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=-24.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 920E6C433E0 for ; Wed, 10 Feb 2021 20:15:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5AC6D64E35 for ; Wed, 10 Feb 2021 20:15:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232692AbhBJUPL (ORCPT ); Wed, 10 Feb 2021 15:15:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59508 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232292AbhBJUPC (ORCPT ); Wed, 10 Feb 2021 15:15:02 -0500 Received: from mail-ot1-x32f.google.com (mail-ot1-x32f.google.com [IPv6:2607:f8b0:4864:20::32f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 279B4C06178A for ; Wed, 10 Feb 2021 12:14:22 -0800 (PST) Received: by mail-ot1-x32f.google.com with SMTP id r21so3006949otk.13 for ; Wed, 10 Feb 2021 12:14:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=vfeESgYKQlcCkrabdohSi++msd7243Sr3Sj5ghNPOJg=; b=t7G6OrEaijpiuFRWJhuXuitJBqvd9NrzYyjbNd+Rp2UQn+90DaNMWI0IfVtgeNR2cN O03eUDDPzVkhymdnbEnkyyGwLu4j8ieOQ5NESxn6Tn9wKyH6RxBXfsv2+QjebyfGFkeZ EN0vGaQVykHn++sUGG/3U9MqlxCdBQZKpoHUeGmj/IE7HBqgB/xW8ZsczS00igSO0iXq uV9937SVNibdWaY3xv7tPK2bQ19R0abLVLlgXEK7A3ej1gkZPMvie9KImXpDEQvVkN0l oIOJs0MI09qKtfqmWDzczyrVBir0PNQX+jwff99Z5zPhO4zk6fCbNLacuzGtYyudbVIk agRQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version; bh=vfeESgYKQlcCkrabdohSi++msd7243Sr3Sj5ghNPOJg=; b=TLsrVANAuvjRZmHN848w4OxliIdMhBBXjfivbF017Zph/+Cn1zWBHiu8ximUyNgm7U NG7bdEd8gMpc3JlWI46TtuZCHIA45r+i5LLbqwnZf7kuV+o6e25ABA98OvOxKTi/fgqC Xhnr4e6Op71MhtDsXntz7x2k/+RXrmV4r0IsfS4YkOZ1vOFLzuirspTnd9jeF2vsGBjj cMX/ljhCAWe5sZ9LfLRqauZRyysT5Id/1bXpm9zwsp50i7w6hgjB7fs5KoP9bPLnvvz3 /w1m6LgV97tMjXiblZ7irhp3oJkOda0Wb4ikP5m6tXL/tmlKAAjcsNZ7dxXkDiN2AwT4 RenQ== X-Gm-Message-State: AOAM5339fp/GFtAvG8m5CN/aCiK6HqQj09EPqZtCvzj95HTkGcQypvC0 wGWnFCGBMJqQC2/xgqbOiddFYA== X-Google-Smtp-Source: ABdhPJwBEhXL7qKC9+v6FuAu9WRCWRCOCW7Xnd7BVDsdozSaCKysy6R7WVRrxE9VkZL/a8cprbWaEA== X-Received: by 2002:a05:6830:90a:: with SMTP id v10mr3468335ott.364.1612988061207; Wed, 10 Feb 2021 12:14:21 -0800 (PST) Received: from eggly.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id c20sm651140oiw.18.2021.02.10.12.14.19 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Wed, 10 Feb 2021 12:14:20 -0800 (PST) Date: Wed, 10 Feb 2021 12:14:08 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Johannes Weiner cc: Hugh Dickins , Andrew Morton , Michal Hocko , Shakeel Butt , Roman Gushchin , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v2] mm: page-writeback: simplify memcg handling in test_clear_page_writeback() In-Reply-To: Message-ID: References: <20210209214543.112655-1-hannes@cmpxchg.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 10 Feb 2021, Johannes Weiner wrote: > On Wed, Feb 10, 2021 at 08:22:00AM -0800, Hugh Dickins wrote: > > On Tue, 9 Feb 2021, Hugh Dickins wrote: > > > On Tue, 9 Feb 2021, Johannes Weiner wrote: > > > > > > > Page writeback doesn't hold a page reference, which allows truncate to > > > > free a page the second PageWriteback is cleared. This used to require > > > > special attention in test_clear_page_writeback(), where we had to be > > > > careful not to rely on the unstable page->memcg binding and look up > > > > all the necessary information before clearing the writeback flag. > > > > > > > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > > > > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > > > > explicit reference on the page, and this dance is no longer needed. > > > > > > > > Use unlock_page_memcg() and dec_lruvec_page_stat() directly. > > > > > > s/stat()/state()/ > > > > > > This is a nice cleanup: I hadn't seen that connection at all. > > > > > > But I think you should take it further: > > > __unlock_page_memcg() can then be static in mm/memcontrol.c, > > > and its declarations deleted from include/linux/memcontrol.h? > > > > And further: void lock_page_memcg(page), not returning memcg. > > You're right on all counts! > > > > And further: delete __dec_lruvec_state() and dec_lruvec_state() > > > from include/linux/vmstat.h - unless you feel that every "inc" > > > ought to be matched by a "dec", even when unused. > > Hey look, there isn't a user for the __inc, either :) There is one for > inc, but I don't insist on having symmetry there. > > > > > Signed-off-by: Johannes Weiner > > > > > > Acked-by: Hugh Dickins > > Thanks for the review and good feedback. > > How about this v2? Yes, even nicer, thank you: SetPatchDoubleAcked. > > --- > > From 5bcc0f468460aa2670c40318bb657e8b08ef96d5 Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Tue, 9 Feb 2021 16:22:42 -0500 > Subject: [PATCH] mm: page-writeback: simplify memcg handling in > test_clear_page_writeback() > > Page writeback doesn't hold a page reference, which allows truncate to > free a page the second PageWriteback is cleared. This used to require > special attention in test_clear_page_writeback(), where we had to be > careful not to rely on the unstable page->memcg binding and look up > all the necessary information before clearing the writeback flag. > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > explicit reference on the page, and this dance is no longer needed. > > Use unlock_page_memcg() and dec_lruvec_page_state() directly. > > This removes the last user of the lock_page_memcg() return value, > change it to void. Touch up the comments in there as well. This also > removes the last extern user of __unlock_page_memcg(), make it > static. Further, it removes the last user of dec_lruvec_state(), > delete it, along with a few other unused helpers. > > Signed-off-by: Johannes Weiner > Acked-by: Hugh Dickins > Reviewed-by: Shakeel Butt > --- > include/linux/memcontrol.h | 10 ++-------- > include/linux/vmstat.h | 24 +++--------------------- > mm/memcontrol.c | 36 +++++++++++------------------------- > mm/page-writeback.c | 9 +++------ > 4 files changed, 19 insertions(+), 60 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index a44b2d51aecc..b17053af3287 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -874,8 +874,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg); > extern bool cgroup_memory_noswap; > #endif > > -struct mem_cgroup *lock_page_memcg(struct page *page); > -void __unlock_page_memcg(struct mem_cgroup *memcg); > +void lock_page_memcg(struct page *page); > void unlock_page_memcg(struct page *page); > > void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val); > @@ -1269,12 +1268,7 @@ mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) > { > } > > -static inline struct mem_cgroup *lock_page_memcg(struct page *page) > -{ > - return NULL; > -} > - > -static inline void __unlock_page_memcg(struct mem_cgroup *memcg) > +static inline void lock_page_memcg(struct page *page) > { > } > > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h > index 506d625163a1..3299cd69e4ca 100644 > --- a/include/linux/vmstat.h > +++ b/include/linux/vmstat.h > @@ -512,16 +512,10 @@ static inline void mod_lruvec_page_state(struct page *page, > > #endif /* CONFIG_MEMCG */ > > -static inline void __inc_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - __mod_lruvec_state(lruvec, idx, 1); > -} > - > -static inline void __dec_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > +static inline void inc_lruvec_state(struct lruvec *lruvec, > + enum node_stat_item idx) > { > - __mod_lruvec_state(lruvec, idx, -1); > + mod_lruvec_state(lruvec, idx, 1); > } > > static inline void __inc_lruvec_page_state(struct page *page, > @@ -536,18 +530,6 @@ static inline void __dec_lruvec_page_state(struct page *page, > __mod_lruvec_page_state(page, idx, -1); > } > > -static inline void inc_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - mod_lruvec_state(lruvec, idx, 1); > -} > - > -static inline void dec_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - mod_lruvec_state(lruvec, idx, -1); > -} > - > static inline void inc_lruvec_page_state(struct page *page, > enum node_stat_item idx) > { > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 9e455815fb7a..e29d3d64c27e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2124,11 +2124,10 