linux-kernel - Re: [PATCH 02/13] mm: use page_off

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Message-ID: <20200918112421.GL28827@dhcp22.suse.cz>
Date:   Fri, 18 Sep 2020 13:24:21 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Chris Down <chris@...isdown.name>,
        Yafang Shao <laoar.shao@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Huang Ying <ying.huang@...el.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Jaewon Kim <jaewon31.kim@...sung.com>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] mm: use page_off_lru()

On Fri 18-09-20 04:27:13, Yu Zhao wrote:
> On Fri, Sep 18, 2020 at 09:37:00AM +0200, Michal Hocko wrote:
[...]
> 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?

Forgot to answer this part. The compound page concern is a misreading of
the patch on my end. I have missed you are using page_off_lru in this
(move_pages_to_lru) path and that you rely on release_pages to do the
clean up on you. I still find it rather awkward that page_off_lru has
such side effects but I am not deeply familiar with the reasoning
behind so I will rather shut up now.

[...]
> > > @@ -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

-- 
Michal Hocko
SUSE Labs