Re: [PATCH 0/8] Reduce latencies and improve overall reclaim efficiencyv2
From: Christian Ehrhardt
Date: Thu Oct 14 2010 - 11:28:49 EST
Seing the patches Mel sent a few weeks ago I realized that this series might be at least partially related to my reports in 1Q 2010 - so I ran my testcase on a few kernels to provide you with some more backing data.
Results are always the average of three iozone runs as it is known to be somewhat noisy - especially when affected by the issue I try to show here.
As discussed in detail in older threads the setup uses 16 disks and scales the number of concurrent iozone processes.
Processes are evenly distributed so that it always is one process per disk.
In the past we reported 40% to 80% degradation for the sequential read case based on 2.6.32 which can still be seen.
What we found was that the allocations for page cache with GFP_COLD flag loop a long time between try_to_free, get_page, reclaim as free makes some progress and due to that GFP_COLD allocations can loop and retry.
In addition my case had no writes at all, which forced congestion_wait to wait the full timeout all the time.
Kernel (git) 4 8 16 deviation #16 case comment
linux-2.6.30 902694 1396073 1892624 base base
linux-2.6.32 752008 990425 932938 -50.7% impact as reported in 1Q 2010
linux-2.6.35 63532 71573 64083 -96.6% got even worse
linux-2.6.35.6 176485 174442 212102 -88.8% fixes useful, but still far away
linux-2.6.36-rc4-trace 119683 188997 187012 -90.1% still bad
linux-2.6.36-rc4-fix 884431 1114073 1470659 -22.3% Mels fixes help a lot!
So much from the case that I used when I reported the issue earlier this year.
The short summary is that the patch series from Mel helps a lot for my test case.
So I guess Mel you now want some traces of the last two cases right?
Could you give me some minimal advice what/how you would exactly need.
In addition it worked really fine, so you can add both, however you like.
Reported-by: <ehrhardt@xxxxxxxxxxxxxxxxxx>
Tested-by: <ehrhardt@xxxxxxxxxxxxxxxxxx>
Note: it might be worth to mention that the write case improved a lot since 2.6.30.
Not directly related to the read degradations, but with up to 150% (write) 272% (rewrite).
Therefore not everything is bad :-)
Any further comments or questions?
Christian
On 09/15/2010 02:27 PM, Mel Gorman wrote:
> This is v2 of a series to reduce some of the latencies seen in page reclaim
> and to improve the efficiency a bit. There are a number of changes in this
> revision. The first is to drop the patches avoiding writeback from direct
> reclaim again. Wu asked me to look at a large number of his patches and I felt
> it was best to do that independent of this series which should be relatively
> uncontroversial. The second big change is to wait_iff_congested(). There
> were a few complaints that the avoidance heuristic was way too fuzzy and
> so I tried following Andrew's suggestion to take note of the return value
> of bdi_write_congested() in may_write_to_queue() to identify when a zone
> is congested.
>
> Changelog since V2
> o Reshuffle patches to order from least to most controversial
> o Drop the patches dealing with writeback avoidance. Wu is working
> on some patches that potentially collide with this area so it
> will be revisited later
> o Use BDI congestion feedback in wait_iff_congested() instead of
> making a determination based on number of pages currently being
> written back
> o Do not use lock_page in pageout path
> o Rebase to 2.6.36-rc4
>
> Changelog since V1
> o Fix mis-named function in documentation
> o Added reviewed and acked bys
>
> There have been numerous reports of stalls that pointed at the problem being
> somewhere in the VM. There are multiple roots to the problems which means
> dealing with any of the root problems in isolation is tricky to justify on
> their own and they would still need integration testing. This patch series
> puts together two different patch sets which in combination should tackle
> some of the root causes of latency problems being reported.
>
> Patch 1 adds a tracepoint for shrink_inactive_list. For this series, the
> most important results is being able to calculate the scanning/reclaim
> ratio as a measure of the amount of work being done by page reclaim.
>
> Patch 2 accounts for time spent in congestion_wait.
>
> Patches 3-6 were originally developed by Kosaki Motohiro but reworked for
> this series. It has been noted that lumpy reclaim is far too aggressive and
> trashes the system somewhat. As SLUB uses high-order allocations, a large
> cost incurred by lumpy reclaim will be noticeable. It was also reported
> during transparent hugepage support testing that lumpy reclaim was trashing
> the system and these patches should mitigate that problem without disabling
> lumpy reclaim.