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg) > * This function protects unlocked LRU pages from being moved to > * another cgroup. > * > - * It ensures lifetime of the returned memcg. Caller is responsible > - * for the lifetime of the page; __unlock_page_memcg() is available > - * when @page might get freed inside the locked section. > + * It ensures lifetime of the locked memcg. Caller is responsible > + * for the lifetime of the page. > */ > -struct mem_cgroup *lock_page_memcg(struct page *page) > +void lock_page_memcg(struct page *page) > { > struct page *head = compound_head(page); /* rmap on tail pages */ > struct mem_cgroup *memcg; > @@ -2138,21 +2137,15 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > * The RCU lock is held throughout the transaction. The fast > * path can get away without acquiring the memcg->move_lock > * because page moving starts with an RCU grace period. > - * > - * The RCU lock also protects the memcg from being freed when > - * the page state that is going to change is the only thing > - * preventing the page itself from being freed. E.g. writeback > - * doesn't hold a page reference and relies on PG_writeback to > - * keep off truncation, migration and so forth. > */ > rcu_read_lock(); > > if (mem_cgroup_disabled()) > - return NULL; > + return; > again: > memcg = page_memcg(head); > if (unlikely(!memcg)) > - return NULL; > + return; > > #ifdef CONFIG_PROVE_LOCKING > local_irq_save(flags); > @@ -2161,7 +2154,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > #endif > > if (atomic_read(&memcg->moving_account) <= 0) > - return memcg; > + return; > > spin_lock_irqsave(&memcg->move_lock, flags); > if (memcg != page_memcg(head)) { > @@ -2170,24 +2163,17 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > } > > /* > - * When charge migration first begins, we can have locked and > - * unlocked page stat updates happening concurrently. Track > - * the task who has the lock for unlock_page_memcg(). > + * When charge migration first begins, we can have multiple > + * critical sections holding the fast-path RCU lock and one > + * holding the slowpath move_lock. Track the task who has the > + * move_lock for unlock_page_memcg(). > */ > memcg->move_lock_task = current; > memcg->move_lock_flags = flags; > - > - return memcg; > } > EXPORT_SYMBOL(lock_page_memcg); > > -/** > - * __unlock_page_memcg - unlock and unpin a memcg > - * @memcg: the memcg > - * > - * Unlock and unpin a memcg returned by lock_page_memcg(). > - */ > -void __unlock_page_memcg(struct mem_cgroup *memcg) > +static void __unlock_page_memcg(struct mem_cgroup *memcg) > { > if (memcg && memcg->move_lock_task == current) { > unsigned long flags = memcg->move_lock_flags; > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index eb34d204d4ee..f6c2c3165d4d 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -2722,12 +2722,9 @@ EXPORT_SYMBOL(clear_page_dirty_for_io); > int test_clear_page_writeback(struct page *page) > { > struct address_space *mapping = page_mapping(page); > - struct mem_cgroup *memcg; > - struct lruvec *lruvec; > int ret; > > - memcg = lock_page_memcg(page); > - lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page)); > + lock_page_memcg(page); > if (mapping && mapping_use_writeback_tags(mapping)) { > struct inode *inode = mapping->host; > struct backing_dev_info *bdi = inode_to_bdi(inode); > @@ -2755,11 +2752,11 @@ int test_clear_page_writeback(struct page *page) > ret = TestClearPageWriteback(page); > } > if (ret) { > - dec_lruvec_state(lruvec, NR_WRITEBACK); > + dec_lruvec_page_state(page, NR_WRITEBACK); > dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); > inc_node_page_state(page, NR_WRITTEN); > } > - __unlock_page_memcg(memcg); > + unlock_page_memcg(page); > return ret; > } > > -- > 2.30.0 > > 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=-24.