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=-14.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 BFD76C07E9A for ; Tue, 13 Jul 2021 00:46:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A275B611CC for ; Tue, 13 Jul 2021 00:46:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233732AbhGMAtb (ORCPT ); Mon, 12 Jul 2021 20:49:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:44162 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233505AbhGMAta (ORCPT ); Mon, 12 Jul 2021 20:49:30 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id A083C60FDB; Tue, 13 Jul 2021 00:46:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1626137201; bh=6bUuDtl3T5ukpb4KgsVCNQhFQQRp/NYEnjIyp76CrDI=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=RTrcqMpIAK3M4VifUJz1XrGglzqn+jXET/gtby1x5QC4eq63YXZ9TE0mp5tNWwarj RyQ5mYymQ+98Fd2NTxd1eGDKSWqcMGr7UbnvMI69Oh53mQxqdX/cSFX8ppp2odDBTS gNtM1rlndrkx2r81evSvCSIpKT+gvQFVQzkHzhoKEtMSxRo/ECtK28Q5YDW4WPNr3r KpEiD3zNzb+8vWD8Soul+U7d7neyrGJtZo0yyX+hDryuYNIcHVnWuzpHe+1mPSGPfN VTneLTyAmzJsB74eCwgB0jaeYisDuEK/W6VOmoJmZ5pD4x2xeR1vvq/V99nMQP3Ue9 LgtqrqDG7bH7Q== Subject: Re: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for our internal use To: Michal Hocko Cc: Mel Gorman , Matthew Wilcox , Jaegeuk Kim , linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mm@kvack.org References: <20210706091211.GR3840@techsingularity.net> <85bb893b-0dc4-5f57-23ec-3f84814b7072@kernel.org> <20210707095706.GT3840@techsingularity.net> From: Chao Yu Message-ID: Date: Tue, 13 Jul 2021 08:46:37 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/7/12 14:53, Michal Hocko wrote: > On Sat 10-07-21 16:11:38, Chao Yu wrote: >> On 2021/7/7 17:57, Mel Gorman wrote: >>> I think it would work but it would be preferable to find out why the >>> tail page has an order set in the first place. I've looked over >> >> Agreed. >> >>> mm/page_alloc.c and mm/compaction.c a few times and did not spot where >>> set_private_page(page, 0) is missed when it should be covered by >>> clear_page_guard or del_page_from_free_list :( >> >> I didn't enable CONFIG_DEBUG_PAGEALLOC, so we will expect page private >> should be cleared by del_page_from_free_list(), but I guess it only clears >> the buddy's private field rather than original page's, so I added below >> diff and check the dmesg, it looks stall private value in original page >> will be left commonly... Let me know if I missed something? > > Page private should be cleared when the page is freed to the allocator. > Have a look at PAGE_FLAGS_CHECK_AT_FREE. Quoted from Jaegeuk's comments in [1] "Hmm, I can see it in 4.14 and 5.10 kernel. The trace is on: 30875 [ 1065.118750] c3 87 f2fs_migrate_page+0x354/0x45c 30876 [ 1065.123872] c3 87 move_to_new_page+0x70/0x30c 30877 [ 1065.128813] c3 87 migrate_pages+0x3a0/0x964 30878 [ 1065.133583] c3 87 compact_zone+0x608/0xb04 30879 [ 1065.138257] c3 87 kcompactd+0x378/0x4ec 30880 [ 1065.142664] c3 87 kthread+0x11c/0x12c 30881 [ 1065.146897] c3 87 ret_from_fork+0x10/0x18 It seems compaction_alloc() gets a free page which doesn't reset the fields?" https://lore.kernel.org/linux-f2fs-devel/YOvm2faBUjKmZI7Q@dhcp22.suse.cz/T/#m98a4a5e777f5b0e7366b367463efafd2133dd681 So problem here we met is: in f2fs_migrate_page(), newpage may has stall .private value rather than PG_private flag, which may cause f2fs will treat the page with wrong private status. > >> --- >> mm/page_alloc.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index a06bcfe6f786..1e7031ff548e 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -1029,6 +1029,7 @@ static inline void __free_one_page(struct page *page, >> unsigned long combined_pfn; >> unsigned int max_order; >> struct page *buddy; >> + struct page *orig_page = page; >> bool to_tail; >> >> max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order); >> @@ -1097,6 +1098,10 @@ static inline void __free_one_page(struct page *page, >> >> done_merging: >> set_buddy_order(page, order); >> + if (orig_page != page) { >> + if (WARN_ON_ONCE(orig_page->private)) >> + pr_info("2order:%x, origpage.private:%x", order, orig_page->private); >> + } > > Why is this expected? Buddy allocator uses page private to store order. > Whether we are merging to the freed page or coalesce it to a different The order was only set in head page, right? Since it looks __free_one_page() tries to clear page.private for every buddy with del_page_from_free_list(). If that is true, after done_merging label in __free_one_page, if original page is a tail page, we may missed to clear its page.private field? Thanks, > page is not all that important. >