Re: [REGRESSION][BISECTED] Unexpected OOM instead of reclaiming inactive file pages

[David Rientjes <rientjes@google.com>]

On Mon, 11 Aug 2025, Oleksandr Natalenko wrote:

> Hello Damien.
> 
> I'm fairly confident that the following commit
> 
> 459779d04ae8d block: Improve read ahead size for rotational devices
> 
> caused a regression in my test bench.
> 
> I'm running v6.17-rc1 in a small QEMU VM with virtio-scsi disk. It has got 1 GiB of RAM, so I can saturate it easily causing reclaiming mechanism to kick in.
> 
> If MGLRU is enabled:
> 
> $ echo 1000 | sudo tee /sys/kernel/mm/lru_gen/min_ttl_ms
> 
> then, once page cache builds up, an OOM happens without reclaiming inactive file pages: [1]. Note that inactive_file:506952kB, I'd expect these to be reclaimed instead, like how it happens with v6.16.
> 
> If MGLRU is disabled:
> 
> $ echo 0 | sudo tee /sys/kernel/mm/lru_gen/min_ttl_ms
> 
> then OOM doesn't occur, and things seem to work as usual.
> 
> If MGLRU is enabled, and 459779d04ae8d is reverted on top of v6.17-rc1, the OOM doesn't happen either.
> 
> Could you please check this?
> 

This looks to be an MGLRU policy decision rather than a readahead 
regression, correct?

Mem-Info:
active_anon:388 inactive_anon:5382 isolated_anon:0
 active_file:9638 inactive_file:126738 isolated_file:0

Setting min_ttl_ms to 1000 is preserving the working set and triggering 
the oom kill is the only alternative to free memory in that configuration.  
The oom kill is being triggered by kswapd for this purpose.

So additional readahead would certainly increase that working set.  This 
looks working as intended.