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: Wed, 10 Feb 2021 08:22:00 -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=wc8HtUu6YXXorPykhuoj08SCrBEaocuYohr96nbgn+w=; b=fpSdWoUW/YxqsP5HrQVPzNsTdbTt5mOIk6GqFhMMF/biAw553DP/Q7qeQJMjwPShNk 1tRCVOShdBPkTNGrIargdgle8wgQceXqCAn3IHA7g3D04Ow8R7+9FWnFmuNmYkLtRhc3 NPZRlQhxOcWweh5MO8A8cXXzWeWCBg+WAxOyFchaYUnrwwxZ4crSYQ0oL8jAS9UrwmfP CW1W7cC6X2NLISJ0M4LetFXkBGcA78Y68b1khrpiqAvP7GG9vuz60hI/o+GaUIpyObsJ SJ7LZjvLn5dEu4MAlTKTFOVnNmu8Z9Fsn7GavQTkW21qdobIJyuLdv3dBLsT3lnHDn9s ymow== 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 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. > > 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 >