From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [RFC v1][PATCH]page_fault retry with NOPAGE_RETRY From: Peter Zijlstra In-Reply-To: <492E6849.6090205@google.com> References: <604427e00811212247k1fe6b63u9efe8cfe37bddfb5@mail.gmail.com> <20081123091843.GK30453@elte.hu> <604427e00811251042t1eebded6k9916212b7c0c2ea0@mail.gmail.com> <20081126123246.GB23649@wotan.suse.de> <492DAA24.8040100@google.com> <20081127085554.GD28285@wotan.suse.de> <492E6849.6090205@google.com> Content-Type: text/plain Date: Thu, 27 Nov 2008 11:00:07 +0100 Message-Id: <1227780007.4454.1344.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Mike Waychison Cc: Nick Piggin , Ying Han , Ingo Molnar , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm , David Rientjes , Rohit Seth , Hugh Dickins , "H. Peter Anvin" , edwintorok@gmail.com List-ID: On Thu, 2008-11-27 at 01:28 -0800, Mike Waychison wrote: > Correct. I don't recall the numbers from the pathelogical cases we were > seeing, but iirc, it was on the order of 10s of seconds, likely > exascerbated by slower than usual disks. I've been digging through my > inbox to find numbers without much success -- we've been using a variant > of this patch since 2.6.11. > We generally try to avoid such things, but sometimes it a) can't be > easily avoided (third party libraries for instance) and b) when it hits > us, it affects the overall health of the machine/cluster (the monitoring > daemons get blocked, which isn't very healthy). If its only monitoring, there might be another solution. If you can keep the required data in a separate (approximate) copy so that you don't need mmap_sem at all to show them. If your mmap_sem is so contended your latencies are unacceptable, adding more users to it - even statistics gathering, just isn't going to cure the situation. Furthermore, /proc code usually isn't written with performance in mind, so its usually simple and robust code. Adding it to a 'hot'-path like you're doing doesn't seem advisable. Also, releasing and re-acquiring mmap_sem can significantly add to the cacheline bouncing that thing already has. -- 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