Messages in this thread | | | From | Satoru Moriya <> | Date | Wed, 14 Sep 2011 23:33:34 -0400 | Subject | Re: [PATCH -v2 -mm] add extra free kbytes tunable |
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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@redhat.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@hds.com>
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