Re: [PATCH 0/9] Reduce system disruption due to kswapd V4

[Zlatko Calusic]

On 15.05.2013 22:37, Andrew Morton wrote:
> >                              3.10.0-rc1  3.10.0-rc1
> >                                 vanilla lessdisrupt-v4
> > Page Ins                       1234608      101892
> > Page Outs                     12446272    11810468
> > Swap Ins                        283406           0
> > Swap Outs                       698469       27882
> > Direct pages scanned                 0      136480
> > Kswapd pages scanned           6266537     5369364
> > Kswapd pages reclaimed         1088989      930832
> > Direct pages reclaimed               0      120901
> > Kswapd efficiency                  17%         17%
> > Kswapd velocity               5398.371    4635.115
> > Direct efficiency                 100%         88%
> > Direct velocity                  0.000     117.817
> > Percentage direct scans             0%          2%
> > Page writes by reclaim         1655843     4009929
> > Page writes file                957374     3982047
> > Page writes anon                698469       27882
> > Page reclaim immediate            5245        1745
> > Page rescued immediate               0           0
> > Slabs scanned                    33664       25216
> > Direct inode steals                  0           0
> > Kswapd inode steals              19409         778
>
> The reduction in inode steals might be a significant thing?
> prune_icache_sb() does invalidate_mapping_pages() and can have the bad
> habit of shooting down a vast number of pagecache pages (for a large
> file) in a single hit.  Did this workload use large (and clean) files?
> Did you run any test which would expose this effect?

I did not run specific tests, but I believe I observed exactly this 
issue on the real workload, where even at a moderate load sudden frees 
of pagecache happen quite often. I've attached a small graph where it 
can be easily seen. The snapshot was taken while the server was running 
an unpatched Linus kernel. After the Mel's patch series is applied, I 
can't see anything similar. So it seems that this issue is completely 
gone, Mel's done a wonderful job.

And BTW, V4 continues to be rock stable, running here on many different 
machines, so I look forward seeing this code merged in 3.11.
--
Zlatko

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