Re: [PATCH] zram: update zram to use zpool

From: Austin S. Hemmelgarn
Date: Fri Jun 17 2016 - 08:28:24 EST


On 2016-06-17 04:30, Vitaly Wool wrote:
Hi Minchan,

On Thu, Jun 16, 2016 at 1:17 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
On Wed, Jun 15, 2016 at 10:42:07PM +0800, Geliang Tang wrote:
Change zram to use the zpool api instead of directly using zsmalloc.
The zpool api doesn't have zs_compact() and zs_pool_stats() functions.
I did the following two things to fix it.
1) I replace zs_compact() with zpool_shrink(), use zpool_shrink() to
call zs_compact() in zsmalloc.
2) The 'pages_compacted' attribute is showed in zram by calling
zs_pool_stats(). So in order not to call zs_pool_state() I move the
attribute to zsmalloc.

Signed-off-by: Geliang Tang <geliangtang@xxxxxxxxx>

NACK.

I already explained why.
http://lkml.kernel.org/r/20160609013411.GA29779@bbox

This is a fair statement, to a certain extent. I'll let Geliang speak
for himself but I am personally interested in this zram extension
because I want it to work on MMU-less systems. zsmalloc can not handle
that, so I want to be able to use zram over z3fold.
I concur with this.

It's also worth pointing out that people can and do use zram for things other than swap, so the assumption that zswap is a viable alternative is not universally correct. In my case for example, I use it on a VM host for temporary storage for transient SSI VM's. Making it more deterministic would be seriously helpful in this case, as it would mean I can more precisely provision resources on this particular system, and could better account for latencies in the testing these transient VM's are used for.