>
> Patch 7 adds wait_iff_congested() and replaces some callers of congestion_wait().
> wait_iff_congested() only sleeps if there is a BDI that is currently congested.
>
> Patch 8 notes that any BDI being congested is not necessarily a problem
> because there could be multiple BDIs of varying speeds and numberous zones. It
> attempts to track when a zone being reclaimed contains many pages backed
> by a congested BDI and if so, reclaimers wait on the congestion queue.
>
> I ran a number of tests with monitoring on X86, X86-64 and PPC64. Each
> machine had 3G of RAM and the CPUs were
>
> X86: Intel P4 2-core
> X86-64: AMD Phenom 4-core
> PPC64: PPC970MP
>
> Each used a single disk and the onboard IO controller. Dirty ratio was left
> at 20. I'm just going to report for X86-64 and PPC64 in a vague attempt to
> keep this report short. Four kernels were tested each based on v2.6.36-rc4
>
> traceonly-v2r2: Patches 1 and 2 to instrument vmscan reclaims and congestion_wait
> lowlumpy-v2r3: Patches 1-6 to test if lumpy reclaim is better
> waitcongest-v2r3: Patches 1-7 to only wait on congestion
> waitwriteback-v2r4: Patches 1-8 to detect when a zone is congested
>
> nocongest-v1r5: Patches 1-3 for testing wait_iff_congestion
> nodirect-v1r5: Patches 1-10 to disable filesystem writeback for better IO
>
> The tests run were as follows
>
> kernbench
> compile-based benchmark. Smoke test performance
>
> sysbench
> OLTP read-only benchmark. Will be re-run in the future as read-write
>
> micro-mapped-file-stream
> This is a micro-benchmark from Johannes Weiner that accesses a
> large sparse-file through mmap(). It was configured to run in only
> single-CPU mode but can be indicative of how well page reclaim
> identifies suitable pages.
>
> stress-highalloc
> Tries to allocate huge pages under heavy load.
>
> kernbench, iozone and sysbench did not report any performance regression
> on any machine. sysbench did pressure the system lightly and there was reclaim
> activity but there were no difference of major interest between the kernels.
>
> X86-64 micro-mapped-file-stream
>
> traceonly-v2r2 lowlumpy-v2r3 waitcongest-v2r3 waitwriteback-v2r4
> pgalloc_dma 1639.00 ( 0.00%) 667.00 (-145.73%) 1167.00 ( -40.45%) 578.00 (-183.56%)
> pgalloc_dma32 2842410.00 ( 0.00%) 2842626.00 ( 0.01%) 2843043.00 ( 0.02%) 2843014.00 ( 0.02%)
> pgalloc_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pgsteal_dma 729.00 ( 0.00%) 85.00 (-757.65%) 609.00 ( -19.70%) 125.00 (-483.20%)
> pgsteal_dma32 2338721.00 ( 0.00%) 2447354.00 ( 4.44%) 2429536.00 ( 3.74%) 2436772.00 ( 4.02%)
> pgsteal_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pgscan_kswapd_dma 1469.00 ( 0.00%) 532.00 (-176.13%) 1078.00 ( -36.27%) 220.00 (-567.73%)
> pgscan_kswapd_dma32 4597713.00 ( 0.00%) 4503597.00 ( -2.09%) 4295673.00 ( -7.03%) 3891686.00 ( -18.14%)
> pgscan_kswapd_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pgscan_direct_dma 71.00 ( 0.00%) 134.00 ( 47.01%) 243.00 ( 70.78%) 352.00 ( 79.83%)
> pgscan_direct_dma32 305820.00 ( 0.00%) 280204.00 ( -9.14%) 600518.00 ( 49.07%) 957485.00 ( 68.06%)
> pgscan_direct_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pageoutrun 16296.00 ( 0.00%) 21254.00 ( 23.33%) 18447.00 ( 11.66%) 20067.00 ( 18.79%)
> allocstall 443.00 ( 0.00%) 273.00 ( -62.27%) 513.00 ( 13.65%) 1568.00 ( 71.75%)
>
> These are based on the raw figures taken from /proc/vmstat. It's a rough
> measure of reclaim activity. Note that allocstall counts are higher because
> we are entering direct reclaim more often as a result of not sleeping in
> congestion. In itself, it's not necessarily a bad thing. It's easier to
> get a view of what happened from the vmscan tracepoint report.
