Motohiro wrote: >> >> >> >>>Now, vmscan pageout() is one of IO throuput degression source. >> >>>Some IO workload makes very much order-0 allocation and reclaim >> >>>and pageout's 4K IOs are making annoying lots seeks. >> >>> >> >>>At least, kswapd can avoid such pageout() because kswapd don't >> >>>need to consider OOM-Killer situation. that's no risk. >> >>> >> >>>Signed-off-by: KOSAKI Motohiro >> >> >> >>What's your opinion on trying to cluster the writes done by pageout, >> >>instead of not doing any paging out in kswapd? >> > >> >XFS already does this in ->writepage to try to minimise the impact >> >of the way pageout issues IO. It helps, but it is still not as good >> >as having all the writeback come from the flusher threads because >> >it's still pretty much random IO. >> >> Doesn't the randomness become irrelevant if you can cluster enough >> pages? > > No. If you are doing full disk seeks between random chunks, then you > still lose a large amount of throughput. e.g. if the seek time is > 10ms and your IO time is 10ms for each 4k page, then increasing the > size ito 64k makes it 10ms seek and 12ms for the IO. We might increase > throughput but we are still limited to 100 IOs per second. We've > gone from 400kB/s to 6MB/s, but that's still an order of magnitude > short of the 100MB/s full size IOs with little in way of seeks > between them will acheive on the same spindle... What I meant was that, theoretically speaking, you could increase the maximum amount of pages that get clustered so that you could get 100MB/s, although it most likely wouldn't be a good idea with the current patch. -- Suleiman -- 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