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Date: Wed, 17 Aug 2011 10:06:52 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Mel Gorman <mgorman@...e.de> Cc: Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, XFS <xfs@....sgi.com>, Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@...radead.org>, Johannes Weiner <jweiner@...hat.com>, Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>, Rik van Riel <riel@...hat.com>, Minchan Kim <minchan.kim@...il.com> Subject: Re: [PATCH 5/7] mm: vmscan: Do not writeback filesystem pages in kswapd except in high priority On Thu, 11 Aug 2011 21:25:04 +0100 Mel Gorman <mgorman@...e.de> wrote: > On Thu, Aug 11, 2011 at 06:10:29PM +0900, KAMEZAWA Hiroyuki wrote: > > On Wed, 10 Aug 2011 11:47:18 +0100 > > Mel Gorman <mgorman@...e.de> wrote: > > > > > It is preferable that no dirty pages are dispatched for cleaning from > > > the page reclaim path. At normal priorities, this patch prevents kswapd > > > writing pages. > > > > > > However, page reclaim does have a requirement that pages be freed > > > in a particular zone. If it is failing to make sufficient progress > > > (reclaiming < SWAP_CLUSTER_MAX at any priority priority), the priority > > > is raised to scan more pages. A priority of DEF_PRIORITY - 3 is > > > considered to be the point where kswapd is getting into trouble > > > reclaiming pages. If this priority is reached, kswapd will dispatch > > > pages for writing. > > > > > > Signed-off-by: Mel Gorman <mgorman@...e.de> > > > Reviewed-by: Minchan Kim <minchan.kim@...il.com> > > > > > > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> > > > > Thanks > > > BTW, I'd like to see summary of the effect of priority.. > > > > What sort of summary are you looking for? If pressure is high enough, > writes start happening from reclaim. On NUMA, it can be particularly > pronounced. Here is a summary of page writes from reclaim over a range > of tests > > 512M1P-xfs Page writes file fsmark 8113 74 > 512M1P-xfs Page writes file simple-wb 19895 1 > 512M1P-xfs Page writes file mmap-strm 997 95 > 512M-xfs Page writes file fsmark 12071 9 > 512M-xfs Page writes file simple-wb 31709 1 > 512M-xfs Page writes file mmap-strm 148274 2448 > 512M-4X-xfs Page writes file fsmark 12828 0 > 512M-4X-xfs Page writes file simple-wb 32168 5 > 512M-4X-xfs Page writes file mmap-strm 346460 4405 > 512M-16X-xfs Page writes file fsmark 11566 29 > 512M-16X-xfs Page writes file simple-wb 31935 4 > 512M-16X-xfs Page writes file mmap-strm 38085 4371 > > With 1 processor (512M1P), very few writes occur as for the most part > flushers are keeping up. With 4x times more processors than there are > CPUs (512M-4X), there are more writes by kswapd.. > > 1024M1P-xfs Page writes file fsmark 3446 1 > 1024M1P-xfs Page writes file simple-wb 11697 6 > 1024M1P-xfs Page writes file mmap-strm 4077 446 > 1024M-xfs Page writes file fsmark 5159 0 > 1024M-xfs Page writes file simple-wb 12785 5 > 1024M-xfs Page writes file mmap-strm 251153 8108 > 1024M-4X-xfs Page writes file fsmark 4781 0 > 1024M-4X-xfs Page writes file simple-wb 12486 6 > 1024M-4X-xfs Page writes file mmap-strm 1627122 15000 > 1024M-16X-xfs Page writes file fsmark 3777 1 > 1024M-16X-xfs Page writes file simple-wb 11856 2 > 1024M-16X-xfs Page writes file mmap-strm 6563 2638 > 4608M1P-xfs Page writes file fsmark 1497 0 > 4608M1P-xfs Page writes file simple-wb 4305 0 > 4608M1P-xfs Page writes file mmap-strm 17586 10153 > 4608M-xfs Page writes file fsmark 3380 0 > 4608M-xfs Page writes file simple-wb 5528 0 > 4608M-4X-xfs Page writes file fsmark 4650 0 > 4608M-4X-xfs Page writes file simple-wb 5621 0 > 4608M-4X-xfs Page writes file mmap-strm 149751 18395 > 4608M-16X-xfs Page writes file fsmark 388 0 > 4608M-16X-xfs Page writes file simple-wb 5466 0 > 4608M-16X-xfs Page writes file mmap-strm 3349772 19307 > > This is the same type of tests just with more memory. If enough > processes are running, kswapd will start writing pages as it tries > to reclaim memory. > > 4096M8N-xfs Page writes file fsmark 11571 8163 > 4096M8N-xfs Page writes file simple-wb 28979 11460 > 4096M8N-xfs Page writes file mmap-strm 178999 12181 > 4096M8N-4X-xfs Page writes file fsmark 14421 7487 > 4096M8N-4X-xfs Page writes file simple-wb 26474 10529 > 4096M8N-4X-xfs Page writes file mmap-strm 163770 58765 > 4096M8N-16X-xfs Page writes file fsmark 16726 9265 > 4096M8N-16X-xfs Page writes file simple-wb 28800 11129 > 4096M8N-16X-xfs Page writes file mmap-strm 73303 48267 > > This is with 8 NUMA nodes, each 512M in size. As the flusher threads are > not targetting a specific ndoe, kswapd writing pages happens more > frequently. > Thank you for illustration. > Is this what you are looking for? > I just wondered how 'priority' is used over vmscan.c It's used for - calculate # of pages to be scanned. - sleep(congestion_wait()) - change reclaim mode - reclaim stall detection - quit scan loop - all_unreclaimable detection - swap token - write back skip <----- New! To me, it seems a value is used for many purpose. And I wonder whether this is good or not.. Thanks, -Kame -- 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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