Re: [PATCH] drm/i915: Revert shrinker changes from "Track unbound pages"

[Chris Wilson <chris@chris-wilson.co.uk>]

On Wed,  9 Jan 2013 18:57:09 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> This partially reverts
> 
> commit 6c085a728cf000ac1865d66f8c9b52935558b328
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date:   Mon Aug 20 11:40:46 2012 +0200
> 
>     drm/i915: Track unbound pages
> 
> Closer inspection of that patch revealed a bunch of unrelated changes
> in the shrinker:
> - The shrinker count is now in pages instead of objects.
> - For counting the shrinkable objects the old code only looked at the
>   inactive list, the new code looks at all bounds objects (including
>   pinned ones). That is obviously in addition to the new unbound list.
> - The shrinker cound is no longer scaled with
>   sysctl_vfs_cache_pressure.

I made a mistake and copied the wrong code in my original
implementation:

vfs_cache_pressure
------------------

Controls the tendency of the kernel to reclaim the memory which is used for
caching of directory and inode objects.

At the default value of vfs_cache_pressure=100 the kernel will attempt to
reclaim dentries and inodes at a "fair" rate with respect to pagecache and
swapcache reclaim.  Decreasing vfs_cache_pressure causes the kernel to prefer
to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
never reclaim dentries and inodes due to memory pressure and this can easily
lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
causes the kernel to prefer to reclaim dentries and inodes.

--------------------

It's not an inode or a directory and our pages directly akin to the page
and buffer caches, so I should have never used vfs_cache_pressure and
you have not justified why you are adding it back.

> - When actually shrinking objects, the old code first dropped
>   purgeable objects, then normal (inactive) objects. Only then did it,
>   in a last-ditch effort idle the gpu and evict everything. The new
>   code omits the intermediate step of evicting normal inactive
>   objects.

This is the crux of the papering, so just do this and call it what it is.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre