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=-17.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 A774CC433EF for ; Mon, 6 Sep 2021 12:08:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8DEE160724 for ; Mon, 6 Sep 2021 12:08:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241977AbhIFMKC (ORCPT ); Mon, 6 Sep 2021 08:10:02 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:15296 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241957AbhIFMKA (ORCPT ); Mon, 6 Sep 2021 08:10:00 -0400 Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4H36cV2wQSz8ssd; Mon, 6 Sep 2021 20:08:26 +0800 (CST) Received: from [10.174.178.100] (10.174.178.100) by dggeme703-chm.china.huawei.com (10.1.199.99) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Mon, 6 Sep 2021 20:08:53 +0800 Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page To: David Hildenbrand , CC: , , , References: <20210904091839.20270-1-linmiaohe@huawei.com> <5f7c4ac9-d17a-5af3-0326-1152cca38465@redhat.com> <2b103abc-2921-9d8a-7280-1d6b451c34f4@redhat.com> From: Miaohe Lin Message-ID: <3a9921cd-1393-f67c-1002-1320b9d1668d@huawei.com> Date: Mon, 6 Sep 2021 20:08:53 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <2b103abc-2921-9d8a-7280-1d6b451c34f4@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.100] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/9/6 20:01, David Hildenbrand wrote: > On 06.09.21 13:50, David Hildenbrand wrote: >> On 06.09.21 13:32, Miaohe Lin wrote: >>> On 2021/9/6 17:40, David Hildenbrand wrote: >>>> On 04.09.21 11:18, Miaohe Lin wrote: >>>>> If __isolate_free_page() failed, due to zone watermark check, the page is >>>>> still on the free list. But this page will be put back to free list again >>>>> via __putback_isolated_page() now. This may trigger page->flags checks in >>>>> __free_one_page() if PageReported is set. Or we will corrupt the free list >>>>> because list_add() will be called for pages already on another list. >>>>> >>>>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock") >>>>> Signed-off-by: Miaohe Lin >>>>> --- >>>>>     mm/page_isolation.c | 6 ++---- >>>>>     1 file changed, 2 insertions(+), 4 deletions(-) >>>>> >>>>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >>>>> index 9bb562d5d194..7d70d772525c 100644 >>>>> --- a/mm/page_isolation.c >>>>> +++ b/mm/page_isolation.c >>>>> @@ -93,10 +93,8 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) >>>>>                 buddy_pfn = __find_buddy_pfn(pfn, order); >>>>>                 buddy = page + (buddy_pfn - pfn); >>>>>     -            if (!is_migrate_isolate_page(buddy)) { >>>>> -                __isolate_free_page(page, order); >>>>> -                isolated_page = true; >>>>> -            } >>>>> +            if (!is_migrate_isolate_page(buddy)) >>>>> +                isolated_page = !!__isolate_free_page(page, order); >>>>>             } >>>>>         } >>>>>    >>>> >>>> Shouldn't we much rather force to ignore watermarks here and make sure __isolate_free_page() never fails? >>> >>> It seems it is not easy to force to ignore watermarks here. And it's not a problem >>> if __isolate_free_page() fails because we can do move_freepages_block() anyway. >>> What do you think? Many thanks. >> >> I'm wondering if all this complexity in this function is even required. What about something like this: (completely untested) >> >> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >> index bddf788f45bf..29ff2fcb339c 100644 >> --- a/mm/page_isolation.c >> +++ b/mm/page_isolation.c >> @@ -66,12 +66,10 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_ >>       static void unset_migratetype_isolate(struct page *page, unsigned migratetype) >>    { >> +       bool buddy_merge_possible = false; >>           struct zone *zone; >>           unsigned long flags, nr_pages; >> -       bool isolated_page = false; >>           unsigned int order; >> -       unsigned long pfn, buddy_pfn; >> -       struct page *buddy; >>              zone = page_zone(page); >>           spin_lock_irqsave(&zone->lock, flags); >> @@ -79,26 +77,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) >>                   goto out; >>              /* >> -        * Because freepage with more than pageblock_order on isolated >> -        * pageblock is restricted to merge due to freepage counting problem, >> -        * it is possible that there is free buddy page. >> -        * move_freepages_block() doesn't care of merge so we need other >> -        * approach in order to merge them. Isolation and free will make >> -        * these pages to be merged. >> +        * If our free page spans at least this whole pageblock and could >> +        * eventually get merged into an even bigger page, go via >> +        * __putback_isolated_page(), because move_freepages_block() won't >> +        * trigger merging of free pages. >>            */ >>           if (PageBuddy(page)) { >>                   order = buddy_order(page); >> -               if (order >= pageblock_order && order < MAX_ORDER - 1) { >> -                       pfn = page_to_pfn(page); >> -                       buddy_pfn = __find_buddy_pfn(pfn, order); >> -                       buddy = page + (buddy_pfn - pfn); >> - >> -                       if (pfn_valid_within(buddy_pfn) && >> -                           !is_migrate_isolate_page(buddy)) { >> -                               __isolate_free_page(page, order); >> -                               isolated_page = true; >> -                       } >> -               } >> +               if (order >= pageblock_order && order < MAX_ORDER - 1) >> +                       buddy_merge_possible = true; >>           } >>              /* >> @@ -111,12 +98,12 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) >>            * onlining - just onlined memory won't immediately be considered for >>            * allocation. >>            */ >> -       if (!isolated_page) { >> +       if (!buddy_merge_possible) { >>                   nr_pages = move_freepages_block(zone, page, migratetype, NULL); >>                   __mod_zone_freepage_state(zone, nr_pages, migratetype); >>           } >>           set_pageblock_migratetype(page, migratetype); >> -       if (isolated_page) >> +       if (buddy_merge_possible) >>                   __putback_isolated_page(page, order, migratetype); >>           zone->nr_isolate_pageblock--; >>    out: > > Okay, I just had another look -- that won't work because as you correctly said, it still is on the freelist ... > > So your fix is certainly correct :) Many thanks for your effort and suggestion. :) >