From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id E15E4600580 for ; Thu, 7 Jan 2010 11:37:15 -0500 (EST) Date: Thu, 7 Jan 2010 10:36:52 -0600 (CST) From: Christoph Lameter Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() In-Reply-To: Message-ID: References: <20100104182429.833180340@chello.nl> <20100104182813.753545361@chello.nl> <20100105054536.44bf8002@infradead.org> <20100105192243.1d6b2213@infradead.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Linus Torvalds Cc: Arjan van de Ven , Peter Zijlstra , "Paul E. McKenney" , Peter Zijlstra , KAMEZAWA Hiroyuki , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "minchan.kim@gmail.com" , "hugh.dickins" , Nick Piggin , Ingo Molnar List-ID: On Thu, 7 Jan 2010, Linus Torvalds wrote: > You're missing what Arjan said - the jav workload does a lot of memory > allocations too, causing mmap/munmap. Well isnt that tunable on the app level? Get bigger chunks of memory in order to reduce the frequency of mmap operations? If you want concurrency of faults then mmap_sem write locking currently needs to be limited. > So now some paths are indeed holding it for writing (or need to wait for > it to become writable). And the fairness of rwsems quite possibly then > impacts throughput a _lot_.. Very true. Doing range locking (maybe using the split pte lock boundaries, shifting some state from mm_struct into vmas) may be a way to avoid hold mmap_sem for write in that case. > (Side note: I wonder if we should wake up _all_ readers when we wake up > any. Right now, we wake up all readers - but only until we hit a writer. > Which is the _fair_ thing to do, but it does mean that we can end up in > horrible patterns of alternating readers/writers, when it could be much > better to just say "release the hounds" and let all pending readers go > after a writer has had its turn). Have a cycle with concurrent readers followed by a cycle of serialized writers may be best under heavy load. The writers need to be limited in frequency otherwise they will starve the readers. -- 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