mm: thrash detection-based file cache sizing

The VM maintains cached filesystem pages on two types of lists.  One
list holds the pages recently faulted into the cache, the other list
holds pages that have been referenced repeatedly on that first list.
The idea is to prefer reclaiming young pages over those that have shown
to benefit from caching in the past.  We call the recently usedbut
ultimately was not significantly better than a FIFO policy and still
thrashed cache based on eviction speed, rather than actual demand for
cache.

This patch solves one half of the problem by decoupling the ability to
detect working set changes from the inactive list size.  By maintaining
a history of recently evicted file pages it can detect frequently used
pages with an arbitrarily small inactive list size, and subsequently
apply pressure on the active list based on actual demand for cache, not
just overall eviction speed.

Every zone maintains a counter that tracks inactive list aging speed.
When a page is evicted, a snapshot of this counter is stored in the
now-empty page cache radix tree slot.  On refault, the minimum access
distance of the page can be assessed, to evaluate whether the page
should be part of the active list or not.

This fixes the VM's blindness towards working set changes in excess of
the inactive list.  And it's the foundation to further improve the
protection ability and reduce the minimum inactive list size of 50%.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Metin Doslu <metin@citusdata.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ozgun Erdogan <ozgun@citusdata.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin <klamm@yandex-team.ru>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 5 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2a0bb8f..1f56a80 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -523,7 +523,8 @@ static pageout_t pageout(struct page *page, struct address_space *mapping,
  * Same as remove_mapping, but if the page is removed from the mapping, it
  * gets returned with a refcount of 0.
  */
-static int __remove_mapping(struct address_space *mapping, struct page *page)
+static int __remove_mapping(struct address_space *mapping, struct page *page,
+			    bool reclaimed)
 {
 	BUG_ON(!PageLocked(page));
 	BUG_ON(mapping != page_mapping(page));
@@ -569,10 +570,23 @@ static int __remove_mapping(struct address_space *mapping, struct page *page)
 		swapcache_free(swap, page);
 	} else {
 		void (*freepage)(struct page *);
+		void *shadow = NULL;
 
 		freepage = mapping->a_ops->freepage;
-
-		__delete_from_page_cache(page, NULL);
+		/*
+		 * Remember a shadow entry for reclaimed file cache in
+		 * order to detect refaults, thus thrashing, later on.
+		 *
+		 * But don't store shadows in an address space that is
+		 * already exiting.  This is not just an optizimation,
+		 * inode reclaim needs to empty out the radix tree or
+		 * the nodes are lost.  Don't plant shadows behind its
+		 * back.
+		 */
+		if (reclaimed && page_is_file_cache(page) &&
+		    !mapping_exiting(mapping))
+			shadow = workingset_eviction(mapping, page);
+		__delete_from_page_cache(page, shadow);
 		spin_unlock_irq(&mapping->tree_lock);
 		mem_cgroup_uncharge_cache_page(page);
 
@@ -595,7 +609,7 @@ cannot_free:
  */
 int remove_mapping(struct address_space *mapping, struct page *page)
 {
-	if (__remove_mapping(mapping, page)) {
+	if (__remove_mapping(mapping, page, false)) {
 		/*
 		 * Unfreezing the refcount with 1 rather than 2 effectively
 		 * drops the pagecache ref for us without requiring another
@@ -1065,7 +1079,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			}
 		}
 
-		if (!mapping || !__remove_mapping(mapping, page))
+		if (!mapping || !__remove_mapping(mapping, page, true))
 			goto keep_locked;
 
 		/*