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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 5F291CA9EB7 for ; Mon, 21 Oct 2019 12:58:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 40E81214B2 for ; Mon, 21 Oct 2019 12:58:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728818AbfJUM6y (ORCPT ); Mon, 21 Oct 2019 08:58:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:58546 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728081AbfJUM6x (ORCPT ); Mon, 21 Oct 2019 08:58:53 -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 433A8AC18; Mon, 21 Oct 2019 12:58:52 +0000 (UTC) Date: Mon, 21 Oct 2019 14:58:49 +0200 From: Oscar Salvador To: Michal Hocko 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 10/16] mm,hwpoison: Rework soft offline for free pages Message-ID: <20191021125842.GA11330@linux> References: <20191017142123.24245-1-osalvador@suse.de> <20191017142123.24245-11-osalvador@suse.de> <20191018120615.GM5017@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191018120615.GM5017@dhcp22.suse.cz> 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 Fri, Oct 18, 2019 at 02:06:15PM +0200, Michal Hocko wrote: > On Thu 17-10-19 16:21:17, Oscar Salvador wrote: > [...] > > +bool take_page_off_buddy(struct page *page) > > + { > > + struct zone *zone = page_zone(page); > > + unsigned long pfn = page_to_pfn(page); > > + unsigned long flags; > > + unsigned int order; > > + bool ret = false; > > + > > + spin_lock_irqsave(&zone->lock, flags); > > What prevents the page to be allocated in the meantime? Also what about > free pages on the pcp lists? Also the page could be gone by the time you > have reached here. Nothing prevents the page to be allocated in the meantime. We would just bail out and return -EBUSY to userspace. Since we do not do __anything__ to the page until we are sure we took it off, and it is completely isolated from the memory, there is no danger. Since soft-offline is kinda "best effort" mode, it is something like: "Sorry, could not poison the page, try again". Now, thinking about this a bit more, I guess we could be more clever here and call the routine that handles in-use pages if we see that the page was allocated by the time we reach take_page_off_buddy. About pcp pages, you are right. I thought that we were already handling that case, and we do, but looking closer the call to shake_page() (that among other things spills pcppages into buddy) is performed at a later stage. I think we need to adjust __get_any_page to recognize pcp pages as well. I will do some work here. Thanks for comments. -- Oscar Salvador SUSE L3