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SubjectRe: [PATCH v5 0/4] fadvise(DONTNEED) support
* MinChan Kim <minchan.kim@gmail.com> [2011-02-18 00:08:18]:

> Sorry for my laziness. It's time to repost with some test result.
>
> Recently, there was a reported problem about thrashing.
> (http://marc.info/?l=rsync&m=128885034930933&w=2)
> It happens by backup workloads(ex, nightly rsync).
> That's because the workload makes just use-once pages
> and touches pages twice. It promotes the page into
> active list so that it results in working set page eviction.
> So app developer want to support POSIX_FADV_NOREUSE but other OSes include linux
> don't support it. (http://marc.info/?l=linux-mm&m=128928979512086&w=2)
>
> By other approach, app developers use POSIX_FADV_DONTNEED.
> But it has a problem. If kernel meets page is going on writing
> during invalidate_mapping_pages, it can't work.
> It makes application programmer to use it hard since they always
> consider sync data before calling fadivse(..POSIX_FADV_DONTNEED) to
> make sure the pages couldn't be discardable. At last, they can't use
> deferred write of kernel so see performance loss.
> (http://insights.oetiker.ch/linux/fadvise.html)
>
> In fact, invalidation is very big hint to reclaimer.
> It means we don't use the page any more. So the idea in this series is that
> let's move invalidated pages but not-freed page until into inactive list.
> It can help relcaim efficiency very much so that it can prevent
> eviction working set.
>
> My exeperiment is folowing as.
>
> Test Environment :
> DRAM : 2G, CPU : Intel(R) Core(TM)2 CPU
> Rsync backup directory size : 16G
>
> rsync version is 3.0.7.
> rsync patch is Ben's fadivse.
> The stress scenario do following jobs with parallel.
>
> 1. git clone linux-2.6
> 1. make all -j4 linux-mmotm
> 3. rsync src dst
>
> nrns : no-patched rsync + no stress
> prns : patched rsync + no stress
> nrs : no-patched rsync + stress
> prs : patched rsync + stress
>
> For profiling, I add some vmstat.
> pginvalidate : the total number of pages which are moved by this patch.
> pgreclaim : the number of pages which are moved at inactive's tail by PG_reclaim of pginvalidate
>
> NRNS PRNS NRS PRS
> Elapsed time 36:01.49 37:13.58 01:23:24 01:21:45
> nr_vmscan_write 184 1 296 509
> pgactivate 76559 84714 445214 463143
> pgdeactivate 19360 40184 74302 91423
> pginvalidate 0 2240333 0 1769147
> pgreclaim 0 1849651 0 1650796
> pgfault 406208 421860 72485217 70334416
> pgmajfault 212 334 5149 3688
> pgsteal_dma 0 0 0 0
> pgsteal_normal 2645174 1545116 2521098 1578651
> pgsteal_high 5162080 2562269 6074720 3137294
> pgsteal_movable 0 0 0 0
> pgscan_kswapd_dma 0 0 0 0
> pgscan_kswapd_normal 2641732 1545374 2499894 1557882
> pgscan_kswapd_high 5143794 2567981 5999585 3051150
> pgscan_kswapd_movable 0 0 0 0
> pgscan_direct_dma 0 0 0 0
> pgscan_direct_normal 3643 0 21613 21238
> pgscan_direct_high 20174 1783 76980 87848
> pgscan_direct_movable 0 0 0 0
> pginodesteal 130 1029 3510 24100
> slabs_scanned 1421824 1648128 1870720 1880320
> kswapd_steal 7785153 4105620 8498332 4608372
> kswapd_inodesteal 189432 474052 342835 472503
> pageoutrun 100687 52282 145712 70946
> allocstall 22 1 149 163
> pgrotated 0 2231408 2932 1765393
> unevictable_pgs_scanned 0 0 0 0
>

The results do look impressive


--
Three Cheers,
Balbir


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