* MinChan Kim [off-list ref] [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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