>
> FTrace Reclaim Statistics: vmscan
>
> traceonly-v2r2 lowlumpy-v2r3 waitcongest-v2r3 waitwriteback-v2r4
> Direct reclaims 443 273 513 1568
> Direct reclaim pages scanned 305968 280402 600825 957933
> Direct reclaim pages reclaimed 43503 19005 30327 117191
> Direct reclaim write file async I/O 0 0 0 0
> Direct reclaim write anon async I/O 0 3 4 12
> Direct reclaim write file sync I/O 0 0 0 0
> Direct reclaim write anon sync I/O 0 0 0 0
> Wake kswapd requests 187649 132338 191695 267701
> Kswapd wakeups 3 1 4 1
> Kswapd pages scanned 4599269 4454162 4296815 3891906
> Kswapd pages reclaimed 2295947 2428434 2399818 2319706
> Kswapd reclaim write file async I/O 1 0 1 1
> Kswapd reclaim write anon async I/O 59 187 41 222
> Kswapd reclaim write file sync I/O 0 0 0 0
> Kswapd reclaim write anon sync I/O 0 0 0 0
> Time stalled direct reclaim (seconds) 4.34 2.52 6.63 2.96
> Time kswapd awake (seconds) 11.15 10.25 11.01 10.19
>
> Total pages scanned 4905237 4734564 4897640 4849839
> Total pages reclaimed 2339450 2447439 2430145 2436897
> %age total pages scanned/reclaimed 47.69% 51.69% 49.62% 50.25%
> %age total pages scanned/written 0.00% 0.00% 0.00% 0.00%
> %age file pages scanned/written 0.00% 0.00% 0.00% 0.00%
> Percentage Time Spent Direct Reclaim 29.23% 19.02% 38.48% 20.25%
> Percentage Time kswapd Awake 78.58% 78.85% 76.83% 79.86%
>
> What is interesting here for nocongest in particular is that while direct
> reclaim scans more pages, the overall number of pages scanned remains the same
> and the ratio of pages scanned to pages reclaimed is more or less the same. In
> other words, while we are sleeping less, reclaim is not doing more work and
> as direct reclaim and kswapd is awake for less time, it would appear to be doing less work.
>
> FTrace Reclaim Statistics: congestion_wait
> Direct number congest waited 87 196 64 0
> Direct time congest waited 4604ms 4732ms 5420ms 0ms
> Direct full congest waited 72 145 53 0
> Direct number conditional waited 0 0 324 1315
> Direct time conditional waited 0ms 0ms 0ms 0ms
> Direct full conditional waited 0 0 0 0
> KSwapd number congest waited 20 10 15 7
> KSwapd time congest waited 1264ms 536ms 884ms 284ms
> KSwapd full congest waited 10 4 6 2
> KSwapd number conditional waited 0 0 0 0
> KSwapd time conditional waited 0ms 0ms 0ms 0ms
> KSwapd full conditional waited 0 0 0 0
>
> The vanilla kernel spent 8 seconds asleep in direct reclaim and no time at
> all asleep with the patches.
>
> MMTests Statistics: duration
> User/Sys Time Running Test (seconds) 10.51 10.73 10.6 11.66
> Total Elapsed Time (seconds) 14.19 13.00 14.33 12.76
>
> Overall, the tests completed faster. It is interesting to note that backing off further
> when a zone is congested and not just a BDI was more efficient overall.
>
> PPC64 micro-mapped-file-stream
> pgalloc_dma 3024660.00 ( 0.00%) 3027185.00 ( 0.08%) 3025845.00 ( 0.04%) 3026281.00 ( 0.05%)
> pgalloc_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pgsteal_dma 2508073.00 ( 0.00%) 2565351.00 ( 2.23%) 2463577.00 ( -1.81%) 2532263.00 ( 0.96%)
> pgsteal_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pgscan_kswapd_dma 4601307.00 ( 0.00%) 4128076.00 ( -11.46%) 3912317.00 ( -17.61%) 3377165.00 ( -36.25%)
> pgscan_kswapd_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pgscan_direct_dma 629825.00 ( 0.00%) 971622.00 ( 35.18%) 1063938.00 ( 40.80%) 1711935.00 ( 63.21%)
> pgscan_direct_normal 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%) 0.00 ( 0.00%)
> pageoutrun 27776.00 ( 0.00%) 20458.00 ( -35.77%) 18763.00 ( -48.04%) 18157.00 ( -52.98%)
> allocstall 977.00 ( 0.00%) 2751.00 ( 64.49%) 2098.00 ( 53.43%) 5136.00 ( 80.98%)
>
> Similar trends to x86-64. allocstalls are up but it's not necessarily bad.
