From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id qAS1B29Y118365 for ; Tue, 27 Nov 2012 19:11:02 -0600 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by cuda.sgi.com with ESMTP id 1KDwNoLegJZqVC5N for ; Tue, 27 Nov 2012 17:13:18 -0800 (PST) Message-Id: From: Chris Wilson Subject: Re: [PATCH 17/19] drivers: convert shrinkers to new count/scan API In-Reply-To: <1354058086-27937-18-git-send-email-david@fromorbit.com> References: <1354058086-27937-1-git-send-email-david@fromorbit.com> <1354058086-27937-18-git-send-email-david@fromorbit.com> Date: Wed, 28 Nov 2012 01:13:11 +0000 List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Dave Chinner , glommer@parallels.com Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com On Wed, 28 Nov 2012 10:14:44 +1100, Dave Chinner 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 _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs