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authorJohannes Weiner <hannes@cmpxchg.org>2020-06-03 16:02:53 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-03 20:09:48 -0700
commit1431d4d11abb265e79cd44bed2f5ea93f1bcc57b (patch)
treedd4a97c5d9d287ecb85ff8c73f7c3cdad1be1392 /mm/swap.c
parenta4fe1631f313f75c7dced10d9e7eda816bf0937f (diff)
mm: base LRU balancing on an explicit cost model
Currently, scan pressure between the anon and file LRU lists is balanced based on a mixture of reclaim efficiency and a somewhat vague notion of "value" of having certain pages in memory over others. That concept of value is problematic, because it has caused us to count any event that remotely makes one LRU list more or less preferrable for reclaim, even when these events are not directly comparable and impose very different costs on the system. One example is referenced file pages that we still deactivate and referenced anonymous pages that we actually rotate back to the head of the list. There is also conceptual overlap with the LRU algorithm itself. By rotating recently used pages instead of reclaiming them, the algorithm already biases the applied scan pressure based on page value. Thus, when rebalancing scan pressure due to rotations, we should think of reclaim cost, and leave assessing the page value to the LRU algorithm. Lastly, considering both value-increasing as well as value-decreasing events can sometimes cause the same type of event to be counted twice, i.e. how rotating a page increases the LRU value, while reclaiming it succesfully decreases the value. In itself this will balance out fine, but it quietly skews the impact of events that are only recorded once. The abstract metric of "value", the murky relationship with the LRU algorithm, and accounting both negative and positive events make the current pressure balancing model hard to reason about and modify. This patch switches to a balancing model of accounting the concrete, actually observed cost of reclaiming one LRU over another. For now, that cost includes pages that are scanned but rotated back to the list head. Subsequent patches will add consideration for IO caused by refaulting of recently evicted pages. Replace struct zone_reclaim_stat with two cost counters in the lruvec, and make everything that affects cost go through a new lru_note_cost() function. Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Rik van Riel <riel@surriel.com> Link: http://lkml.kernel.org/r/20200520232525.798933-9-hannes@cmpxchg.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap.c')
-rw-r--r--mm/swap.c19
1 files changed, 8 insertions, 11 deletions
diff --git a/mm/swap.c b/mm/swap.c
index 116b609c25c1..fedeb925dbfe 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -278,15 +278,12 @@ void rotate_reclaimable_page(struct page *page)
}
}
-static void update_page_reclaim_stat(struct lruvec *lruvec,
- int file, int rotated,
- unsigned int nr_pages)
+void lru_note_cost(struct lruvec *lruvec, bool file, unsigned int nr_pages)
{
- struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
-
- reclaim_stat->recent_scanned[file] += nr_pages;
- if (rotated)
- reclaim_stat->recent_rotated[file] += nr_pages;
+ if (file)
+ lruvec->file_cost += nr_pages;
+ else
+ lruvec->anon_cost += nr_pages;
}
static void __activate_page(struct page *page, struct lruvec *lruvec,
@@ -541,7 +538,7 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
if (active)
__count_vm_event(PGDEACTIVATE);
- update_page_reclaim_stat(lruvec, file, 0, hpage_nr_pages(page));
+ lru_note_cost(lruvec, !file, hpage_nr_pages(page));
}
static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
@@ -557,7 +554,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
add_page_to_lru_list(page, lruvec, lru);
__count_vm_events(PGDEACTIVATE, hpage_nr_pages(page));
- update_page_reclaim_stat(lruvec, file, 0, hpage_nr_pages(page));
+ lru_note_cost(lruvec, !file, hpage_nr_pages(page));
}
}
@@ -582,7 +579,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
__count_vm_events(PGLAZYFREE, hpage_nr_pages(page));
count_memcg_page_event(page, PGLAZYFREE);
- update_page_reclaim_stat(lruvec, 1, 0, hpage_nr_pages(page));
+ lru_note_cost(lruvec, 0, hpage_nr_pages(page));
}
}