Re: [PATCH] mm/vmscan: add sysctl knobs for protecting the working set

[Andrew Morton]

On Thu, 2 Dec 2021 21:05:01 +0300 ValdikSS <iam@xxxxxxxxxxxxxxx> wrote:

> This patchset is surprisingly effective and very useful for low-end PC 
> with slow HDD, single-board ARM boards with slow storage, cheap Android 
> smartphones with limited amount of memory. It almost completely prevents 
> thrashing condition and aids in fast OOM killer invocation.
> 
> The similar file-locking patch is used in ChromeOS for nearly 10 years 
> but not on stock Linux or Android. It would be very beneficial for 
> lower-performance Android phones, SBCs, old PCs and other devices.
> 
> With this patch, combined with zram, I'm able to run the following 
> software on an old office PC from 2007 with __only 2GB of RAM__ 
> simultaneously:
> 
>   * Firefox with 37 active tabs (all data in RAM, no tab unloading)
>   * Discord
>   * Skype
>   * LibreOffice with the document opened
>   * Two PDF files (14 and 47 megabytes in size)
> 
> And the PC doesn't crawl like a snail, even with 2+ GB in zram!
> Without the patch, this PC is barely usable.
> Please watch the video:
> https://notes.valdikss.org.ru/linux-for-old-pc-from-2007/en/
> 

This is quite a condemnation of the current VM.  It shouldn't crawl
like a snail.

The patch simply sets hard limits on page reclaim's malfunctioning. 
I'd prefer that reclaim not malfunction :(

That being said, I can see that a blunt instrument like this would be
useful.

I don't think that the limits should be "N bytes on the current node". 
Nodes can have different amounts of memory so I expect it should scale
the hard limits on a per-node basis.  And of course, the various zones
have different size as well.

We do already have a lot of sysctls for controlling these sort of
things.  Was much work put into attempting to utilize the existing
sysctls to overcome these issues?