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 6FC15C433E0 for ; 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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id c20sm651140oiw.18.2021.02.10.12.14.19 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Wed, 10 Feb 2021 12:14:20 -0800 (PST) Date: Wed, 10 Feb 2021 12:14:08 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Johannes Weiner cc: Hugh Dickins , Andrew Morton , Michal Hocko , Shakeel Butt , Roman Gushchin , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v2] mm: page-writeback: simplify memcg handling in test_clear_page_writeback() In-Reply-To: Message-ID: References: <20210209214543.112655-1-hannes@cmpxchg.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 07194C000C4B X-Stat-Signature: hbnxmpo1ykjop6fiij6jnexshqdi6jh3 Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf03; identity=mailfrom; envelope-from=""; helo=mail-ot1-f51.google.com; client-ip=209.85.210.51 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612988060-535405 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 Wed, 10 Feb 2021, Johannes Weiner wrote: > On Wed, Feb 10, 2021 at 08:22:00AM -0800, Hugh Dickins wrote: > > On Tue, 9 Feb 2021, Hugh Dickins wrote: > > > On Tue, 9 Feb 2021, Johannes Weiner wrote: > > > > > > > Page writeback doesn't hold a page reference, which allows truncate to > > > > free a page the second PageWriteback is cleared. This used to require > > > > special attention in test_clear_page_writeback(), where we had to be > > > > careful not to rely on the unstable page->memcg binding and look up > > > > all the necessary information before clearing the writeback flag. > > > > > > > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > > > > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > > > > explicit reference on the page, and this dance is no longer needed. > > > > > > > > Use unlock_page_memcg() and dec_lruvec_page_stat() directly. > > > > > > s/stat()/state()/ > > > > > > This is a nice cleanup: I hadn't seen that connection at all. > > > > > > But I think you should take it further: > > > __unlock_page_memcg() can then be static in mm/memcontrol.c, > > > and its declarations deleted from include/linux/memcontrol.h? > > > > And further: void lock_page_memcg(page), not returning memcg. > > You're right on all counts! > > > > And further: delete __dec_lruvec_state() and dec_lruvec_state() > > > from include/linux/vmstat.h - unless you feel that every "inc" > > > ought to be matched by a "dec", even when unused. > > Hey look, there isn't a user for the __inc, either :) There is one for > inc, but I don't insist on having symmetry there. > > > > > Signed-off-by: Johannes Weiner > > > > > > Acked-by: Hugh Dickins > > Thanks for the review and good feedback. > > How about this v2? Yes, even nicer, thank you: SetPatchDoubleAcked. > > --- > > From 5bcc0f468460aa2670c40318bb657e8b08ef96d5 Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Tue, 9 Feb 2021 16:22:42 -0500 > Subject: [PATCH] mm: page-writeback: simplify memcg handling in > test_clear_page_writeback() > > Page writeback doesn't hold a page reference, which allows truncate to > free a page the second PageWriteback is cleared. This used to require > special attention in test_clear_page_writeback(), where we had to be > careful not to rely on the unstable page->memcg binding and look up > all the necessary information before clearing the writeback flag. > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > explicit reference on the page, and this dance is no longer needed. > > Use unlock_page_memcg() and dec_lruvec_page_state() directly. > > This removes the last user of the lock_page_memcg() return value, > change it to void. Touch up the comments in there as well. This also > removes the last extern user of __unlock_page_memcg(), make it > static. Further, it removes the last user of dec_lruvec_state(), > delete it, along with a few other unused helpers. > > Signed-off-by: Johannes Weiner > Acked-by: Hugh Dickins > Reviewed-by: Shakeel Butt > --- > include/linux/memcontrol.h | 10 ++-------- > include/linux/vmstat.h | 24 +++--------------------- > mm/memcontrol.c | 36 +++++++++++------------------------- > mm/page-writeback.c | 9 +++------ > 4 files