Re: [Bug 213299] New: kswapd Regression as of 5.13-rc3, eats 100% of CPU for no reason

[Andrew Morton <akpm@linux-foundation.org>]

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Mon, 31 May 2021 18:09:38 +0000 bugzilla-daemon@bugzilla.kernel.org wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=213299
> 
>             Bug ID: 213299
>            Summary: kswapd Regression as of 5.13-rc3, eats 100% of CPU for
>                     no reason
>            Product: Memory Management
>            Version: 2.5
>     Kernel Version: 5.13-rc3, 5.13-rc4
>           Hardware: All
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: Slab Allocator
>           Assignee: akpm@linux-foundation.org
>           Reporter: gardotd426@gmail.com
>         Regression: No
> 
> I've seen reports of kswapd0 eating up CPU, but this doesn't fit those
> descriptions. 
> 
>  - The bug is not present on 5.12.
> 
>  - It happens immediately on boot, CPU usage goes to 100 on all 24 threads of a
> Ryzen 5900X
> 
>  - The only solution is to run `sudo pkill -9 kswapd0`. swapoff does nothing,
> nor does `echo 1 > /proc/sys/vm/drop_caches`. 
> 
>  - I have a swap partition and 32GB of RAM. Like I said, this happens on boot,
> so nowhere *near* 32GB of RAM is being taken. And no swap is being used. This
> is clearly an error in kswapd, it's like it goes completely bonkers. 5.13-rc2
> didn't have it, nor did rc1, and 5.12 doesn't have it either. 
> 
> 
> System Info:
> 
> Arch Linux
> Kernel: 5.13-rc3, 5.13-rc4
> Ryzen 9 5900X
> 32GB DDR4-3600
> 40GB Swap partition on SSD
> 
> sudo dmesg | grep -i swap only gives these three lines so far (after already
> killing the process and about 5 min. after boot):
> 
> [    0.093277] Spectre V1 : Mitigation: usercopy/swapgs barriers and __user
> pointer sanitization
> [    0.334800] zswap: loaded using pool lz4/z3fold
> [    2.941371] Adding 41502716k swap on /dev/sdb3.  Priority:-2 extents:1
> across:41502716k SSFS
> 
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