On Fri, Mar 18, 2022 at 12:51:14PM -0400, Brian Geffon wrote:

On Fri, Mar 18, 2022 at 12:41 PM Minchan Kim [off-list ref] wrote:

quoted

On Tue, Mar 15, 2022 at 10:22:21AM -0700, Brian Geffon wrote:

quoted

Today it's only possible to write back as a page, idle, or huge.
A user might want to writeback pages which are huge and idle first
as these idle pages do not require decompression and make a good
first pass for writeback.

Hi Brian,

I am not sure how much the decompression overhead matter for idle pages
writeback since it's already *very slow* path in zram but I agree that
it would be a good first pass since the memory saving for huge writing
would be cost efficient.

Just out of curiosity. Do you have real usecase?

Hi Minchan,
Thank you for taking a look. When we are thinking about writeback
we're trying to be very sensitive to our devices storage endurance,
for this reason we will have a fairly conservative writeback limit.
Given that, we want to make sure we're maximizing what lands on disk
while still minimizing the refault time. We could take the approach
where we always writeback huge pages but then we may result in very
quick refaults which would be a huge waste of time. So idle writeback
is a must for us and being able to writeback the pages which have
maximum value (huge) would be very useful.

Thanks for sharing the thought. It really make sense to me and
would be great if it goes on the description.