Re: [PATCH] mm/memcontrol: update lruvec counters in mem_cgroup_move_account

[Konstantin Khlebnikov]

On 15/10/2019 13.36, Michal Hocko wrote:
> On Tue 15-10-19 11:44:22, Konstantin Khlebnikov wrote:
> > On 15/10/2019 11.20, Michal Hocko wrote:
> > > On Tue 15-10-19 11:09:59, Konstantin Khlebnikov wrote:
> > > > Mapped, dirty and writeback pages are also counted in per-lruvec stats.
> > > > These counters needs update when page is moved between cgroups.
> > >
> > > Please describe the user visible effect.
> >
> > Surprisingly I don't see any users at this moment.
> > So, there is no effect in mainline kernel.
>
> Those counters are exported right? Or do we exclude them for v1?

It seems per-lruvec statistics is not exposed anywhere.
And per-lruvec NR_FILE_MAPPED, NR_FILE_DIRTY, NR_WRITEBACK never had users.

I've found this because I'm using mem_cgroup_move_account for recharging
pages at mlock and playing right now with debug for memory cgroup which
validates statistics and counters when cgroup dies.

> > > > Fixes: 00f3ca2c2d66 ("mm: memcontrol: per-lruvec stats infrastructure")
> > > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> > >
> > > We want Cc: stable I suspect because broken stats might be really
> > > misleading.
> > >
> > > The patch looks ok to me otherwise
> > > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > >
> > > > ---
> > > >    mm/memcontrol.c |   18 ++++++++++++------
> > > >    1 file changed, 12 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > > index bdac56009a38..363106578876 100644
> > > > --- a/mm/memcontrol.c
> > > > +++ b/mm/memcontrol.c
> > > > @@ -5420,6 +5420,8 @@ static int mem_cgroup_move_account(struct page *page,
> > > >    				   struct mem_cgroup *from,
> > > >    				   struct mem_cgroup *to)
> > > >    {
> > > > +	struct lruvec *from_vec, *to_vec;
> > > > +	struct pglist_data *pgdat;
> > > >    	unsigned long flags;
> > > >    	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
> > > >    	int ret;
> > > > @@ -5443,11 +5445,15 @@ static int mem_cgroup_move_account(struct page *page,
> > > >    	anon = PageAnon(page);
> > > > +	pgdat = page_pgdat(page);
> > > > +	from_vec = mem_cgroup_lruvec(pgdat, from);
> > > > +	to_vec = mem_cgroup_lruvec(pgdat, to);
> > > > +
> > > >    	spin_lock_irqsave(&from->move_lock, flags);
> > > >    	if (!anon && page_mapped(page)) {
> > > > -		__mod_memcg_state(from, NR_FILE_MAPPED, -nr_pages);
> > > > -		__mod_memcg_state(to, NR_FILE_MAPPED, nr_pages);
> > > > +		__mod_lruvec_state(from_vec, NR_FILE_MAPPED, -nr_pages);
> > > > +		__mod_lruvec_state(to_vec, NR_FILE_MAPPED, nr_pages);
> > > >    	}
> > > >    	/*
> > > > @@ -5459,14 +5465,14 @@ static int mem_cgroup_move_account(struct page *page,
> > > >    		struct address_space *mapping = page_mapping(page);
> > > >    		if (mapping_cap_account_dirty(mapping)) {
> > > > -			__mod_memcg_state(from, NR_FILE_DIRTY, -nr_pages);
> > > > -			__mod_memcg_state(to, NR_FILE_DIRTY, nr_pages);
> > > > +			__mod_lruvec_state(from_vec, NR_FILE_DIRTY, -nr_pages);
> > > > +			__mod_lruvec_state(to_vec, NR_FILE_DIRTY, nr_pages);
> > > >    		}
> > > >    	}
> > > >    	if (PageWriteback(page)) {
> > > > -		__mod_memcg_state(from, NR_WRITEBACK, -nr_pages);
> > > > -		__mod_memcg_state(to, NR_WRITEBACK, nr_pages);
> > > > +		__mod_lruvec_state(from_vec, NR_WRITEBACK, -nr_pages);
> > > > +		__mod_lruvec_state(to_vec, NR_WRITEBACK, nr_pages);
> > > >    	}
> > > >    #ifdef CONFIG_TRANSPARENT_HUGEPAGE