lkml.org 
[lkml]   [2012]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 0/2] Removal of lumpy reclaim
On Fri, Apr 06, 2012 at 12:34:39PM -0700, Andrew Morton wrote:
> On Wed, 28 Mar 2012 17:06:21 +0100
> Mel Gorman <mgorman@suse.de> wrote:
>
> > (cc'ing active people in the thread "[patch 68/92] mm: forbid lumpy-reclaim
> > in shrink_active_list()")
> >
> > In the interest of keeping my fingers from the flames at LSF/MM, I'm
> > releasing an RFC for lumpy reclaim removal.
>
> I grabbed them, thanks.
>

There probably will be a V2 as Ying pointed out a problem with patch 1.

> >
> > ...
> >
> > MMTests Statistics: vmstat
> > Page Ins 5426648 2840348 2695120
> > Page Outs 7206376 7854516 7860408
> > Swap Ins 36799 0 0
> > Swap Outs 76903 4 0
> > Direct pages scanned 31981 43749 160647
> > Kswapd pages scanned 26658682 1285341 1195956
> > Kswapd pages reclaimed 2248583 1271621 1178420
> > Direct pages reclaimed 6397 14416 94093
> > Kswapd efficiency 8% 98% 98%
> > Kswapd velocity 22134.225 1127.205 1051.316
> > Direct efficiency 20% 32% 58%
> > Direct velocity 26.553 38.367 141.218
> > Percentage direct scans 0% 3% 11%
> > Page writes by reclaim 6530481 4 0
> > Page writes file 6453578 0 0
> > Page writes anon 76903 4 0
> > Page reclaim immediate 256742 17832 61576
> > Page rescued immediate 0 0 0
> > Slabs scanned 1073152 971776 975872
> > Direct inode steals 0 196279 205178
> > Kswapd inode steals 139260 70390 64323
> > Kswapd skipped wait 21711 1 0
> > THP fault alloc 1 126 143
> > THP collapse alloc 324 294 224
> > THP splits 32 8 10
> > THP fault fallback 0 0 0
> > THP collapse fail 5 6 7
> > Compaction stalls 364 1312 1324
> > Compaction success 255 343 366
> > Compaction failures 109 969 958
> > Compaction pages moved 265107 3952630 4489215
> > Compaction move failure 7493 26038 24739
> >
> > ...
> >
> > Success rates are completely hosed for 3.4-rc1 which is almost certainly
> > due to [fe2c2a10: vmscan: reclaim at order 0 when compaction is enabled]. I
> > expected this would happen for kswapd and impair allocation success rates
> > (https://lkml.org/lkml/2012/1/25/166) but I did not anticipate this much
> > a difference: 95% less scanning, 43% less reclaim by kswapd
> >
> > In comparison, reclaim/compaction is not aggressive and gives up easily
> > which is the intended behaviour. hugetlbfs uses __GFP_REPEAT and would be
> > much more aggressive about reclaim/compaction than THP allocations are. The
> > stress test above is allocating like neither THP or hugetlbfs but is much
> > closer to THP.
>
> We seem to be thrashing around a bit with the performance, and we
> aren't tracking this closely enough.
>

Yes.

> What is kswapd efficiency? pages-relclaimed/pages-scanned?

pages_reclaimed*100/pages_scanned

> Why did it
> increase so much?

Lumpy reclaim increases the number of pages scanned in
isolate_lru_pages() and that is what I was attributing it to.

> Are pages which were reclaimed via prune_icache_sb()
> included? If so, they can make a real mess of the scanning efficiency
> metric.
>

I don't think so. For Kswapd efficiency, I'm using "kswapd_steal" from
vmstat and that is updated by shrink_inactive_list and not the slab
shrinker

> The increase in PGINODESTEAL is remarkable. It seems to largely be a
> transfer from kswapd inode stealing. Bad from a latency POV, at least.
> What would cause this change?

I'm playing catch-up at the moment and right now, I do not have a good
explanation as to why it changed like this. The most likely explanation
is that we are reclaiming fewer pages leading to more slab reclaim.

--
Mel Gorman
SUSE Labs


\
 
 \ /
  Last update: 2012-04-10 10:35    [from the cache]
©2003-2011 Jasper Spaans