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@xxxxxxx> 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@xxxxxxx> > > Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > > > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > 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. Is this what you are looking for? -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>