From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hugh Dickins Subject: Re: [PATCH] mm: page-writeback: simplify memcg handling in test_clear_page_writeback() Date: Tue, 9 Feb 2021 21:16:37 -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=Q8+AD77bMtoNW/HBzmZ8xMNYIgN4sAwD1/ADY3ZtEEk=; b=Fdroa3m70eD8+7KTxXuHTcUNnT7RKmI2+/ujf5yGEJfyh0W9IHuWdQ5VrHoRK6KiKO orVrw72k5YjskoOG5UvgLdG/VhwDwAzL+AT5d8n9kKs8NOrUjf1eD9km4BYGH86kloyE na4Au9OoCTeFEnN4rZy0olzery/o76zJWHL/F4q0Er3uC2Wu2BN/BydsGVBJ9vFNEjv3 DGOM99xnrf4CLCxsyb52Jb4BBg+fytIkav8i4ZzrLv+joPRR4Zjr5LcjOKlhUVM9M64i yf1ht/CMGODtIeTCmM5Y/XlMCZ7q21rDcMYbIM7kF3RiQZGI0RCBgeQvIwBdMrMHhydS lARA== In-Reply-To: <20210209214543.112655-1-hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org> List-ID: Content-Type: TEXT/PLAIN; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Johannes Weiner Cc: Andrew Morton , Hugh Dickins , 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 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: 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. > > Signed-off-by: Johannes Weiner Acked-by: Hugh Dickins > --- > mm/page-writeback.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > 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