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Fri, 18 Sep 2020 03:27:20 -0700 (PDT) Date: Fri, 18 Sep 2020 04:27:13 -0600 From: Yu Zhao To: Michal Hocko Cc: Andrew Morton , Alex Shi , Steven Rostedt , Ingo Molnar , Johannes Weiner , Vladimir Davydov , Roman Gushchin , Shakeel Butt , Chris Down , Yafang Shao , Vlastimil Babka , Huang Ying , Pankaj Gupta , Matthew Wilcox , Konstantin Khlebnikov , Minchan Kim , Jaewon Kim , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 02/13] mm: use page_off_lru() Message-ID: <20200918102713.GB1004594@google.com> References: <20200918030051.650890-1-yuzhao@google.com> <20200918030051.650890-3-yuzhao@google.com> <20200918073700.GE28827@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200918073700.GE28827@dhcp22.suse.cz> 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 Fri, Sep 18, 2020 at 09:37:00AM +0200, Michal Hocko wrote: > On Thu 17-09-20 21:00:40, Yu Zhao wrote: > > This patch replaces the only open-coded __ClearPageActive() with > > page_off_lru(). There is no open-coded __ClearPageUnevictable()s. > > > > Before this patch, we have: > > __ClearPageActive() > > add_page_to_lru_list() > > > > After this patch, we have: > > page_off_lru() > > if PageUnevictable() > > __ClearPageUnevictable() > > else if PageActive() > > __ClearPageActive() > > add_page_to_lru_list() > > > > Checking PageUnevictable() shouldn't be a problem because these two > > flags are mutually exclusive. Leaking either will trigger bad_page(). > > I am sorry but the changelog is really hard to grasp. What are you > trying to achieve, why and why it is safe. This should be a general > outline for any patch. I have already commented on the previous patch > and asked you for the explanation why removing __ClearPageActive from > this path is desirable and safe. I have specifically asked to clarify > the compound page situation as that is using its oen destructor in the > freeing path and that might result in page_off_lru to be not called. Haven't I explained we are NOT removing __ClearPageActive()? Is my notion of the code structure above confusing you? Or 'open-coded' could mean different things? And I have asked this before: why does 'the compound page situation' even matter here? Perhaps if you could give a concrete example related to the code change and help me understand your concern? > > Signed-off-by: Yu Zhao > > --- > > mm/vmscan.c | 6 +----- > > 1 file changed, 1 insertion(+), 5 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 503fc5e1fe32..f257d2f61574 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -1845,7 +1845,6 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec, > > int nr_pages, nr_moved = 0; > > LIST_HEAD(pages_to_free); > > struct page *page; > > - enum lru_list lru; > > > > while (!list_empty(list)) { > > page = lru_to_page(list); > > @@ -1860,14 +1859,11 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec, > > lruvec = mem_cgroup_page_lruvec(page, pgdat); > > > > SetPageLRU(page); > > - lru = page_lru(page); > > - > > add_page_to_lru_list(page, lruvec, lru); > > > > if (put_page_testzero(page)) { > > __ClearPageLRU(page); > > - __ClearPageActive(page); > > - del_page_from_lru_list(page, lruvec, lru); > > + del_page_from_lru_list(page, lruvec, page_off_lru(page)); > > > > if (unlikely(PageCompound(page))) { > > spin_unlock_irq(&pgdat->lru_lock); > > -- > > 2.28.0.681.g6f77f65b4e-goog > > -- > Michal Hocko > SUSE Labs