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.
---
>From 3b2bd4486f36ada9f6dc86d3946855281455ba9f Mon Sep 17 00:00:00 2001
From: Ming Ling <ming.ling@spreadtrum.com>
Date: Mon, 17 Oct 2016 10:26:50 +0200
Subject: [PATCH] mm, compaction: fix NR_ISOLATED_* stats for pfn based
 migration

Since bda807d44454 ("mm: migrate: support non-lru movable page
migration") isolate_migratepages_block) can isolate !PageLRU pages which
would acct_isolated account as NR_ISOLATED_*. Accounting these non-lru
pages NR_ISOLATED_{ANON,FILE} doesn't make any sense and it can misguide
heuristics based on those counters such as pgdat_reclaimable_pages resp.
too_many_isolated which would lead to unexpected stalls during the
direct reclaim without any good reason. Note that
__alloc_contig_migrate_range can isolate a lot of pages at once.

On mobile devices such as 512M ram android Phone, it may use a big zram
swap. In some cases zram(zsmalloc) uses too many non-lru but migratedable
pages, such as:

      MemTotal: 468148 kB
      Normal free:5620kB
      Free swap:4736kB
      Total swap:409596kB
      ZRAM: 164616kB(zsmalloc non-lru pages)
      active_anon:60700kB
      inactive_anon:60744kB
      active_file:34420kB
      inactive_file:37532kB

Fix this by only accounting lru pages to NR_ISOLATED_* in
isolate_migratepages_block right after they were isolated and we still
know they were on LRU. Drop acct_isolated because it is called after the
fact and we've lost that information. Batching per-cpu counter doesn't
make much improvement anyway. Also make sure that we uncharge only LRU
pages when putting them back on the LRU in putback_movable_pages resp.
when unmap_and_move migrates the page.

Fixes: bda807d44454 ("mm: migrate: support non-lru movable page migration")
Signed-off-by: Ming Ling <ming.ling@spreadtrum.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/compaction.c | 25 +++----------------------
 mm/migrate.c    | 15 +++++++++++----
 2 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 0409a4ad6ea1..df1fd0c20e5c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -634,22 +634,6 @@ isolate_freepages_range(struct compact_control *cc,
 	return pfn;
 }
 
-/* Update the number of anon and file isolated pages in the zone */
-static void acct_isolated(struct zone *zone, struct compact_control *cc)
-{
-	struct page *page;
-	unsigned int count[2] = { 0, };
-
-	if (list_empty(&cc->migratepages))
-		return;
-
-	list_for_each_entry(page, &cc->migratepages, lru)
-		count[!!page_is_file_cache(page)]++;
-
-	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON, count[0]);
-	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, count[1]);
-}
-
 /* Similar to reclaim, but different enough that they don't share logic */
 static bool too_many_isolated(struct zone *zone)
 {
@@ -866,6 +850,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 		/* Successfully isolated */
 		del_page_from_lru_list(page, lruvec, page_lru(page));
+		inc_node_page_state(zone->zone_pgdat,
+				NR_ISOLATED_ANON + page_is_file_cache(page));
 
 isolate_success:
 		list_add(&page->lru, &cc->migratepages);
@@ -902,7 +888,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 				spin_unlock_irqrestore(zone_lru_lock(zone), flags);
 				locked = false;
 			}
-			acct_isolated(zone, cc);
 			putback_movable_pages(&cc->migratepages);
 			cc->nr_migratepages = 0;
 			cc->last_migrated_pfn = 0;
@@ -988,7 +973,6 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
 			break;
 	}
-	acct_isolated(cc->zone, cc);
 
 	return pfn;
 }
@@ -1258,10 +1242,8 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 		low_pfn = isolate_migratepages_block(cc, low_pfn,
 						block_end_pfn, isolate_mode);
 
-		if (!low_pfn || cc->contended) {
-			acct_isolated(zone, cc);
+		if (!low_pfn || cc->contended)
 			return ISOLATE_ABORT;
-		}
 
 		/*
 		 * Either we isolated something and proceed with migration. Or
@@ -1271,7 +1253,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 		break;
 	}
 
-	acct_isolated(zone, cc);
 	/* Record where migration scanner will be restarted. */
 	cc->migrate_pfn = low_pfn;
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 99250aee1ac1..66ce6b490b13 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -168,8 +168,6 @@ void putback_movable_pages(struct list_head *l)
 			continue;
 		}
 		list_del(&page->lru);
-		dec_node_page_state(page, NR_ISOLATED_ANON +
-				page_is_file_cache(page));
 		/*
 		 * We isolated non-lru movable page so here we can use
 		 * __PageMovable because LRU page's mapping cannot have
@@ -186,6 +184,8 @@ void putback_movable_pages(struct list_head *l)
 			put_page(page);
 		} else {
 			putback_lru_page(page);
+			dec_node_page_state(page, NR_ISOLATED_ANON +
+					page_is_file_cache(page));
 		}
 	}
 }
@@ -1121,8 +1121,15 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 		 * restored.
 		 */
 		list_del(&page->lru);
-		dec_node_page_state(page, NR_ISOLATED_ANON +
-				page_is_file_cache(page));
+
+		/*
+		 * Compaction can migrate also non-LRU pages which are
+		 * not accounted to NR_ISOLATED_*. They can be recognized
+		 * as __PageMovable
+		 */
+		if (likely(!__PageMovable(page)))
+			dec_node_page_state(page, NR_ISOLATED_ANON +
+					page_is_file_cache(page));
 	}
 
 	/*
-- 
2.9.3


-- 
Michal Hocko
SUSE Labs