>
> FTrace Reclaim Statistics: vmscan
> Direct reclaims 977 2709 2098 5136
> Direct reclaim pages scanned 629825 963814 1063938 1711935
> Direct reclaim pages reclaimed 75550 242538 150904 387647
> Direct reclaim write file async I/O 0 0 0 2
> Direct reclaim write anon async I/O 0 10 0 4
> Direct reclaim write file sync I/O 0 0 0 0
> Direct reclaim write anon sync I/O 0 0 0 0
> Wake kswapd requests 392119 1201712 571935 571921
> Kswapd wakeups 3 2 3 3
> Kswapd pages scanned 4601307 4128076 3912317 3377165
> Kswapd pages reclaimed 2432523 2318797 2312673 2144616
> Kswapd reclaim write file async I/O 20 1 1 1
> Kswapd reclaim write anon async I/O 57 132 11 121
> Kswapd reclaim write file sync I/O 0 0 0 0
> Kswapd reclaim write anon sync I/O 0 0 0 0
> Time stalled direct reclaim (seconds) 6.19 7.30 13.04 10.88
> Time kswapd awake (seconds) 21.73 26.51 25.55 23.90
>
> Total pages scanned 5231132 5091890 4976255 5089100
> Total pages reclaimed 2508073 2561335 2463577 2532263
> %age total pages scanned/reclaimed 47.95% 50.30% 49.51% 49.76%
> %age total pages scanned/written 0.00% 0.00% 0.00% 0.00%
> %age file pages scanned/written 0.00% 0.00% 0.00% 0.00%
> Percentage Time Spent Direct Reclaim 18.89% 20.65% 32.65% 27.65%
> Percentage Time kswapd Awake 72.39% 80.68% 78.21% 77.40%
>
> Again, a similar trend that the congestion_wait changes mean that direct
> reclaim scans more pages but the overall number of pages scanned while
> slightly reduced, are very similar. The ratio of scanning/reclaimed remains
> roughly similar. The downside is that kswapd and direct reclaim was awake
> longer and for a larger percentage of the overall workload. It's possible
> there were big differences in the amount of time spent reclaiming slab
> pages between the different kernels which is plausible considering that
> the micro tests runs after fsmark and sysbench.
>
> Trace Reclaim Statistics: congestion_wait
> Direct number congest waited 845 1312 104 0
> Direct time congest waited 19416ms 26560ms 7544ms 0ms
> Direct full congest waited 745 1105 72 0
> Direct number conditional waited 0 0 1322 2935
> Direct time conditional waited 0ms 0ms 12ms 312ms
> Direct full conditional waited 0 0 0 3
> KSwapd number congest waited 39 102 75 63
> KSwapd time congest waited 2484ms 6760ms 5756ms 3716ms
> KSwapd full congest waited 20 48 46 25
> KSwapd number conditional waited 0 0 0 0
> KSwapd time conditional waited 0ms 0ms 0ms 0ms
> KSwapd full conditional waited 0 0 0 0
>
> The vanilla kernel spent 20 seconds asleep in direct reclaim and only 312ms
> asleep with the patches. The time kswapd spent congest waited was also
> reduced by a large factor.
>
> MMTests Statistics: duration
> ser/Sys Time Running Test (seconds) 26.58 28.05 26.9 28.47
> Total Elapsed Time (seconds) 30.02 32.86 32.67 30.88
>
> With all patches applies, the completion times are very similar.
>
>
> X86-64 STRESS-HIGHALLOC
> traceonly-v2r2 lowlumpy-v2r3 waitcongest-v2r3waitwriteback-v2r4
> Pass 1 82.00 ( 0.00%) 84.00 ( 2.00%) 85.00 ( 3.00%) 85.00 ( 3.00%)
> Pass 2 90.00 ( 0.00%) 87.00 (-3.00%) 88.00 (-2.00%) 89.00 (-1.00%)
> At Rest 92.00 ( 0.00%) 90.00 (-2.00%) 90.00 (-2.00%) 91.00 (-1.00%)
>
> Success figures across the board are broadly similar.
