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>
return (lru == LRU_ACTIVE_ANON || lru == LRU_ACTIVE_FILE);
}
-struct zone_reclaim_stat {
- /*
- * The pageout code in vmscan.c keeps track of how many of the
- * mem/swap backed and file backed pages are referenced.
- * The higher the rotated/scanned ratio, the more valuable
- * that cache is.
- *
- * The anon LRU stats live in [0], file LRU stats in [1]
- */
- unsigned long recent_rotated[2];
- unsigned long recent_scanned[2];
-};
-
enum lruvec_flags {
LRUVEC_CONGESTED, /* lruvec has many dirty pages
* backed by a congested BDI
struct lruvec {
struct list_head lists[NR_LRU_LISTS];
- struct zone_reclaim_stat reclaim_stat;
+ /*
+ * These track the cost of reclaiming one LRU - file or anon -
+ * over the other. As the observed cost of reclaiming one LRU
+ * increases, the reclaim scan balance tips toward the other.
+ */
+ unsigned long anon_cost;
+ unsigned long file_cost;
/* Evictions & activations on the inactive file list */
atomic_long_t inactive_age;
/* Refaults at the time of last reclaim cycle */
/* linux/mm/swap.c */
+extern void lru_note_cost(struct lruvec *lruvec, bool file,
+ unsigned int nr_pages);
extern void lru_cache_add(struct page *);
extern void lru_add_page_tail(struct page *page, struct page *page_tail,
struct lruvec *lruvec, struct list_head *head);
{
pg_data_t *pgdat;
struct mem_cgroup_per_node *mz;
- struct zone_reclaim_stat *rstat;
- unsigned long recent_rotated[2] = {0, 0};
- unsigned long recent_scanned[2] = {0, 0};
+ unsigned long anon_cost = 0;
+ unsigned long file_cost = 0;
for_each_online_pgdat(pgdat) {
mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
- rstat = &mz->lruvec.reclaim_stat;
- recent_rotated[0] += rstat->recent_rotated[0];
- recent_rotated[1] += rstat->recent_rotated[1];
- recent_scanned[0] += rstat->recent_scanned[0];
- recent_scanned[1] += rstat->recent_scanned[1];
+ anon_cost += mz->lruvec.anon_cost;
+ file_cost += mz->lruvec.file_cost;
}
- seq_printf(m, "recent_rotated_anon %lu\n", recent_rotated[0]);
- seq_printf(m, "recent_rotated_file %lu\n", recent_rotated[1]);
- seq_printf(m, "recent_scanned_anon %lu\n", recent_scanned[0]);
- seq_printf(m, "recent_scanned_file %lu\n", recent_scanned[1]);
+ seq_printf(m, "anon_cost %lu\n", anon_cost);
+ seq_printf(m, "file_cost %lu\n", file_cost);
}
#endif
}
}
-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,
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,
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));
}
}
__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));
}
}
bool file = is_file_lru(lru);
enum vm_event_item item;
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
- struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
bool stalled = false;
while (unlikely(too_many_isolated(pgdat, file, sc))) {
&nr_scanned, sc, lru);
__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
- reclaim_stat->recent_scanned[file] += nr_taken;
item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
if (!cgroup_reclaim(sc))
__count_vm_events(item, nr_scanned);
move_pages_to_lru(lruvec, &page_list);
__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
- reclaim_stat->recent_rotated[0] += stat.nr_activate[0];
- reclaim_stat->recent_rotated[1] += stat.nr_activate[1];
+ /*
+ * Rotating pages costs CPU without actually
+ * progressing toward the reclaim goal.
+ */
+ lru_note_cost(lruvec, 0, stat.nr_activate[0]);
+ lru_note_cost(lruvec, 1, stat.nr_activate[1]);
item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
if (!cgroup_reclaim(sc))
__count_vm_events(item, nr_reclaimed);
LIST_HEAD(l_active);
LIST_HEAD(l_inactive);
struct page *page;
- struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
unsigned nr_deactivate, nr_activate;
unsigned nr_rotated = 0;
int file = is_file_lru(lru);
&nr_scanned, sc, lru);
__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
- reclaim_stat->recent_scanned[file] += nr_taken;
__count_vm_events(PGREFILL, nr_scanned);
__count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
* helps balance scan pressure between file and anonymous pages in
* get_scan_count.
*/
- reclaim_stat->recent_rotated[file] += nr_rotated;
+ lru_note_cost(lruvec, file, nr_rotated);
nr_activate = move_pages_to_lru(lruvec, &l_active);
nr_deactivate = move_pages_to_lru(lruvec, &l_inactive);
{
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
int swappiness = mem_cgroup_swappiness(memcg);
- struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
u64 fraction[2];
u64 denominator = 0; /* gcc */
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
unsigned long anon_prio, file_prio;
enum scan_balance scan_balance;
unsigned long anon, file;
+ unsigned long totalcost;
unsigned long ap, fp;
enum lru_list lru;
lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES);
spin_lock_irq(&pgdat->lru_lock);
- if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
- reclaim_stat->recent_scanned[0] /= 2;
- reclaim_stat->recent_rotated[0] /= 2;
- }
-
- if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
- reclaim_stat->recent_scanned[1] /= 2;
- reclaim_stat->recent_rotated[1] /= 2;
+ totalcost = lruvec->anon_cost + lruvec->file_cost;
+ if (unlikely(totalcost > (anon + file) / 4)) {
+ lruvec->anon_cost /= 2;
+ lruvec->file_cost /= 2;
+ totalcost /= 2;
}
/*
* The amount of pressure on anon vs file pages is inversely
- * proportional to the fraction of recently scanned pages on
- * each list that were recently referenced and in active use.
+ * proportional to the assumed cost of reclaiming each list,
+ * as determined by the share of pages that are likely going
+ * to refault or rotate on each list (recently referenced),
+ * times the relative IO cost of bringing back a swapped out
+ * anonymous page vs reloading a filesystem page (swappiness).
*/
- ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
- ap /= reclaim_stat->recent_rotated[0] + 1;
+ ap = anon_prio * (totalcost + 1);
+ ap /= lruvec->anon_cost + 1;
- fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
- fp /= reclaim_stat->recent_rotated[1] + 1;
+ fp = file_prio * (totalcost + 1);
+ fp /= lruvec->file_cost + 1;
spin_unlock_irq(&pgdat->lru_lock);
fraction[0] = ap;
git.samba.org / sfrench / cifs-2.6.git / commitdiff