From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <5191B5B3.7080406@cn.fujitsu.com> Date: Tue, 14 May 2013 11:55:31 +0800 From: Tang Chen MIME-Version: 1.0 Subject: Re: [PATCH V2 1/2] mm: hotplug: implement non-movable version of get_user_pages() called get_user_pages_non_movable() References: <1360056113-14294-1-git-send-email-linfeng@cn.fujitsu.com> <1360056113-14294-2-git-send-email-linfeng@cn.fujitsu.com> <20130205120137.GG21389@suse.de> <20130206004234.GD11197@blaptop> <20130206095617.GN21389@suse.de> <5190AE4F.4000103@cn.fujitsu.com> <20130513091902.GP11497@suse.de> In-Reply-To: <20130513091902.GP11497@suse.de> Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-15; format=flowed Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Minchan Kim , Lin Feng , akpm@linux-foundation.org, bcrl@kvack.org, viro@zeniv.linux.org.uk, khlebnikov@openvz.org, walken@google.com, kamezawa.hiroyu@jp.fujitsu.com, riel@redhat.com, rientjes@google.com, isimatu.yasuaki@jp.fujitsu.com, wency@cn.fujitsu.com, laijs@cn.fujitsu.com, jiang.liu@huawei.com, zab@redhat.com, jmoyer@redhat.com, linux-mm@kvack.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Marek Szyprowski Hi Mel, On 05/13/2013 05:19 PM, Mel Gorman wrote: >> For memory hot-remove case, the aio pages are pined in memory and making >> the pages cannot be offlined, furthermore, the pages cannot be removed. >> >> IIUC, you mean implement migrate_unpin() and migrate_pin() callbacks in aio >> subsystem, and call them when hot-remove code tries to offline >> pages, right ? >> >> If so, I'm wondering where should we put this callback pointers ? >> In struct page ? >> > > No, I would expect the callbacks to be part the address space operations > which can be found via page->mapping. > Two more problems I don't quite understand. 1. For an anonymous page, it has no address_space, and no address space operation. But the aio ring problem just happened when dealing with anonymous pages. Please refer to: (https://lkml.org/lkml/2012/11/29/69) If we put the the callbacks in page->mapping->a_ops, the anonymous pages won't be able to use them. And we cannot give a default callback because the situation we are dealing with is a special situation. So where to put the callback for anonymous pages ? 2. How to find out the reason why page->count != 1 in migrate_page_move_mapping() ? In the problem we are dealing with, get_user_pages() is called to pin the pages in memory. And the pages are migratable. So we want to decrease the page->count. But get_user_pages() is not the only reason leading to page->count increased. How can I know when should decrease teh page->count or when should not ? The way I can figure out is to assign the callback pointer in get_user_pages() because it is get_user_pages() who pins the pages. Thanks. :) -- 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