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

[Oleksandr Natalenko]

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?

Thank you.

-- 
Oleksandr Natalenko, MSE

[1]: https://paste.voidband.net/TG5OiZ29.log

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