Re: [PATCH 1/2] mm/madvise: allow process_madvise operations on entire memory range

[Suren Baghdasaryan]

On Tue, Dec 22, 2020 at 11:57 PM Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Tue, Dec 22, 2020 at 09:48:43AM -0800, Suren Baghdasaryan wrote:
> > Thanks for the feedback! The use case is userspace memory reaping
> > similar to oom-reaper. Detailed justification is here:
> > https://lore.kernel.org/linux-mm/20201124053943.1684874-1-surenb@xxxxxxxxxx
>
> Given that this new variant of process_madvise
>
>   a) does not work on an address range

True, however I can see other madvise flavors that could be used on
the entire process. For example process_madvise(MADV_PAGEOUT) could be
used to "shrink" an entire inactive background process.

>   b) is destructive

I agree that memory reaping might be the only case when a destructive
process_madvise() makes sense. Unless the target process is dying, a
destructive process_madvise() would need coordination with the target
process, and if it's coordinated then the target might as well call
normal madvise() itself.

>   c) doesn't share much code at all with the rest of process_madvise

It actually does reuse a considerable part of the code, but the same
code can be refactored and reused either way.

>
> Why not add a proper separate syscall?

I think my answer to (a) is one justification for allowing
process_madvise() to operate on the entire process. Also MADV_DONTNEED
seems quite suitable for this operation.
Considering the above answers, are you still leaning towards a separate syscall?

>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx.
>