changed, 19 insertions(+), 60 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index a44b2d51aecc..b17053af3287 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -874,8 +874,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg); > extern bool cgroup_memory_noswap; > #endif > > -struct mem_cgroup *lock_page_memcg(struct page *page); > -void __unlock_page_memcg(struct mem_cgroup *memcg); > +void lock_page_memcg(struct page *page); > void unlock_page_memcg(struct page *page); > > void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val); > @@ -1269,12 +1268,7 @@ mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) > { > } > > -static inline struct mem_cgroup *lock_page_memcg(struct page *page) > -{ > - return NULL; > -} > - > -static inline void __unlock_page_memcg(struct mem_cgroup *memcg) > +static inline void lock_page_memcg(struct page *page) > { > } > > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h > index 506d625163a1..3299cd69e4ca 100644 > --- a/include/linux/vmstat.h > +++ b/include/linux/vmstat.h > @@ -512,16 +512,10 @@ static inline void mod_lruvec_page_state(struct page *page, > > #endif /* CONFIG_MEMCG */ > > -static inline void __inc_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - __mod_lruvec_state(lruvec, idx, 1); > -} > - > -static inline void __dec_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > +static inline void inc_lruvec_state(struct lruvec *lruvec, > + enum node_stat_item idx) > { > - __mod_lruvec_state(lruvec, idx, -1); > + mod_lruvec_state(lruvec, idx, 1); > } > > static inline void __inc_lruvec_page_state(struct page *page, > @@ -536,18 +530,6 @@ static inline void __dec_lruvec_page_state(struct page *page, > __mod_lruvec_page_state(page, idx, -1); > } > > -static inline void inc_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - mod_lruvec_state(lruvec, idx, 1); > -} > - > -static inline void dec_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - mod_lruvec_state(lruvec, idx, -1); > -} > - > static inline void inc_lruvec_page_state(struct page *page, > enum node_stat_item idx) > { > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 9e455815fb7a..e29d3d64c27e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2124,11 +2124,10 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg) > * This function protects unlocked LRU pages from being moved to > * another cgroup. > * > - * It ensures lifetime of the returned memcg. Caller is responsible > - * for the lifetime of the page; __unlock_page_memcg() is available > - * when @page might get freed inside the locked section. > + * It ensures lifetime of the locked memcg. Caller is responsible > + * for the lifetime of the page. > */ > -struct mem_cgroup *lock_page_memcg(struct page *page) > +void lock_page_memcg(struct page *page) > { > struct page *head = compound_head(page); /* rmap on tail pages */ > struct mem_cgroup *memcg; > @@ -2138,21 +2137,15 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > * The RCU lock is held throughout the transaction. The fast > * path can get away without acquiring the memcg->move_lock > * because page moving starts with an RCU grace period. > - * > - * The RCU lock also protects the memcg from being freed when > - * the page state that is going to change is the only thing > - * preventing the page itself from being freed. E.g. writeback > - * doesn't hold a page reference and relies on PG_writeback to > - * keep off truncation, migration and so forth. > */ > rcu_read_lock(); > > if (mem_cgroup_disabled()) > - return NULL; > + return; > again: > memcg = page_memcg(head); > if (unlikely(!memcg)) > - return NULL; > + return; > > #ifdef CONFIG_PROVE_LOCKING > local_irq_save(flags); > @@ -2161,7 +2154,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > #endif > > if (atomic_read(&memcg->moving_account) <= 0) > - return memcg; > + return; > > spin_lock_irqsave(&memcg->move_lock, flags); > if (memcg != page_memcg(head)) { > @@ -2170,24 +2163,17 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > } > > /* > - * When charge migration first begins, we