On Wed, 28 Nov 2012 10:14:44 +1100, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > +/* > + * XXX: (dchinner) This is one of the worst cases of shrinker abuse I've seen. > + * > + * i915_gem_purge() expects a byte count to be passed, and the minimum object > + * size is PAGE_SIZE. No, purge() expects a count of pages to be freed. Each pass of the shrinker therefore tries to free a minimum of 128 pages. > The shrinker doesn't work on bytes - it works on > + * *objects*. And I thought you were reviewing the shrinker API to be useful where a single object may range between 4K and 4G. > So it passes a nr_to_scan of 128 objects, which is interpreted > + * here to mean "free 128 bytes". That means a single object will be freed, as > + * the minimum object size is a page. > + * > + * But the craziest part comes when i915_gem_purge() has walked all the objects > + * and can't free any memory. That results in i915_gem_shrink_all() being > + * called, which idles the GPU and frees everything the driver has in it's > + * active and inactive lists. It's basically hitting the driver with a great big > + * hammer because it was busy doing stuff when something else generated memory > + * pressure. This doesn't seem particularly wise... > + */ As opposed to triggering an OOM? The choice was between custom code for a hopefully rare code path in a situation of last resort, or first implementing the simplest code that stopped i915 from starving the system of memory. -Chris -- Chris Wilson, Intel Open Source Technology Centre -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>