From: Michal Hocko <mhocko@kernel.org>
To: Jerry Lee <leisurelysw24@gmail.com>
Cc: linux-mm@kvack.org
Subject: Re: kswapd consumes 100% CPU when highest zone is small
Date: Wed, 2 Mar 2016 18:36:40 +0100 [thread overview]
Message-ID: <20160302173639.GD26701@dhcp22.suse.cz> (raw)
In-Reply-To: <CAKQB+ft3q2O2xYG2CTmTM9OCRLCP2FPTfHQ3jvcFSM-FGrjgGA@mail.gmail.com>
On Wed 02-03-16 14:20:38, 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
The zone Normal is just too small and that confuses the reclaim path.
>
> 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?
I would try to sacrifice those few megs and get rid of zone normal
completely. AFAIR mem=4G should limit the max_pfn to 4G so DMA32 should
cover the shole memory.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2016-03-02 17:36 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-02 6:20 Jerry Lee
2016-03-02 14:21 ` chen feng
2016-03-03 1:56 ` Jerry Lee
2016-03-03 5:59 ` Chen Feng
2016-03-02 17:36 ` Michal Hocko [this message]
2016-03-03 2:23 ` Jerry Lee
2016-03-03 8:22 ` Michal Hocko
2016-03-03 9:27 ` Jerry Lee
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