Re: [PATCH v2] drm/i915: Disable shrinker for non-swapped backed objects

[Johannes Weiner <hannes@cmpxchg.org>]

On Thu, Nov 26, 2015 at 11:25:14AM +0000, Chris Wilson wrote:
> On Wed, Nov 25, 2015 at 03:46:35PM -0500, Johannes Weiner wrote:
> > On Wed, Nov 25, 2015 at 08:31:02PM +0000, Chris Wilson wrote:
> > > On Wed, Nov 25, 2015 at 02:06:10PM -0500, Johannes Weiner wrote:
> > > > On Wed, Nov 25, 2015 at 06:36:56PM +0000, Chris Wilson wrote:
> > > > > +static bool swap_available(void)
> > > > > +{
> > > > > +	return total_swap_pages || frontswap_enabled;
> > > > > +}
> > > > 
> > > > If you use get_nr_swap_pages() instead of total_swap_pages, this will
> > > > also stop scanning objects once the swap space is full. We do that in
> > > > the VM to stop scanning anonymous pages.
> > > 
> > > Thanks. Would EXPORT_SYMBOL_GPL(nr_swap_pages) (or equivalent) be
> > > acceptable?
> > 
> > No opposition from me. Just please add a small comment that this is
> > for shrinkers with swappable objects.
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 58877312cf6b..1c7861f4c43c 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -48,6 +48,14 @@ static sector_t map_swap_entry(swp_entry_t, struct block_device**);
>  DEFINE_SPINLOCK(swap_lock);
>  static unsigned int nr_swapfiles;
>  atomic_long_t nr_swap_pages;
> +/*
> + * Some modules use swappable objects and may try to swap them out under
> + * memory pressure (via the shrinker). Before doing so, they may wish to
> + * check to see if any swap space is available. The shrinker also directly
> + * uses the available swap space to determine whether it can swapout
> + * anon pages in the same manner.
> + */
> +EXPORT_SYMBOL_GPL(nr_swap_pages);
> 
> Something like that, after a couple more edits?

The last sentence isn't necessary IMO, but other than that it looks
good to me.
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