From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 30 Nov 2006 20:12:32 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC][PATCH 0/1] Node-based reclaim/migration Message-Id: <20061130201232.7d5f5578.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <6599ad830611300245s5c0f40bdu4231832930e9c023@mail.gmail.com> References: <20061129030655.941148000@menage.corp.google.com> <20061130093105.d872c49d.kamezawa.hiroyu@jp.fujitsu.com> <6599ad830611291631hd6d3e52y971c35708004db00@mail.gmail.com> <6599ad830611300245s5c0f40bdu4231832930e9c023@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Paul Menage Cc: clameter@sgi.com, linux-mm@kvack.org, akpm@osdl.org List-ID: On Thu, 30 Nov 2006 02:45:51 -0800 "Paul Menage" wrote: > On 11/29/06, Christoph Lameter wrote: > > > > You do not have a problem as long as you hold a mmap_sem lock on any of > > the vmas in which the page appears. Kame and I discussed several > > approached on how to avoid the issue in the past but so far there was no > > need to resolve the issue. > > > > It sounds like this would be useful for memory hot-unplug too, though. > A problem worth solving? > It's not solved just because 'there is no user'. If you'll fix it, I welcome it. > Why isn't page_lock_anon_vma() safe to use in this case? Because after > we've established migration ptes, page_mapped() will be false and so > page_lock_anon_vma() will return NULL? page_lock_anon_vma() will return NULL because mapcount is 0. We have to guarantee that we can trust anon_vma(from page->mapping0 even if page->mapcount is 0.maybe there is several ways. > How does kswapd do this safely? > kswapd doesn't touches page->mapping after page_mapcount() goes down to 0. > Possible approach (apologies if you've already considered and rejected this): > As you pointed out, there will be several approaches. I think one of the biggest concern will be performance impact. And this will touch objrmap core, it is good to start discussion with a patch. -Kame > -- 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