From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0BF8CA9EB7 for ; Mon, 21 Oct 2019 14:06:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 834682173B for ; Mon, 21 Oct 2019 14:06:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571666783; bh=ZkDcXofog1r1Cef9gtTnMlS/6SRpClDqtr0bbsWi7Tc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=mkqBAU6RmUfIY8oxJP072tmbheswsqKUSUAMhV3neoEkyAfPA66cWjtkK6aGu0d6U GsgClAYcJXQUvN0Q9SMOQXMnyIUftsR1y+Oqm7RlKpYwoGErl+2ZixqfCeCiVinpfK 1eIczRoABBTLODqrrgXYUegA4jwynpKi7GMUXG40= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729277AbfJUOGW (ORCPT ); Mon, 21 Oct 2019 10:06:22 -0400 Received: from mx2.suse.de ([195.135.220.15]:41846 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728098AbfJUOGW (ORCPT ); Mon, 21 Oct 2019 10:06:22 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 53209BD9D; Mon, 21 Oct 2019 14:06:20 +0000 (UTC) Date: Mon, 21 Oct 2019 16:06:19 +0200 From: Michal Hocko To: Oscar Salvador Cc: n-horiguchi@ah.jp.nec.com, mike.kravetz@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 11/16] mm,hwpoison: Rework soft offline for in-use pages Message-ID: <20191021140619.GQ9379@dhcp22.suse.cz> References: <20191017142123.24245-1-osalvador@suse.de> <20191017142123.24245-12-osalvador@suse.de> <20191018123901.GN5017@dhcp22.suse.cz> <20191021134846.GB11330@linux> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191021134846.GB11330@linux> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 21-10-19 15:48:48, Oscar Salvador wrote: > On Fri, Oct 18, 2019 at 02:39:01PM +0200, Michal Hocko wrote: > > > > I am sorry but I got lost in the above description and I cannot really > > make much sense from the code either. Let me try to outline the way how > > I think about this. > > > > Say we have a pfn to hwpoison. We have effectivelly three possibilities > > - page is poisoned already - done nothing to do > > - page is managed by the buddy allocator - excavate from there > > - page is in use > > > > The last category is the most interesting one. There are essentially > > three classes of pages > > - freeable > > - migrateable > > - others > > > > We cannot do really much about the last one, right? Do we mark them > > HWPoison anyway? > > We can only perform actions on LRU/Movable pages or hugetlb pages. What would prevent other pages mapped via page tables to be handled as well? > So unless the page does not fall into those areas, we do not do anything > with them. > > > Freeable should be simply marked HWPoison and freed. > > For all those migrateable, we simply do migrate and mark HWPoison. > > Now the main question is how to handle HWPoison page when it is freed > > - aka last reference is dropped. The main question is whether the last > > reference is ever dropped. If yes then the free_pages_prepare should > > never release it to the allocator (some compound destructors would have > > to special case as well, e.g. hugetlb would have to hand over to the > > allocator rather than a pool). If not then the page would be lingering > > potentially with some state bound to it (e.g. memcg charge). So I > > suspect you want the former. > > For non-hugetlb pages, we do not call put_page in the migration path, > but we do it in page_handle_poison, after the page has been flagged as > hwpoison. > Then the check in free_papes_prepare will see that the page is hwpoison > and will bail out, so the page is not released into the allocator/pcp lists. > > Hugetlb pages follow a different methodology. > They are dissolved, and then we split the higher-order page and take the > page off the buddy. > The problem is that while it is easy to hold a non-hugetlb page, > doing the same for hugetlb pages is not that easy: > > 1) we would need to hook in enqueue_hugetlb_page so the page is not enqueued > into hugetlb freelists > 2) when trying to free a hugetlb page, we would need to do as we do for gigantic > pages now, and that is breaking down the pages into order-0 pages and release > them to the buddy (so the check in free_papges_prepare would skip the > hwpoison page). > Trying to handle a higher-order hwpoison page in free_pages_prepare is > a bit complicated. I am not sure I see the problem. If you dissolve the hugetlb page then there is no hugetlb page anymore and so you make it a regular high-order page. > There is one thing I was unsure though. > Bailing out at the beginning of free_pages_prepare if the page is hwpoison > means that the calls to > > - __memcg_kmem_uncharge > - page_cpupid_reset_last > - reset_page_owner > - ... > > will not be performed. > I thought this is right because the page is not really "free", it is just unusable, > so.. it should be still charged to the memcg? If the page is free then it shouldn't pin the memcg or any other state. -- Michal Hocko SUSE Labs