Re: [PATCH] drm/ttm: stop warning on TT shrinker failure

[Michal Hocko <mhocko@suse.com>]

On Tue 23-03-21 14:06:25, Christian König wrote:
> Am 23.03.21 um 13:37 schrieb Michal Hocko:
> > On Tue 23-03-21 13:21:32, Christian König wrote:
[...]
> > > Ideally I would like to be able to trigger swapping out the shmem page I
> > > allocated immediately after doing the copy.
> > So let me try to rephrase to make sure I understand. You would like to
> > swap out the existing content from the shrinker and you use shmem as a
> > way to achieve that. The swapout should happen at the time of copying
> > (shrinker context) or shortly afterwards?
> > 
> > So effectively to call pageout() on the shmem page after the copy?
> 
> Yes, exactly that.

OK, good. I see what you are trying to achieve now. I do not think we
would want to allow pageout from the shrinker's context but what you can
do is to instantiate the shmem page into the tail of the inactive list
so the next reclaim attempt will swap it out (assuming swap is available
of course).

This is not really something that our existing infrastructure gives you
though, I am afraid. There is no way to tell a newly allocated shmem
page should be in fact cold and the first one to swap out. But there are
people more familiar with shmem and its pecularities so I might be wrong
here.

Anyway, I am wondering whether the overall approach is sound. Why don't
you simply use shmem as your backing storage from the beginning and pin
those pages if they are used by the device?

-- 
Michal Hocko
SUSE Labs