Re: [PATCH v2] mm: exclude isolated non-lru pages from NR_ISOLATED_ANON or NR_ISOLATED_FILE.

[Michal Hocko <mhocko@kernel.org>]

On Mon 17-10-16 08:06:18, Minchan Kim wrote:
> Hi Michal,
> 
> On Sat, Oct 15, 2016 at 09:10:45AM +0200, Michal Hocko wrote:
> > On Sat 15-10-16 00:26:33, Minchan Kim wrote:
> > > On Fri, Oct 14, 2016 at 05:03:55PM +0200, Michal Hocko wrote:
> > [...]
> > > > diff --git a/mm/compaction.c b/mm/compaction.c
> > > > index 0409a4ad6ea1..6584705a46f6 100644
> > > > --- a/mm/compaction.c
> > > > +++ b/mm/compaction.c
> > > > @@ -685,7 +685,8 @@ static bool too_many_isolated(struct zone *zone)
> > > >   */
> > > >  static unsigned long
> > > >  isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> > > > -			unsigned long end_pfn, isolate_mode_t isolate_mode)
> > > > +			unsigned long end_pfn, isolate_mode_t isolate_mode,
> > > > +			unsigned long *isolated_file, unsigned long *isolated_anon)
> > > >  {
> > > >  	struct zone *zone = cc->zone;
> > > >  	unsigned long nr_scanned = 0, nr_isolated = 0;
> > > > @@ -866,6 +867,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> > > >  
> > > >  		/* Successfully isolated */
> > > >  		del_page_from_lru_list(page, lruvec, page_lru(page));
> > > > +		if (page_is_file_cache(page))
> > > > +			(*isolated_file)++;
> > > > +		else
> > > > +			(*isolated_anon)++;
> > > >  
> > > >  isolate_success:
> > > >  		list_add(&page->lru, &cc->migratepages);
> > > > 
> > > > Makes more sense?
> > > 
> > > It is doable for isolation part. IOW, maybe we can make acct_isolated
> > > simple with those counters but we need to handle migrate, putback part.
> > > If you want to remove the check of __PageMoable with those counter, it
> > > means we should pass the counter on every functions related migration
> > > where isolate, migrate, putback parts.
> > 
> > OK, I see. Can we just get rid of acct_isolated altogether? Why cannot
> > we simply update NR_ISOLATED_* while isolating pages? Just looking at
> > isolate_migratepages_block:
> > 			acct_isolated(zone, cc);
> > 			putback_movable_pages(&cc->migratepages);
> > 
> > suggests we are doing something suboptimal. I guess we cannot get rid of
> > __PageMoveble checks which is sad because that just adds a lot of
> > confusion because checking for !__PageMovable(page) for LRU pages is
> > just a head scratcher (LRU pages are movable arent' they?). Maybe it
> > would be even good to get rid of this misnomer. PageNonLRUMovable?
> 
> Yeah, I hated the naming but didn't have a good idea.
> PageNonLRUMovable, definitely, one I thought as candidate but dropped
> by lenghthy naming. If others don't object, I am happy to change it.

Yes it is long but it is less confusing because it is just utterly
confusing to test for LRU pages with !__PageMovable when in fact they
are movable. Heck even unreclaimable pages are movable unless explicitly
configured to not be.
 
> > Anyway, I would suggest to do something like this. Batching NR_ISOLATED*
> > just doesn't make all that much sense as these are per-cpu and the
> > resulting code seems to be easier without it.
> 
> Agree. Could you resend it as formal patch?

Sure, what do you think about the following? I haven't marked it for
stable because there was no bug report for it AFAIU.
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