From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 27 Feb 2006 08:43:52 -0800 (PST) From: Christoph Lameter Subject: Re: page_lock_anon_vma(): remove check for mapped page In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Hugh Dickins Cc: akpm@osdl.org, linux-mm@kvack.org List-ID: On Mon, 27 Feb 2006, Hugh Dickins wrote: > > At least my tests show that this codepath is valid and its for new > > functionality in 2.6.16. So I guess its suitable for 2.6.16. > > Well, it's certainly not for me to decide: I just didn't want my signoff > to be interpreted as a request to push it into 2.6.16. It seemed to me > rather late to be enabling this new functionality in 2.6.16, even though > it's a bug that it wasn't already enabled in 2.6.16-rc: you'll have to > argue that one without me. Perhaps it doesn't matter if the vast > majority have CONFIG_MIGRATION configured off. There are only a very few users of page migration since this is new functionality. Even those with CONFIG_MIGRATION need to do special modifications to their systems (installiing a new numactl package, setting up their cpusets differently) to use this functionality. Also the functionality in question has been available in the hotplug project in the past. > I'm not sure that I've understood your doubt correctly. But I think > you're missing that rcu_read_lock is just another name for preempt_disable, > plus we always disable preemption when taking a spin lock: so in effect > we have rcu_read_lock in force until the spin_unlock(&anon_vma->lock). That is a rather subtle thing not evident from the code. Add another comment? Or better do the rcu locking before calling page_lock_anon_vma and the unlocking after spin_unlock to have proper nesting of locks? We have a rather confusing rcu_read_unlock in page_lock_anon_vma.... -- 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