Re: [PATCH v6 0/9] Multigenerational LRU Framework

[Alexey Avramov]

Note that with vm.swappiness=0, the vm.watermark_scale_factor value does
not affect the swap possibility: MGLRU ignores sc->file_is_tiny.

With the classic 2-gen LRU swapping goes well at swappiness=0 and
high vm.watermark_scale_factor, which is expected according to the
documentation:
"At 0, the kernel will not initiate swap until the amount of free and
file-backed pages is less than the high watermark in a zone." [1]

With vm.swappiness=0, no swap occurs with any vm.watermark_scale_factor
value with MGLRU.

I used to see in practice (with MGLRU v3) the impossibility of swapping 
when vm.swappiness=0 and vm.watermark_scale_factor=1000.

At a minimum, this will require updating the documentation for
vm.swappiness.

BTW, why MGLRU doesn't use something like sc->file_is_tiny?

[1] https://github.com/torvalds/linux/blob/v5.16/Documentation/admin-guide/sysctl/vm.rst#swappiness