Re: [PATCH v5 4/4] mm: Introduce per-thpsize swapin control policy

[Barry Song]

On Mon, Jul 29, 2024 at 3:52 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Fri, Jul 26, 2024 at 09:46:18PM +1200, Barry Song wrote:
> > A user space interface can be implemented to select different swap-in
> > order policies, similar to the mTHP allocation order policy. We need
> > a distinct policy because the performance characteristics of memory
> > allocation differ significantly from those of swap-in. For example,
> > SSD read speeds can be much slower than memory allocation. With
> > policy selection, I believe we can implement mTHP swap-in for
> > non-SWAP_SYNCHRONOUS scenarios as well. However, users need to understand
> > the implications of their choices. I think that it's better to start
> > with at least always never. I believe that we will add auto in the
> > future to tune automatically, which can be used as default finally.
>
> I strongly disagree.  Use the same sysctl as the other anonymous memory
> allocations.

In versions v1-v4, we used the same controls as anonymous memory allocations.
Ying expressed concerns that this approach isn't always ideal, especially for
non-zRAM devices, as SSD read speeds can be much slower than memory
allocation. I think his concern is reasonable to some extent.

However, this patchset only addresses scenarios involving zRAM-like devices
and will not impact SSDs. I would like to get Ying's feedback on whether
it's acceptable to drop this one in v6.

Thanks
Barry