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

[Chen Feng <puck.chen@hisilicon.com>]

On 2016/3/3 9:56, Jerry Lee wrote:
> Hi,
> 
> Thanks for sharing the same experience and workaround with me.
> But it's kind of hard for me to set all the possible processes to no-kswapd flag
> in advance so that they would not trigger kswapd in the future.
> 
> Cheers,
> - Jerry
> 
> On 2 March 2016 at 22:21, chen feng <puck.chen@foxmail.com <mailto:puck.chen@foxmail.com>> wrote:
> 
> 
> 
>     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
>     >

Just hack the process who tigger it too frequenctly.
> 
> 

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