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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02FC3C43334 for ; Wed, 8 Jun 2022 14:10:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 758BB6B0071; Wed, 8 Jun 2022 10:10:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7089D6B0072; Wed, 8 Jun 2022 10:10:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5CF696B0073; Wed, 8 Jun 2022 10:10:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 4E9966B0071 for ; Wed, 8 Jun 2022 10:10:00 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id 06EAA60D08 for ; Wed, 8 Jun 2022 14:10:00 +0000 (UTC) X-FDA: 79555252560.12.6D6ABA7 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by imf29.hostedemail.com (Postfix) with ESMTP id 01995120049 for ; Wed, 8 Jun 2022 14:09:57 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4LJ8HL0qmrz8wsk; Wed, 8 Jun 2022 22:09:34 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 8 Jun 2022 22:09:52 +0800 Subject: Re: [PATCH] mm/vmscan: don't try to reclaim freed folios To: Matthew Wilcox CC: , , References: <20220527080451.48549-1-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: Date: Wed, 8 Jun 2022 22:09:52 +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: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 01995120049 Authentication-Results: imf29.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf29.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Stat-Signature: k1fttddgwpyij8pke79imp87xfk5biuq X-Rspam-User: X-HE-Tag: 1654697397-73241 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022/5/27 23:02, Matthew Wilcox wrote: > On Fri, May 27, 2022 at 04:04:51PM +0800, Miaohe Lin wrote: >> If folios were freed from under us, there's no need to reclaim them. Skip >> these folios to save lots of cpu cycles and avoid possible unnecessary >> disk IO. >> >> Signed-off-by: Miaohe Lin >> --- >> mm/vmscan.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index f7d9a683e3a7..646dd1efad32 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1556,12 +1556,18 @@ static unsigned int shrink_page_list(struct list_head *page_list, >> folio = lru_to_folio(page_list); >> list_del(&folio->lru); >> >> + nr_pages = folio_nr_pages(folio); >> + if (folio_ref_count(folio) == 1) { >> + /* folio was freed from under us. So we are done. */ >> + WARN_ON(!folio_put_testzero(folio)); > > What? No. This can absolutely happen. We have a refcount on the folio, > which means that any other thread can temporarily raise the refcount, > so this WARN_ON can trigger. Also, we don't hold the folio locked, > or an extra reference, so nr_pages is unstable because it can be split. When I reread the code, I found caller holds an extra reference to the folio when calling isolate_lru_pages(), so folio can't be split and thus nr_pages should be stable indeed? Or am I miss something again? Thanks! > >> + goto free_it; >> + } >> + >> if (!folio_trylock(folio)) >> goto keep; >> >> VM_BUG_ON_FOLIO(folio_test_active(folio), folio); >> >> - nr_pages = folio_nr_pages(folio); >> >> /* Account the number of base pages */ >> sc->nr_scanned += nr_pages; >> -- >> 2.23.0 >> >> > > . >