Re: [PATCH v6] mm/ksm: introduce ksm_force for each process

[Andrew Morton]

On Tue, 10 May 2022 15:30:36 +0200 Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx> wrote:

> > If ksm_force is set to 1, force all anonymous and 'qualified' VMAs
> > of this mm to be involved in KSM scanning without explicitly calling
> > madvise to mark VMA as MADV_MERGEABLE. But It is effective only when
> > the klob of /sys/kernel/mm/ksm/run is set as 1.
> > 
> > If ksm_force is set to 0, cancel the feature of ksm_force of this
> > process (fallback to the default state) and unmerge those merged pages
> > belonging to VMAs which is not madvised as MADV_MERGEABLE of this process,
> > but still leave MADV_MERGEABLE areas merged.
> 
> To my best knowledge, last time a forcible KSM was discussed (see threads [1], [2], [3] and probably others) it was concluded that a) procfs was a horrible interface for things like this one; and b) process_madvise() syscall was among the best suggested places to implement this (which would require a more tricky handling from userspace, but still).
> 
> So, what changed since that discussion?
> 
> P.S. For now I do it via dedicated syscall, but I'm not trying to upstream this approach.

Why are you patching the kernel with a new syscall rather than using
process_madvise()?