From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4615A22A.7040909@yahoo.com.au> Date: Fri, 06 Apr 2007 11:28:10 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: missing madvise functionality References: <46128051.9000609@redhat.com> <461357C4.4010403@yahoo.com.au> <46154226.6080300@redhat.com> In-Reply-To: <46154226.6080300@redhat.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: Ulrich Drepper , Andrew Morton , Linux Kernel , Jakub Jelinek , Linux Memory Management List-ID: Rik van Riel wrote: > Nick Piggin wrote: > >> Oh, also: something like this patch would help out MADV_DONTNEED, as it >> means it can run concurrently with page faults. I think the locking will >> work (but needs forward porting). > > > Ironically, your patch decreases throughput on my quad core > test system, with Jakub's test case. > > MADV_DONTNEED, my patch, 10000 loops (14k context switches/second) > > real 0m34.890s > user 0m17.256s > sys 0m29.797s > > > MADV_DONTNEED, my patch & your patch, 10000 loops (50 context > switches/second) > > real 1m8.321s > user 0m20.840s > sys 1m55.677s > > I suspect it's moving the contention onto the page table lock, > in zap_pte_range(). I guess that the thread private memory > areas must be living right next to each other, in the same > page table lock regions :) > > For more real world workloads, like the MySQL sysbench one, > I still suspect that your patch would improve things. I think it definitely would, because the app will be wanting to do other things with mmap_sem as well (like futexes *grumble*). Also, the test case is allocating and freeing 512K chunks, which I think would be on the high side of typical. You have 32 threads for 4 CPUs, so then it would actually make sense to context switch on mmap_sem write lock rather than spin on ptl. But the kernel doesn't know that. Testing with a small chunk size or thread == CPUs I think would show a swing toward my patch. -- SUSE Labs, Novell Inc. -- 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: email@kvack.org