From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH] low-latency zap_page_range() From: Robert Love In-Reply-To: <3D6E8B7F.8D5D20D8@zip.com.au> References: <3D6E844C.4E756D10@zip.com.au> <1030653602.939.2677.camel@phantasy> <3D6E8B7F.8D5D20D8@zip.com.au> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: 29 Aug 2002 17:12:11 -0400 Message-Id: <1030655532.12110.2691.camel@phantasy> Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, 2002-08-29 at 17:00, Andrew Morton wrote: > That's an interesting point. page_table_lock is one of those locks > which is occasionally held for ages, and frequently held for a short > time. Since latency is a direct function of lock held times in the preemptible kernel, and I am seeing disgusting zap_page_range() latencies, the lock is held a long time. So we know it is held forever and a day... but is there contention? > But I don't recall seeing nasty page_table_lock spintimes on > anyone's lockmeter reports, so we can leave it as-is for now. I do not recall seeing this either and I have not done my own tests. Personally, I would love to rip out the "cond_resched_lock()" and just do spin_unlock(); spin_lock(); and be done with it. This gives automatic preemption support and the SMP benefit. Preemption being an "automatic" consequence of improved locking was always my selling point (albeit, this is a gross example of improving the locking, but it gets the job done). But, the current implementation was more palatable to you and Linus when I first posted this, and that counts for something. Robert Love -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/