Re: [lkp-robot] [mm, vmscan] 5e56dfbd83: fsmark.files_per_sec -11.1% regression

Michal Hocko
2017-02-07T14:43:21Z

On Tue 07-02-17 10:22:13, Ye Xiaolong wrote:
> On 02/06, Michal Hocko wrote:
> >On Sat 04-02-17 16:16:04, Ye Xiaolong wrote:
> >> On 01/26, Michal Hocko wrote:
> >> >On Wed 25-01-17 12:27:06, Ye Xiaolong wrote:
> >> >> On 01/24, Michal Hocko wrote:
> >[...]
> >> >> >perf profiles before and after the patch.
> >> >>
> >> >> Here is the perf profiles,
> >> >
> >> >I do not see any reclaim path in the profile... Could you take a
> >> >snapshot of /proc/vmstat and /proc/zoneinfo before and after the test
> >> >please?
> >>
> >> Sorry for the late, just come back from a vacation. Proc data is attached.
> >
> >Sorry, I wasn't clear enough. Could you provide this data for both with
> >the patch applied and without, please?
>
> Ok, please ignore previous attached proc data, you can refer to attached data-5e56d
> and data-69ec9 (without your patch).

Thanks!

base patched [diff]
allocstall_dma32 0 0
allocstall_normal 0 0
pgalloc_dma32 738043 715892
pgalloc_normal 35069802 -895825
pgscan_direct 0 0
pgscan_kswapd 6306707 12099089
pgskip_dma32 0 0
pgskip_normal 0 0
pgsteal_direct 0 0
pgsteal_kswapd 6137737 12099184

So there is no direct reclaim during the test. But there are notably
more allocations from DMA32 zone. kswapd also scans and reclaims much
more pages. We do not have per-zone counters for the reclaim so we
cannot see whether kswapd scanned DMA32 zone more. We, however, can
assume that there were unlikely GFP_DMA32 requests because we would skip
at least some pages on the LRU which we haven't.

kswapd_inodesteal 12173337 -12173337
slabs_scanned 156054 -83094

this is more interesting. It means that the the base kernel has
reclaimed a lot of inodes while the patched not a single one. This is
highly suspicious. This is a NUMA machine with 2 nodes
numa_foreign 8364077 -2819758
numa_hit 27175296 2608395
numa_local 27175860 2607766
numa_miss 8364077 -2819758
numa_other 8363513 -2819129

which suggests that the NUMA locality was much better with the patched
kernel. The broken out numbres from zoneinfo just for reference because
I do not see anything obvious from that. Well, except that the workload
was running on both nodes and the locality was better with the patched
kernel.

numa_foreign_DMA_0 0 0
numa_foreign_DMA32_0 0 0
numa_foreign_Normal_0 7177278 -2467322
numa_foreign_Normal_1 1186799 -352423

numa_hit_DMA32_0 731406 395905
numa_hit_Normal_0 14751993 565687
numa_hit_Normal_1 11692056 1646863

numa_local_DMA_0 0 0
numa_local_DMA32_0 731406 395905
numa_local_Normal_0 14751970 565677
numa_local_Normal_1 11692643 1646244

numa_miss_DMA_0 0 0
numa_miss_DMA32_0 239 321811
numa_miss_Normal_0 1186560 -674234
numa_miss_Normal_1 7177278 -2467322

numa_other_DMA_0 0 0
numa_other_DMA32_0 239 321811
numa_other_Normal_0 1186583 -674224
numa_other_Normal_1 7176691 -2466703

Could you retest with a single NUMA node? I am not familiar with the
benchmark enough to judge it was set up properly for a NUMA machine.
--
Michal Hocko
SUSE Labs