can have locked and > - * unlocked page stat updates happening concurrently. Track > - * the task who has the lock for unlock_page_memcg(). > + * When charge migration first begins, we can have multiple > + * critical sections holding the fast-path RCU lock and one > + * holding the slowpath move_lock. Track the task who has the > + * move_lock for unlock_page_memcg(). > */ > memcg->move_lock_task = current; > memcg->move_lock_flags = flags; > - > - return memcg; > } > EXPORT_SYMBOL(lock_page_memcg); > > -/** > - * __unlock_page_memcg - unlock and unpin a memcg > - * @memcg: the memcg > - * > - * Unlock and unpin a memcg returned by lock_page_memcg(). > - */ > -void __unlock_page_memcg(struct mem_cgroup *memcg) > +static void __unlock_page_memcg(struct mem_cgroup *memcg) > { > if (memcg && memcg->move_lock_task == current) { > unsigned long flags = memcg->move_lock_flags; > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index eb34d204d4ee..f6c2c3165d4d 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -2722,12 +2722,9 @@ EXPORT_SYMBOL(clear_page_dirty_for_io); > int test_clear_page_writeback(struct page *page) > { > struct address_space *mapping = page_mapping(page); > - struct mem_cgroup *memcg; > - struct lruvec *lruvec; > int ret; > > - memcg = lock_page_memcg(page); > - lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page)); > + lock_page_memcg(page); > if (mapping && mapping_use_writeback_tags(mapping)) { > struct inode *inode = mapping->host; > struct backing_dev_info *bdi = inode_to_bdi(inode); > @@ -2755,11 +2752,11 @@ int test_clear_page_writeback(struct page *page) > ret = TestClearPageWriteback(page); > } > if (ret) { > - dec_lruvec_state(lruvec, NR_WRITEBACK); > + dec_lruvec_page_state(page, NR_WRITEBACK); > dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); > inc_node_page_state(page, NR_WRITTEN); > } > - __unlock_page_memcg(memcg); > + unlock_page_memcg(page); > return ret; > } > > -- > 2.30.0 > > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hugh Dickins Subject: Re: [PATCH v2] mm: page-writeback: simplify memcg handling in test_clear_page_writeback() Date: Wed, 10 Feb 2021 12:14:08 -0800 (PST) Message-ID: References: <20210209214543.112655-1-hannes@cmpxchg.org> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=vfeESgYKQlcCkrabdohSi++msd7243Sr3Sj5ghNPOJg=; b=t7G6OrEaijpiuFRWJhuXuitJBqvd9NrzYyjbNd+Rp2UQn+90DaNMWI0IfVtgeNR2cN O03eUDDPzVkhymdnbEnkyyGwLu4j8ieOQ5NESxn6Tn9wKyH6RxBXfsv2+QjebyfGFkeZ EN0vGaQVykHn++sUGG/3U9MqlxCdBQZKpoHUeGmj/IE7HBqgB/xW8ZsczS00igSO0iXq uV9937SVNibdWaY3xv7tPK2bQ19R0abLVLlgXEK7A3ej1gkZPMvie9KImXpDEQvVkN0l oIOJs0MI09qKtfqmWDzczyrVBir0PNQX+jwff99Z5zPhO4zk6fCbNLacuzGtYyudbVIk agRQ== In-Reply-To: List-ID: Content-Type: TEXT/PLAIN; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Johannes Weiner Cc: Hugh Dickins , Andrew Morton , Michal Hocko , Shakeel Butt , Roman Gushchin , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org On Wed, 10 Feb 2021, Johannes Weiner wrote: > On Wed, Feb 10, 2021 at 08:22:00AM -0800, Hugh Dickins wrote: > > On Tue, 9 Feb 2021, Hugh Dickins wrote: > > > On Tue, 9 Feb 2021, Johannes Weiner wrote: > > > > > > > Page writeback doesn't hold a page reference, which allows truncate to > > > > free a page the second PageWriteback is cleared. This used to require > > > > special attention in test_clear_page_writeback(), where we had to be > > > > careful not to rely on the unstable page->memcg binding and look up > > > > all the necessary information before clearing the writeback flag. > > > > > > > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > > > > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > > > > explicit reference on the page, and this dance is no longer needed. > > > > > > > > Use unlock_page_memcg() and dec_lruvec_page_stat() directly. > > > > > > s/stat()/state()/ > > > > > > This is a nice cleanup: I hadn't seen that connection at all. > > > > > > But I think you should take it further: > > > __unlock_page_memcg() can then be static in mm/memcontrol.c, > > > and its declarations