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Date: Wed, 04 Nov 2015 15:47:03 +0800
From: "Huang\, Ying" <ying.huang@...ux.intel.com>
To: Hugh Dickins <hughd@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Josef Bacik <jbacik@...com>, Yu Zhao <yuzhao@...gle.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] tmpfs: avoid a little creat and stat slowdown
Hugh Dickins <hughd@...gle.com> writes:
> LKP reports that v4.2 commit afa2db2fb6f1 ("tmpfs: truncate prealloc
> blocks past i_size") causes a 14.5% slowdown in the AIM9 creat-clo
> benchmark.
>
> creat-clo does just what you'd expect from the name, and creat's O_TRUNC
> on 0-length file does indeed get into more overhead now shmem_setattr()
> tests "0 <= 0" instead of "0 < 0".
>
> I'm not sure how much we care, but I think it would not be too VW-like
> to add in a check for whether any pages (or swap) are allocated: if none
> are allocated, there's none to remove from the radix_tree. At first I
> thought that check would be good enough for the unmaps too, but no: we
> should not skip the unlikely case of unmapping pages beyond the new EOF,
> which were COWed from holes which have now been reclaimed, leaving none.
>
> This gives me an 8.5% speedup: on Haswell instead of LKP's Westmere,
> and running a debug config before and after: I hope those account for
> the lesser speedup.
>
> And probably someone has a benchmark where a thousand threads keep on
> stat'ing the same file repeatedly: forestall that report by adjusting
> v4.3 commit 44a30220bc0a ("shmem: recalculate file inode when fstat")
> not to take the spinlock in shmem_getattr() when there's no work to do.
>
> Reported-by: Ying Huang <ying.huang@...ux.intel.com>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
Hi, Hugh,
Thanks a lot for your support! The test on LKP shows that this patch
restores a big part of the regression! In following list,
c435a390574d012f8d30074135d8fcc6f480b484: is parent commit
afa2db2fb6f15f860069de94a1257db57589fe95: is the first bad commit has
performance regression.
43819159da2b77fedcf7562134d6003dccd6a068: is the fixing patch
=========================================================================================
compiler/cpufreq_governor/kconfig/rootfs/tbox_group/test/testcase/testtime:
gcc-4.9/performance/x86_64-rhel/debian-x86_64-2015-02-07.cgz/lkp-wsx02/creat-clo/aim9/300s
commit:
c435a390574d012f8d30074135d8fcc6f480b484
afa2db2fb6f15f860069de94a1257db57589fe95
43819159da2b77fedcf7562134d6003dccd6a068
c435a390574d012f afa2db2fb6f15f860069de94a1 43819159da2b77fedcf7562134
---------------- -------------------------- --------------------------
%stddev %change %stddev %change %stddev
\ | \ | \
563556 ± 1% -12.5% 493033 ± 5% -5.6% 531968 ± 1% aim9.creat-clo.ops_per_sec
11836 ± 7% +11.4% 13184 ± 7% +15.0% 13608 ± 5% numa-meminfo.node1.SReclaimable
10121526 ± 3% -12.1% 8897097 ± 5% -4.1% 9707953 ± 4% proc-vmstat.pgalloc_normal
9.34 ± 4% -11.4% 8.28 ± 3% -4.8% 8.88 ± 2% time.user_time
3480 ± 3% -2.5% 3395 ± 1% -28.5% 2488 ± 3% vmstat.system.cs
203275 ± 17% -6.8% 189453 ± 5% -34.4% 133352 ± 11% cpuidle.C1-NHM.usage
8081280 ±129% -93.3% 538377 ± 97% +31.5% 10625496 ±106% cpuidle.C1E-NHM.time
3144 ± 58% +619.0% 22606 ± 56% +903.9% 31563 ± 0% numa-vmstat.node0.numa_other
2958 ± 7% +11.4% 3295 ± 7% +15.0% 3401 ± 5% numa-vmstat.node1.nr_slab_reclaimable
45074 ± 5% -43.4% 25494 ± 57% -68.7% 14105 ± 2% numa-vmstat.node2.numa_other
56140 ± 0% +0.0% 56158 ± 0% -94.4% 3120 ± 0% slabinfo.Acpi-ParseExt.active_objs
1002 ± 0% +0.0% 1002 ± 0% -92.0% 80.00 ± 0% slabinfo.Acpi-ParseExt.active_slabs
56140 ± 0% +0.0% 56158 ± 0% -94.4% 3120 ± 0% slabinfo.Acpi-ParseExt.num_objs
1002 ± 0% +0.0% 1002 ± 0% -92.0% 80.00 ± 0% slabinfo.Acpi-ParseExt.num_slabs
1079 ± 5% -10.8% 962.00 ± 10% -100.0% 0.00 ± -1% slabinfo.blkdev_ioc.active_objs
1079 ± 5% -10.8% 962.00 ± 10% -100.0% 0.00 ± -1% slabinfo.blkdev_ioc.num_objs
110.67 ± 39% +74.4% 193.00 ± 46% +317.5% 462.00 ± 8% slabinfo.blkdev_queue.active_objs
189.33 ± 23% +43.7% 272.00 ± 33% +151.4% 476.00 ± 10% slabinfo.blkdev_queue.num_objs
1129 ± 10% -1.9% 1107 ± 7% +20.8% 1364 ± 6% slabinfo.blkdev_requests.active_objs
1129 ± 10% -1.9% 1107 ± 7% +20.8% 1364 ± 6% slabinfo.blkdev_requests.num_objs
1058 ± 3% -10.3% 949.00 ± 9% -100.0% 0.00 ± -1% slabinfo.file_lock_ctx.active_objs
1058 ± 3% -10.3% 949.00 ± 9% -100.0% 0.00 ± -1% slabinfo.file_lock_ctx.num_objs
4060 ± 1% -2.1% 3973 ± 1% -10.5% 3632 ± 1% slabinfo.files_cache.active_objs
4060 ± 1% -2.1% 3973 ± 1% -10.5% 3632 ± 1% slabinfo.files_cache.num_objs
10001 ± 0% -0.3% 9973 ± 0% -61.1% 3888 ± 0% slabinfo.ftrace_event_field.active_objs
10001 ± 0% -0.3% 9973 ± 0% -61.1% 3888 ± 0% slabinfo.ftrace_event_field.num_objs
1832 ± 0% +0.4% 1840 ± 0% -100.0% 0.00 ± -1% slabinfo.ftrace_event_file.active_objs
1832 ± 0% +0.4% 1840 ± 0% -100.0% 0.00 ± -1% slabinfo.ftrace_event_file.num_objs
1491 ± 5% -2.3% 1456 ± 6% +12.0% 1669 ± 4% slabinfo.mnt_cache.active_objs
1491 ± 5% -2.3% 1456 ± 6% +12.0% 1669 ± 4% slabinfo.mnt_cache.num_objs
126.33 ± 19% +10.2% 139.17 ± 9% -100.0% 0.00 ± -1% slabinfo.nfs_commit_data.active_objs
126.33 ± 19% +10.2% 139.17 ± 9% -100.0% 0.00 ± -1% slabinfo.nfs_commit_data.num_objs
97.17 ± 20% -9.1% 88.33 ± 28% -100.0% 0.00 ± -1% slabinfo.user_namespace.active_objs
97.17 ± 20% -9.1% 88.33 ± 28% -100.0% 0.00 ± -1% slabinfo.user_namespace.num_objs
Best Regards,
Huang, Ying
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