>
> traceonly-v2r2 lowlumpy-v2r3 waitcongest-v2r3waitwriteback-v2r4
> Direct reclaims 1045 944 886 887
> Direct reclaim pages scanned 135091 119604 109382 101019
> Direct reclaim pages reclaimed 88599 47535 47863 46671
> Direct reclaim write file async I/O 494 283 465 280
> Direct reclaim write anon async I/O 29357 13710 16656 13462
> Direct reclaim write file sync I/O 154 2 2 3
> Direct reclaim write anon sync I/O 14594 571 509 561
> Wake kswapd requests 7491 933 872 892
> Kswapd wakeups 814 778 731 780
> Kswapd pages scanned 7290822 15341158 11916436 13703442
> Kswapd pages reclaimed 3587336 3142496 3094392 3187151
> Kswapd reclaim write file async I/O 91975 32317 28022 29628
> Kswapd reclaim write anon async I/O 1992022 789307 829745 849769
> Kswapd reclaim write file sync I/O 0 0 0 0
> Kswapd reclaim write anon sync I/O 0 0 0 0
> Time stalled direct reclaim (seconds) 4588.93 2467.16 2495.41 2547.07
> Time kswapd awake (seconds) 2497.66 1020.16 1098.06 1176.82
>
> Total pages scanned 7425913 15460762 12025818 13804461
> Total pages reclaimed 3675935 3190031 3142255 3233822
> %age total pages scanned/reclaimed 49.50% 20.63% 26.13% 23.43%
> %age total pages scanned/written 28.66% 5.41% 7.28% 6.47%
> %age file pages scanned/written 1.25% 0.21% 0.24% 0.22%
> Percentage Time Spent Direct Reclaim 57.33% 42.15% 42.41% 42.99%
> Percentage Time kswapd Awake 43.56% 27.87% 29.76% 31.25%
>
> Scanned/reclaimed ratios again look good with big improvements in
> efficiency. The Scanned/written ratios also look much improved. With a
> better scanned/written ration, there is an expectation that IO would be more
> efficient and indeed, the time spent in direct reclaim is much reduced by
> the full series and kswapd spends a little less time awake.
>
> Overall, indications here are that allocations were
> happening much faster and this can be seen with a graph of
> the latency figures as the allocations were taking place
> http://www.csn.ul.ie/~mel/postings/vmscanreduce-20101509/highalloc-interlatency-hydra-mean.ps
>
> FTrace Reclaim Statistics: congestion_wait
> Direct number congest waited 1333 204 169 4
> Direct time congest waited 78896ms 8288ms 7260ms 200ms
> Direct full congest waited 756 92 69 2
> Direct number conditional waited 0 0 26 186
> Direct time conditional waited 0ms 0ms 0ms 2504ms
> Direct full conditional waited 0 0 0 25
> KSwapd number congest waited 4 395 227 282
> KSwapd time congest waited 384ms 25136ms 10508ms 18380ms
> KSwapd full congest waited 3 232 98 176
> KSwapd number conditional waited 0 0 0 0
> KSwapd time conditional waited 0ms 0ms 0ms 0ms
> KSwapd full conditional waited 0 0 0 0
> KSwapd full conditional waited 318 0 312 9
>
>
> Overall, the time spent speeping is reduced. kswapd is still hitting
> congestion_wait() but that is because there are callers remaining where it
> wasn't clear in advance if they should be changed to wait_iff_congested()
> or not. Overall the sleep imes are reduced though - from 79ish seconds to
> about 19.
>
> MMTests Statistics: duration
> User/Sys Time Running Test (seconds) 3415.43 3386.65 3388.39 3377.5
> Total Elapsed Time (seconds) 5733.48 3660.33 3689.41 3765.39
>
> With the full series, the time to complete the tests are reduced by 30%
>
> PPC64 STRESS-HIGHALLOC
> traceonly-v2r2 lowlumpy-v2r3 waitcongest-v2r3waitwriteback-v2r4
> Pass 1 17.00 ( 0.00%) 34.00 (17.00%) 38.00 (21.00%) 43.00 (26.00%)
> Pass 2 25.00 ( 0.00%) 37.00 (12.00%) 42.00 (17.00%) 46.00 (21.00%)
> At Rest 49.00 ( 0.00%) 43.00 (-6.00%) 45.00 (-4.00%) 51.00 ( 2.00%)
>
> Success rates there are *way* up particularly considering that the 16MB
> huge pages on PPC64 mean that it's always much harder to allocate them.
