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=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 0787FC433E1 for ; Thu, 20 Aug 2020 06:18:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C9CA72075E for ; Thu, 20 Aug 2020 06:18:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C9CA72075E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 564CD6B00A1; Thu, 20 Aug 2020 02:18:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 513C96B00A2; Thu, 20 Aug 2020 02:18:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3DDE68D0005; Thu, 20 Aug 2020 02:18:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0047.hostedemail.com [216.40.44.47]) by kanga.kvack.org (Postfix) with ESMTP id 287486B00A1 for ; Thu, 20 Aug 2020 02:18:34 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id CF621248F for ; Thu, 20 Aug 2020 06:18:33 +0000 (UTC) X-FDA: 77169942906.09.gun13_000793b2702e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin09.hostedemail.com (Postfix) with ESMTP id A2928180AD811 for ; Thu, 20 Aug 2020 06:18:33 +0000 (UTC) X-HE-Tag: gun13_000793b2702e X-Filterd-Recvd-Size: 4710 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 06:18:33 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id C6C16B585; Thu, 20 Aug 2020 06:18:58 +0000 (UTC) Date: Thu, 20 Aug 2020 08:18:27 +0200 From: Michal Hocko To: Yu Zhao Cc: Andrew Morton , Alexander Duyck , Huang Ying , David Hildenbrand , Yang Shi , Qian Cai , Mel Gorman , Nicholas Piggin , =?iso-8859-1?B?Suly9G1l?= Glisse , Hugh Dickins , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim Subject: Re: [PATCH v2 3/3] mm: remove superfluous __ClearPageWaiters() Message-ID: <20200820061652.GX5422@dhcp22.suse.cz> References: <20200818184704.3625199-1-yuzhao@google.com> <20200818184704.3625199-3-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200818184704.3625199-3-yuzhao@google.com> X-Rspamd-Queue-Id: A2928180AD811 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 Tue 18-08-20 12:47:04, Yu Zhao wrote: > Presumably __ClearPageWaiters() was added to follow the previously > removed __ClearPageActive() pattern. I do not think so. Please have a look at 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit") and a discussion when the patch has been proposed. Sorry I do not have a link handy but I do remember that the handling was quite subtle. > Only flags that are in PAGE_FLAGS_CHECK_AT_FREE needs to be properly > cleared because otherwise we think there may be some kind of leak. > PG_waiters is not one of those flags and leaving the clearing to > PAGE_FLAGS_CHECK_AT_PREP is more appropriate. What is the point of this patch in the first place? Page waiters is quite subtle and I wouldn't touch it without having a very good reason. > Signed-off-by: Yu Zhao > --- > include/linux/page-flags.h | 2 +- > mm/filemap.c | 2 ++ > mm/memremap.c | 2 -- > mm/swap.c | 3 --- > 4 files changed, 3 insertions(+), 6 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 6be1aa559b1e..dba80a2bdfba 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -318,7 +318,7 @@ static inline int TestClearPage##uname(struct page *page) { return 0; } > TESTSETFLAG_FALSE(uname) TESTCLEARFLAG_FALSE(uname) > > __PAGEFLAG(Locked, locked, PF_NO_TAIL) > -PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) > +PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) > PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL) > PAGEFLAG(Referenced, referenced, PF_HEAD) > TESTCLEARFLAG(Referenced, referenced, PF_HEAD) > diff --git a/mm/filemap.c b/mm/filemap.c > index 1aaea26556cc..75240c7ef73f 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1079,6 +1079,8 @@ static void wake_up_page_bit(struct page *page, int bit_nr) > * other pages on it. > * > * That's okay, it's a rare case. The next waker will clear it. > + * Otherwise the bit will be cleared by PAGE_FLAGS_CHECK_AT_PREP > + * when the page is being freed. > */ > } > spin_unlock_irqrestore(&q->lock, flags); > diff --git a/mm/memremap.c b/mm/memremap.c > index 3a06eb91cb59..a9d02ffaf9e3 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -451,8 +451,6 @@ void free_devmap_managed_page(struct page *page) > return; > } > > - __ClearPageWaiters(page); > - > mem_cgroup_uncharge(page); > > /* > diff --git a/mm/swap.c b/mm/swap.c > index 999a84dbe12c..40bf20a75278 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -90,7 +90,6 @@ static void __page_cache_release(struct page *page) > del_page_from_lru_list(page, lruvec, page_off_lru(page)); > spin_unlock_irqrestore(&pgdat->lru_lock, flags); > } > - __ClearPageWaiters(page); > } > > static void __put_single_page(struct page *page) > @@ -900,8 +899,6 @@ void release_pages(struct page **pages, int nr) > del_page_from_lru_list(page, lruvec, page_off_lru(page)); > } > > - __ClearPageWaiters(page); > - > list_add(&page->lru, &pages_to_free); > } > if (locked_pgdat) > -- > 2.28.0.220.ged08abb693-goog > -- Michal Hocko SUSE Labs