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 4DCD5CA9EB7 for ; Mon, 21 Oct 2019 15:42:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2371D20873 for ; Mon, 21 Oct 2019 15:42:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571672523; bh=pe6wXcO3jDuMibDCNI6MAcNzt7uASgB+Lk3Qh7R/3XA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Cu1g8oW8PtuliI+e7BvLChl3I5OqFFJq/v6h1ax53Cci8wWmVfxBRzGjFcvWhGt9+ tFmVBigTDnsyDLtzkbFfp4h2vICyQ+M5DKifgiVANzUNuhpZFABRcoenRY8Qxv6xCh u2kiTTDg/iHNhfXZnFQp5Y8XyADoGNBpsbXj/N6g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729685AbfJUPmB (ORCPT ); Mon, 21 Oct 2019 11:42:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:49392 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727680AbfJUPmA (ORCPT ); Mon, 21 Oct 2019 11:42:00 -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 183E0B392; Mon, 21 Oct 2019 15:41:59 +0000 (UTC) Date: Mon, 21 Oct 2019 17:41:58 +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 10/16] mm,hwpoison: Rework soft offline for free pages Message-ID: <20191021154158.GV9379@dhcp22.suse.cz> References: <20191017142123.24245-1-osalvador@suse.de> <20191017142123.24245-11-osalvador@suse.de> <20191018120615.GM5017@dhcp22.suse.cz> <20191021125842.GA11330@linux> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191021125842.GA11330@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 14:58:49, Oscar Salvador wrote: > 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. Wouldn't it be better to simply check the PageBuddy state after the lock has been taken? > Since soft-offline is kinda "best effort" mode, it is something like: > "Sorry, could not poison the page, try again". Well, I would disagree here. While madvise is indeed a best effort operation please keep in mind that the sole purpose of this interface is to allow real MCE behavior. And that operation should better try _really_ hard to make sure we try to recover as gracefully as possible. > 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. Yeah, pcp pages are PITA. We cannot really recognize them now. Dropping all pcp pages is certainly a way to go but we need to mark the page before that happens. -- Michal Hocko SUSE Labs