deleted from include/linux/memcontrol.h? > > > > And further: void lock_page_memcg(page), not returning memcg. > > You're right on all counts! > > > > And further: delete __dec_lruvec_state() and dec_lruvec_state() > > > from include/linux/vmstat.h - unless you feel that every "inc" > > > ought to be matched by a "dec", even when unused. > > Hey look, there isn't a user for the __inc, either :) There is one for > inc, but I don't insist on having symmetry there. > > > > > Signed-off-by: Johannes Weiner > > > > > > Acked-by: Hugh Dickins > > Thanks for the review and good feedback. > > How about this v2? Yes, even nicer, thank you: SetPatchDoubleAcked. > > --- > > From 5bcc0f468460aa2670c40318bb657e8b08ef96d5 Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Tue, 9 Feb 2021 16:22:42 -0500 > Subject: [PATCH] mm: page-writeback: simplify memcg handling in > test_clear_page_writeback() > > Page writeback doesn't hold a page reference, which allows truncate to > free a page the second PageWriteback is cleared. This used to require > special attention in test_clear_page_writeback(), where we had to be > careful not to rely on the unstable page->memcg binding and look up > all the necessary information before clearing the writeback flag. > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > explicit reference on the page, and this dance is no longer needed. > > Use unlock_page_memcg() and dec_lruvec_page_state() directly. > > This removes the last user of the lock_page_memcg() return value, > change it to void. Touch up the comments in there as well. This also > removes the last extern user of __unlock_page_memcg(), make it > static. Further, it removes the last user of dec_lruvec_state(), > delete it, along with a few other unused helpers. > > Signed-off-by: Johannes Weiner > Acked-by: Hugh Dickins > Reviewed-by: Shakeel Butt > --- > include/linux/memcontrol.h | 10 ++-------- > include/linux/vmstat.h | 24 +++--------------------- > mm/memcontrol.c | 36 +++++++++++------------------------- > mm/page-writeback.c | 9 +++------ > 4 files changed, 19 insertions(+), 60 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index a44b2d51aecc..b17053af3287 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -874,8 +874,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg); > extern bool cgroup_memory_noswap; > #endif > > -struct mem_cgroup *lock_page_memcg(struct page *page); > -void __unlock_page_memcg(struct mem_cgroup *memcg); > +void lock_page_memcg(struct page *page); > void unlock_page_memcg(struct page *page); > > void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val); > @@ -1269,12 +1268,7 @@ mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) > { > } > > -static inline struct mem_cgroup *lock_page_memcg(struct page *page) > -{ > - return NULL; > -} > - > -static inline void __unlock_page_memcg(struct mem_cgroup *memcg) > +static inline void lock_page_memcg(struct page *page) > { > } > > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h > index 506d625163a1..3299cd69e4ca 100644 > --- a/include/linux/vmstat.h > +++ b/include/linux/vmstat.h > @@ -512,16 +512,10 @@ static inline void mod_lruvec_page_state(struct page *page, > > #endif /* CONFIG_MEMCG */ > > -static inline void __inc_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - __mod_lruvec_state(lruvec, idx, 1); > -} > - > -static inline void __dec_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > +static inline void inc_lruvec_state(struct lruvec *lruvec, > + enum node_stat_item idx) > { > - __mod_lruvec_state(lruvec, idx, -1); > + mod_lruvec_state(lruvec, idx, 1); > } > > static inline void __inc_lruvec_page_state(struct page *page, > @@ -536,18 +530,6 @@ static inline void __dec_lruvec_page_state(struct page *page, > __mod_lruvec_page_state(page, idx, -1); > } > > -static inline void inc_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - mod_lruvec_state(lruvec, idx, 1); > -} > - > -static inline void dec_lruvec_state(struct lruvec *lruvec, > - enum node_stat_item idx) > -{ > - mod_lruvec_state(lruvec, idx, -1); > -} > - > static