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

[Jerry Lee <leisurelysw24@gmail.com>]

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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> 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
> >
>

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