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Date: Wed, 14 Sep 2011 23:33:34 -0400 From: Satoru Moriya <satoru.moriya@....com> To: Andrew Morton <akpm@...ux-foundation.org>, Rik van Riel <riel@...hat.com> CC: Randy Dunlap <rdunlap@...otime.net>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "lwoodman@...hat.com" <lwoodman@...hat.com>, Seiji Aguchi <saguchi@...hat.com>, "hughd@...gle.com" <hughd@...gle.com>, "hannes@...xchg.org" <hannes@...xchg.org> Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable On 09/02/2011 12:31 PM, Satoru Moriya wrote: > On 09/01/2011 05:58 PM, Andrew Morton wrote: >> On Thu, 1 Sep 2011 15:26:50 -0400 >> Rik van Riel <riel@...hat.com> wrote: > Anyway, now I'm testing this patch and will report a test result later. Sorry for late reply. Here is my test result. I ran some sample workloads and measure memory allocation latency (latency of __alloc_page_nodemask()). The test is like following: - CPU: 1 socket, 4 core - Memory: 4GB - Background load: $ dd if=/dev/zero of=/tmp/tmp1 $ dd if=/dev/zero of=/tmp/tmp2 $ dd if=/dev/zero of=/tmp/tmp3 - Main load: $ mapped-file-stream 1 $((1024 * 1024 * 640)) --(*) (*) This is made by Johannes Weiner https://lkml.org/lkml/2010/8/30/226 It allocates/access 640MByte memory at a burst. The result is follwoing: | | extra | | default | kbytes | -------------------------------------------------------------- min_free_kbytes | 8113 | 8113 | extra_free_kbytes | 0 | 640*1024 | (KB) -------------------------------------------------------------- worst latency | 517.762 | 20.775 | (usec) -------------------------------------------------------------- vmstat result | | | nr_vmscan_write | 0 | 0 | pgsteal_dma | 0 | 0 | pgsteal_dma32 | 143667 | 144882 | pgsteal_normal | 31486 | 27001 | pgsteal_movable | 0 | 0 | pgscan_kswapd_dma | 0 | 0 | pgscan_kswapd_dma32 | 138617 | 156351 | pgscan_kswapd_normal | 30593 | 27955 | pgscan_kswapd_movable | 0 | 0 | pgscan_direct_dma | 0 | 0 | pgscan_direct_dma32 | 5050 | 0 | pgscan_direct_normal | 896 | 0 | pgscan_direct_movable | 0 | 0 | kswapd_steal | 169207 | 171883 | kswapd_inodesteal | 0 | 0 | kswapd_low_wmark_hit_quickly | 43 | 45 | kswapd_high_wmark_hit_quickly | 1 | 0 | allocstall | 32 | 0 | As you can see, in the default case there were 32 direct reclaim (allocstall) and its worst latency was 517.762 usecs. This value may be larger if a process would sleep or issue I/O in the direct reclaim path. OTOH, ii the other case where I add extra free bytes, there were no direct reclaim and its worst latency was 20.775 usecs. In this test case, we can avoid direct reclaim and keep a latency low. Tested-by: Satoru Moriya <satoru.moriya@....com> -- 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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