inline void inc_lruvec_page_state(struct page *page, > enum node_stat_item idx) > { > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 9e455815fb7a..e29d3d64c27e 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2124,11 +2124,10 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg) > * This function protects unlocked LRU pages from being moved to > * another cgroup. > * > - * It ensures lifetime of the returned memcg. Caller is responsible > - * for the lifetime of the page; __unlock_page_memcg() is available > - * when @page might get freed inside the locked section. > + * It ensures lifetime of the locked memcg. Caller is responsible > + * for the lifetime of the page. > */ > -struct mem_cgroup *lock_page_memcg(struct page *page) > +void lock_page_memcg(struct page *page) > { > struct page *head = compound_head(page); /* rmap on tail pages */ > struct mem_cgroup *memcg; > @@ -2138,21 +2137,15 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > * The RCU lock is held throughout the transaction. The fast > * path can get away without acquiring the memcg->move_lock > * because page moving starts with an RCU grace period. > - * > - * The RCU lock also protects the memcg from being freed when > - * the page state that is going to change is the only thing > - * preventing the page itself from being freed. E.g. writeback > - * doesn't hold a page reference and relies on PG_writeback to > - * keep off truncation, migration and so forth. > */ > rcu_read_lock(); > > if (mem_cgroup_disabled()) > - return NULL; > + return; > again: > memcg = page_memcg(head); > if (unlikely(!memcg)) > - return NULL; > + return; > > #ifdef CONFIG_PROVE_LOCKING > local_irq_save(flags); > @@ -2161,7 +2154,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > #endif > > if (atomic_read(&memcg->moving_account) <= 0) > - return memcg; > + return; > > spin_lock_irqsave(&memcg->move_lock, flags); > if (memcg != page_memcg(head)) { > @@ -2170,24 +2163,17 @@ struct mem_cgroup *lock_page_memcg(struct page *page) > } > > /* > - * When charge migration first begins, we can have locked and > - * unlocked page stat updates happening concurrently. Track > - * the task who has the lock for unlock_page_memcg(). > + * When charge migration first begins, we can have multiple > + * critical sections holding the fast-path RCU lock and one > + * holding the slowpath move_lock. Track the task who has the > + * move_lock for unlock_page_memcg(). > */ > memcg->move_lock_task = current; > memcg->move_lock_flags = flags; > - > - return memcg; > } > EXPORT_SYMBOL(lock_page_memcg); > > -/** > - * __unlock_page_memcg - unlock and unpin a memcg > - * @memcg: the memcg > - * > - * Unlock and unpin a memcg returned by lock_page_memcg(). > - */ > -void __unlock_page_memcg(struct mem_cgroup *memcg) > +static void __unlock_page_memcg(struct mem_cgroup *memcg) > { > if (memcg && memcg->move_lock_task == current) { > unsigned long flags = memcg->move_lock_flags; > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index eb34d204d4ee..f6c2c3165d4d 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -2722,12 +2722,9 @@ EXPORT_SYMBOL(clear_page_dirty_for_io); > int test_clear_page_writeback(struct page *page) > { > struct address_space *mapping = page_mapping(page); > - struct mem_cgroup *memcg; > - struct lruvec *lruvec; > int ret; > > - memcg = lock_page_memcg(page); > - lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page)); > + lock_page_memcg(page); > if (mapping && mapping_use_writeback_tags(mapping)) { > struct inode *inode = mapping->host; > struct backing_dev_info *bdi = inode_to_bdi(inode); > @@ -2755,11 +2752,11 @@ int test_clear_page_writeback(struct page *page) > ret = TestClearPageWriteback(page); > } > if (ret) { > - dec_lruvec_state(lruvec, NR_WRITEBACK); > + dec_lruvec_page_state(page, NR_WRITEBACK); > dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); > inc_node_page_state(page, NR_WRITTEN); > } > - __unlock_page_memcg(memcg); > + unlock_page_memcg(page); > return ret; > } > > -- > 2.30.0 > >