>
> FTrace Reclaim Statistics: vmscan
> stress-highalloc stress-highalloc stress-highalloc stress-highalloc
> traceonly-v2r2 lowlumpy-v2r3 waitcongest-v2r3waitwriteback-v2r4
> Direct reclaims 499 505 564 509
> Direct reclaim pages scanned 223478 41898 51818 45605
> Direct reclaim pages reclaimed 137730 21148 27161 23455
> Direct reclaim write file async I/O 399 136 162 136
> Direct reclaim write anon async I/O 46977 2865 4686 3998
> Direct reclaim write file sync I/O 29 0 1 3
> Direct reclaim write anon sync I/O 31023 159 237 239
> Wake kswapd requests 420 351 360 326
> Kswapd wakeups 185 294 249 277
> Kswapd pages scanned 15703488 16392500 17821724 17598737
> Kswapd pages reclaimed 5808466 2908858 3139386 3145435
> Kswapd reclaim write file async I/O 159938 18400 18717 13473
> Kswapd reclaim write anon async I/O 3467554 228957 322799 234278
> Kswapd reclaim write file sync I/O 0 0 0 0
> Kswapd reclaim write anon sync I/O 0 0 0 0
> Time stalled direct reclaim (seconds) 9665.35 1707.81 2374.32 1871.23
> Time kswapd awake (seconds) 9401.21 1367.86 1951.75 1328.88
>
> Total pages scanned 15926966 16434398 17873542 17644342
> Total pages reclaimed 5946196 2930006 3166547 3168890
> %age total pages scanned/reclaimed 37.33% 17.83% 17.72% 17.96%
> %age total pages scanned/written 23.27% 1.52% 1.94% 1.43%
> %age file pages scanned/written 1.01% 0.11% 0.11% 0.08%
> Percentage Time Spent Direct Reclaim 44.55% 35.10% 41.42% 36.91%
> Percentage Time kswapd Awake 86.71% 43.58% 52.67% 41.14%
>
> While the scanning rates are slightly up, the scanned/reclaimed and
> scanned/written figures are much improved. The time spent in direct reclaim
> and with kswapd are massively reduced, mostly by the lowlumpy patches.
>
> FTrace Reclaim Statistics: congestion_wait
> Direct number congest waited 725 303 126 3
> Direct time congest waited 45524ms 9180ms 5936ms 300ms
> Direct full congest waited 487 190 52 3
> Direct number conditional waited 0 0 200 301
> Direct time conditional waited 0ms 0ms 0ms 1904ms
> Direct full conditional waited 0 0 0 19
> KSwapd number congest waited 0 2 23 4
> KSwapd time congest waited 0ms 200ms 420ms 404ms
> KSwapd full congest waited 0 2 2 4
> KSwapd number conditional waited 0 0 0 0
> KSwapd time conditional waited 0ms 0ms 0ms 0ms
> KSwapd full conditional waited 0 0 0 0
>
>
> Not as dramatic a story here but the time spent asleep is reduced and we can still
> see what wait_iff_congested is going to sleep when necessary.
>
> MMTests Statistics: duration
> User/Sys Time Running Test (seconds) 12028.09 3157.17 3357.79 3199.16
> Total Elapsed Time (seconds) 10842.07 3138.72 3705.54 3229.85
>
> The time to complete this test goes way down. With the full series, we are allocating
> over twice the number of huge pages in 30% of the time and there is a corresponding
> impact on the allocation latency graph available at.
>
> http://www.csn.ul.ie/~mel/postings/vmscanreduce-20101509/highalloc-interlatency-powyah-mean.ps
>
> I think this series is ready for much wider testing. The lowlumpy patches in
> particular should be relatively uncontroversial. While their largest impact
> can be seen in the high order stress tests, they would also have an impact
> if SLUB was configured (these tests are based on slab) and stalls in lumpy
> reclaim could be partially responsible for some desktop stalling reports.
>
> The congestion_wait avoidance stuff was controversial in v1 because the
> heuristic used to avoid the wait was a bit shaky. I'm expecting that this
> version is more predictable.
>
> .../trace/postprocess/trace-vmscan-postprocess.pl | 39 +++-
> include/linux/backing-dev.h | 2 +-
> include/linux/mmzone.h | 8 +
> include/trace/events/vmscan.h | 44 ++++-
> include/trace/events/writeback.h | 35 +++
> mm/backing-dev.c | 66 ++++++-
> mm/page_alloc.c | 4 +-
> mm/vmscan.c | 226 ++++++++++++++------
> 8 files changed, 341 insertions(+), 83 deletions(-)
>
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--
Grüsse / regards, Christian Ehrhardt
IBM Linux Technology Center, System z Linux Performance
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