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mm/vmscan.c: refactor shrink_node()
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This patch refactors shrink_node() to improve readability for the
upcoming changes to mm/vmscan.c.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
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@yuzhaogoogle @xanmod
yuzhaogoogle authored and xanmod committed Jan 12, 2022
1 parent 1d3d377 commit 22380a1
Showing 1 changed file with 104 additions and 94 deletions.
198 changes: 104 additions & 94 deletions mm/vmscan.c
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Expand Up @@ -2716,6 +2716,109 @@ enum scan_balance {
SCAN_FILE,
};

static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
{
unsigned long file;
struct lruvec *target_lruvec;

target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);

/*
* Flush the memory cgroup stats, so that we read accurate per-memcg
* lruvec stats for heuristics.
*/
mem_cgroup_flush_stats();

/*
* Determine the scan balance between anon and file LRUs.
*/
spin_lock_irq(&target_lruvec->lru_lock);
sc->anon_cost = target_lruvec->anon_cost;
sc->file_cost = target_lruvec->file_cost;
spin_unlock_irq(&target_lruvec->lru_lock);

/*
* Target desirable inactive:active list ratios for the anon
* and file LRU lists.
*/
if (!sc->force_deactivate) {
unsigned long refaults;

refaults = lruvec_page_state(target_lruvec,
WORKINGSET_ACTIVATE_ANON);
if (refaults != target_lruvec->refaults[0] ||
inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
sc->may_deactivate |= DEACTIVATE_ANON;
else
sc->may_deactivate &= ~DEACTIVATE_ANON;

/*
* When refaults are being observed, it means a new
* workingset is being established. Deactivate to get
* rid of any stale active pages quickly.
*/
refaults = lruvec_page_state(target_lruvec,
WORKINGSET_ACTIVATE_FILE);
if (refaults != target_lruvec->refaults[1] ||
inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
sc->may_deactivate |= DEACTIVATE_FILE;
else
sc->may_deactivate &= ~DEACTIVATE_FILE;
} else
sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;

/*
* If we have plenty of inactive file pages that aren't
* thrashing, try to reclaim those first before touching
* anonymous pages.
*/
file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
sc->cache_trim_mode = 1;
else
sc->cache_trim_mode = 0;

/*
* Prevent the reclaimer from falling into the cache trap: as
* cache pages start out inactive, every cache fault will tip
* the scan balance towards the file LRU. And as the file LRU
* shrinks, so does the window for rotation from references.
* This means we have a runaway feedback loop where a tiny
* thrashing file LRU becomes infinitely more attractive than
* anon pages. Try to detect this based on file LRU size.
*/
if (!cgroup_reclaim(sc)) {
unsigned long total_high_wmark = 0;
unsigned long free, anon;
int z;

free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
file = node_page_state(pgdat, NR_ACTIVE_FILE) +
node_page_state(pgdat, NR_INACTIVE_FILE);

for (z = 0; z < MAX_NR_ZONES; z++) {
struct zone *zone = &pgdat->node_zones[z];

if (!managed_zone(zone))
continue;

total_high_wmark += high_wmark_pages(zone);
}

/*
* Consider anon: if that's low too, this isn't a
* runaway file reclaim problem, but rather just
* extreme pressure. Reclaim as per usual then.
*/
anon = node_page_state(pgdat, NR_INACTIVE_ANON);

sc->file_is_tiny =
file + free <= total_high_wmark &&
!(sc->may_deactivate & DEACTIVATE_ANON) &&
anon >> sc->priority;
}
}

/*
* Determine how aggressively the anon and file LRU lists should be
* scanned. The relative value of each set of LRU lists is determined
Expand Down Expand Up @@ -3186,109 +3289,16 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
unsigned long nr_reclaimed, nr_scanned;
struct lruvec *target_lruvec;
bool reclaimable = false;
unsigned long file;

target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);

again:
/*
* Flush the memory cgroup stats, so that we read accurate per-memcg
* lruvec stats for heuristics.
*/
mem_cgroup_flush_stats();

memset(&sc->nr, 0, sizeof(sc->nr));

nr_reclaimed = sc->nr_reclaimed;
nr_scanned = sc->nr_scanned;

/*
* Determine the scan balance between anon and file LRUs.
*/
spin_lock_irq(&target_lruvec->lru_lock);
sc->anon_cost = target_lruvec->anon_cost;
sc->file_cost = target_lruvec->file_cost;
spin_unlock_irq(&target_lruvec->lru_lock);

/*
* Target desirable inactive:active list ratios for the anon
* and file LRU lists.
*/
if (!sc->force_deactivate) {
unsigned long refaults;

refaults = lruvec_page_state(target_lruvec,
WORKINGSET_ACTIVATE_ANON);
if (refaults != target_lruvec->refaults[0] ||
inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
sc->may_deactivate |= DEACTIVATE_ANON;
else
sc->may_deactivate &= ~DEACTIVATE_ANON;

/*
* When refaults are being observed, it means a new
* workingset is being established. Deactivate to get
* rid of any stale active pages quickly.
*/
refaults = lruvec_page_state(target_lruvec,
WORKINGSET_ACTIVATE_FILE);
if (refaults != target_lruvec->refaults[1] ||
inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
sc->may_deactivate |= DEACTIVATE_FILE;
else
sc->may_deactivate &= ~DEACTIVATE_FILE;
} else
sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;

/*
* If we have plenty of inactive file pages that aren't
* thrashing, try to reclaim those first before touching
* anonymous pages.
*/
file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
sc->cache_trim_mode = 1;
else
sc->cache_trim_mode = 0;

/*
* Prevent the reclaimer from falling into the cache trap: as
* cache pages start out inactive, every cache fault will tip
* the scan balance towards the file LRU. And as the file LRU
* shrinks, so does the window for rotation from references.
* This means we have a runaway feedback loop where a tiny
* thrashing file LRU becomes infinitely more attractive than
* anon pages. Try to detect this based on file LRU size.
*/
if (!cgroup_reclaim(sc)) {
unsigned long total_high_wmark = 0;
unsigned long free, anon;
int z;

free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
file = node_page_state(pgdat, NR_ACTIVE_FILE) +
node_page_state(pgdat, NR_INACTIVE_FILE);

for (z = 0; z < MAX_NR_ZONES; z++) {
struct zone *zone = &pgdat->node_zones[z];
if (!managed_zone(zone))
continue;

total_high_wmark += high_wmark_pages(zone);
}

/*
* Consider anon: if that's low too, this isn't a
* runaway file reclaim problem, but rather just
* extreme pressure. Reclaim as per usual then.
*/
anon = node_page_state(pgdat, NR_INACTIVE_ANON);

sc->file_is_tiny =
file + free <= total_high_wmark &&
!(sc->may_deactivate & DEACTIVATE_ANON) &&
anon >> sc->priority;
}
prepare_scan_count(pgdat, sc);

shrink_node_memcgs(pgdat, sc);

Expand Down

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