From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: deferred rss update instead of sloppy rss From: Benjamin Herrenschmidt In-Reply-To: References: <20041122141148.1e6ef125.akpm@osdl.org> Content-Type: text/plain Date: Tue, 23 Nov 2004 09:17:24 +1100 Message-Id: <1101161844.13598.133.camel@gaston> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Andrew Morton , hugh@veritas.com, Linus Torvalds , nickpiggin@yahoo.com.au, linux-mm@kvack.org, linux-ia64@vger.kernel.org, Linux Kernel list List-ID: On Mon, 2004-11-22 at 14:13 -0800, Christoph Lameter wrote: > On Mon, 22 Nov 2004, Andrew Morton wrote: > > > hrm. I cannot see anywhere in this patch where you update task_struct.rss. > > This is just the piece around it dealing with rss. The updating of rss > happens in the generic code. The change to that is trivial. I can repost > the whole shebang if you want. > > > > + /* only holding mmap_sem here maybe get page_table_lock too? */ > > > + mm->rss += tsk->rss; > > > + tsk->rss = 0; > > > up_read(&mm->mmap_sem); > > > > mmap_sem needs to be held for writing, surely? > > If there are no page faults occurring anymore then we would not need to > get the lock. Q: Is it safe to assume that no faults occur > anymore at this point? Why wouldn't the mm take faults on other CPUs ? (other threads) > > just to prevent transient gross inaccuracies. For some value of "16". > > The page fault code only increments rss. For larger transactions that > increase / decrease rss significantly the page_table_lock is taken and > mm->rss is updated directly. So no > gross inaccuracies can result. > -- > 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/ . > Don't email: aart@kvack.org -- Benjamin Herrenschmidt -- 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/ . Don't email: aart@kvack.org