From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 29 Feb 2008 22:23:27 +0100 From: Andrea Arcangeli Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges Message-ID: <20080229212327.GC8091@v2.random> References: <20080228005249.GF8091@v2.random> <20080228011020.GG8091@v2.random> <20080229005530.GO8091@v2.random> <20080229131302.GT8091@v2.random> <20080229201744.GB8091@v2.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Nick Piggin , akpm@linux-foundation.org, Robin Holt , Avi Kivity , Izik Eidus , kvm-devel@lists.sourceforge.net, Peter Zijlstra , general@lists.openfabrics.org, Steve Wise , Roland Dreier , Kanoj Sarcar , steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, daniel.blueman@quadrics.com List-ID: On Fri, Feb 29, 2008 at 01:03:16PM -0800, Christoph Lameter wrote: > That means we need both the anon_vma locks and the i_mmap_lock to become > semaphores. I think semaphores are better than mutexes. Rik and Lee saw > some performance improvements because list can be traversed in parallel > when the anon_vma lock is switched to be a rw lock. The improvement was with a rw spinlock IIRC, so I don't see how it's related to this. Perhaps the rwlock spinlock can be changed to a rw semaphore without measurable overscheduling in the fast path. However theoretically speaking the rw_lock spinlock is more efficient than a rw semaphore in case of a little contention during the page fault fast path because the critical section is just a list_add so it'd be overkill to schedule while waiting. That's why currently it's a spinlock (or rw spinlock). > Sounds like we get to a conceptually clean version here? I don't have a strong opinion if it should become a semaphore unconditionally or only with a CONFIG_XPMEM=y. But keep in mind preempt-rt runs quite a bit slower, or we could rip spinlocks out of the kernel in the first place ;) -- 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