Re: kswapd consumes 100% CPU when highest zone is small

[chen feng <puck.chen@foxmail.com>]

On 2016/3/2 14:20, Jerry Lee wrote:
> Hi,
> 
> I have a x86_64 system with 2G RAM using linux-3.12.x.  During copying
> large
> files (e.g. 100GB), kswapd easily consumes 100% CPU until the file is
> deleted
> or the page cache is dropped.  With setting the min_free_kbytes from 16384
> to
> 65536, the symptom is mitigated but I can't totally get rid of the problem.
> 
> After some trial and error, I found that highest zone is always unbalanced
> with
> order-0 page request so that pgdat_blanaced() continuously return false and
> kswapd can't sleep.
> 
> Here's the watermarks (min_free_kbytes = 65536) in my system:
> Node 0, zone      DMA
>   pages free     2167
>         min      138
>         low      172
>         high     207
>         scanned  0
>         spanned  4095
>         present  3996
>         managed  3974
> 
> Node 0, zone    DMA32
>   pages free     215375
>         min      16226
>         low      20282
>         high     24339
>         scanned  0
>         spanned  1044480
>         present  490971
>         managed  464223
> 
> Node 0, zone   Normal
>   pages free     7
>         min      18
>         low      22
>         high     27
>         scanned  0
>         spanned  1536
>         present  1536
>         managed  523
> 
> Besides, when the kswapd crazily spins, the value of the following entries
> in vmstat increases quickly even when I stop copying file:
> 
> pgalloc_dma 17719
> pgalloc_dma32 3262823
> slabs_scanned 937728
> kswapd_high_wmark_hit_quickly 54333233
> pageoutrun 54333235
> 
> Is there anything I could do to totally get rid of the problem?
> \
Yes, I have the same issue on arm64 platform.

I think you can increase the normal ZONE size. And I think there will be a memory alloc process
in your system which tigger the kswapd too frequently.

You can set this process to no-kswapd flag will also solve this issue.
> Thanks
> 

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