On pe, 2017-06-09 at 12:03 +0100, Chris Wilson wrote:
> When we are called to relieve mempressue via the shrinker, the only way
> we can make progress is either by discarding unwanted pages (those
> objects that userspace has marked MADV_DONTNEED) or by reclaiming the
> dirty objects via swap. As we know that is the only way to make further
> progress, we can initiate the writeback as we invalidate the objects.
> This means the objects we put onto the inactive anon lru list are
> already marked for reclaim+writeback and so will trigger a wait upon the
> writeback inside direct reclaim, greatly improving the success rate of
> direct reclaim on i915 objects.
>
> The corollary is that we may start a slow swap on opportunistic
> mempressure from the likes of the compaction + migration kthreads. This
> is limited by those threads only being allowed to shrink idle pages, but
> also that if we reactivate the page before it is swapped out by gpu
> activity, we only page the cost of repinning the page. The cost is most
> felt when an object is reused after mempressure, which hopefully
> excludes the latency sensitive tasks (as we are just extending the
> impact of swap thrashing to them).
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
> Cc: Matthew Auld <matthew.a...@intel.com>
> Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
> Cc: Michal Hocko <mho...@suse.com>
<SNIP>
> +static void __start_writeback(struct drm_i915_gem_object *obj)
> +{
<SNIP>
> + /* Force any other users of this object to refault */
> + mapping = obj->base.filp->f_mapping;
> + unmap_mapping_range(mapping, 0, (loff_t)-1, 0);
> +
> + /* Begin writeback on each dirty page */
> + for (i = 0; i < obj->base.size >> PAGE_SHIFT; i++) {
> + struct page *page;
> +
> + page = find_lock_entry(mapping, i);
> + if (!page || radix_tree_exceptional_entry(page))
> + continue;
> +
> + if (!page_mapped(page) && clear_page_dirty_for_io(page)) {
> + int ret;
> +
> + SetPageReclaim(page);
> + ret = mapping->a_ops->writepage(page, &wbc);
> + if (!PageWriteback(page))
> + ClearPageReclaim(page);
> + if (!ret)
> + goto put;
> + }
> + unlock_page(page);
> +put:
> + put_page(page);
> + }
Apart from this part (which should probably be a helper function
outside of i915), the code is:
Reviewed-by: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
Regards, Joonas
--
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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