* the only thing eating into inactive list space is active pages.
*
*
- * Activating refaulting pages
+ * Refaulting inactive pages
*
* All that is known about the active list is that the pages have been
* accessed more than once in the past. This means that at any given
* used less frequently than the refaulting page - or even not used at
* all anymore.
*
+ * That means if inactive cache is refaulting with a suitable refault
+ * distance, we assume the cache workingset is transitioning and put
+ * pressure on the current active list.
+ *
* If this is wrong and demotion kicks in, the pages which are truly
* used more frequently will be reactivated while the less frequently
* used once will be evicted from memory.
* But if this is right, the stale pages will be pushed out of memory
* and the used pages get to stay in cache.
*
+ * Refaulting active pages
+ *
+ * If on the other hand the refaulting pages have recently been
+ * deactivated, it means that the active list is no longer protecting
+ * actively used cache from reclaim. The cache is NOT transitioning to
+ * a different workingset; the existing workingset is thrashing in the
+ * space allocated to the page cache.
+ *
*
* Implementation
*
*/
#define EVICTION_SHIFT (RADIX_TREE_EXCEPTIONAL_ENTRY + \
- NODES_SHIFT + \
- MEM_CGROUP_ID_SHIFT)
+ 1 + NODES_SHIFT + MEM_CGROUP_ID_SHIFT)
#define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
/*
*/
static unsigned int bucket_order __read_mostly;
-static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction)
+static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
+ bool workingset)
{
eviction >>= bucket_order;
eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
+ eviction = (eviction << 1) | workingset;
eviction = (eviction << RADIX_TREE_EXCEPTIONAL_SHIFT);
return (void *)(eviction | RADIX_TREE_EXCEPTIONAL_ENTRY);
}
static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
- unsigned long *evictionp)
+ unsigned long *evictionp, bool *workingsetp)
{
unsigned long entry = (unsigned long)shadow;
int memcgid, nid;
+ bool workingset;
entry >>= RADIX_TREE_EXCEPTIONAL_SHIFT;
+ workingset = entry & 1;
+ entry >>= 1;
nid = entry & ((1UL << NODES_SHIFT) - 1);
entry >>= NODES_SHIFT;
memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
*memcgidp = memcgid;
*pgdat = NODE_DATA(nid);
*evictionp = entry << bucket_order;
+ *workingsetp = workingset;
}
/**
*/
void *workingset_eviction(struct address_space *mapping, struct page *page)
{
- struct mem_cgroup *memcg = page_memcg(page);
struct pglist_data *pgdat = page_pgdat(page);
+ struct mem_cgroup *memcg = page_memcg(page);
int memcgid = mem_cgroup_id(memcg);
unsigned long eviction;
struct lruvec *lruvec;
lruvec = mem_cgroup_lruvec(pgdat, memcg);
eviction = atomic_long_inc_return(&lruvec->inactive_age);
- return pack_shadow(memcgid, pgdat, eviction);
+ return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page));
}
/**
* workingset_refault - evaluate the refault of a previously evicted page
+ * @page: the freshly allocated replacement page
* @shadow: shadow entry of the evicted page
*
* Calculates and evaluates the refault distance of the previously
* evicted page in the context of the node it was allocated in.
- *
- * Returns %true if the page should be activated, %false otherwise.
*/
-bool workingset_refault(void *shadow)
+void workingset_refault(struct page *page, void *shadow)
{
unsigned long refault_distance;
+ struct pglist_data *pgdat;
unsigned long active_file;
struct mem_cgroup *memcg;
unsigned long eviction;
struct lruvec *lruvec;
unsigned long refault;
- struct pglist_data *pgdat;
+ bool workingset;
int memcgid;
- unpack_shadow(shadow, &memcgid, &pgdat, &eviction);
+ unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
rcu_read_lock();
/*
* configurations instead.
*/
memcg = mem_cgroup_from_id(memcgid);
- if (!mem_cgroup_disabled() && !memcg) {
- rcu_read_unlock();
- return false;
- }
+ if (!mem_cgroup_disabled() && !memcg)
+ goto out;
lruvec = mem_cgroup_lruvec(pgdat, memcg);
refault = atomic_long_read(&lruvec->inactive_age);
active_file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES);
/*
- * The unsigned subtraction here gives an accurate distance
- * across inactive_age overflows in most cases.
+ * Calculate the refault distance
*
- * There is a special case: usually, shadow entries have a
- * short lifetime and are either refaulted or reclaimed along
- * with the inode before they get too old. But it is not
- * impossible for the inactive_age to lap a shadow entry in
- * the field, which can then can result in a false small
- * refault distance, leading to a false activation should this
- * old entry actually refault again. However, earlier kernels
- * used to deactivate unconditionally with *every* reclaim
- * invocation for the longest time, so the occasional
- * inappropriate activation leading to pressure on the active
- * list is not a problem.
+ * The unsigned subtraction here gives an accurate distance
+ * across inactive_age overflows in most cases. There is a
+ * special case: usually, shadow entries have a short lifetime
+ * and are either refaulted or reclaimed along with the inode
+ * before they get too old. But it is not impossible for the
+ * inactive_age to lap a shadow entry in the field, which can
+ * then result in a false small refault distance, leading to a
+ * false activation should this old entry actually refault
+ * again. However, earlier kernels used to deactivate
+ * unconditionally with *every* reclaim invocation for the
+ * longest time, so the occasional inappropriate activation
+ * leading to pressure on the active list is not a problem.
*/
refault_distance = (refault - eviction) & EVICTION_MASK;
inc_lruvec_state(lruvec, WORKINGSET_REFAULT);
- if (refault_distance <= active_file) {
- inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
- rcu_read_unlock();
- return true;
+ /*
+ * Compare the distance to the existing workingset size. We
+ * don't act on pages that couldn't stay resident even if all
+ * the memory was available to the page cache.
+ */
+ if (refault_distance > active_file)
+ goto out;
+
+ SetPageActive(page);
+ atomic_long_inc(&lruvec->inactive_age);
+ inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
+
+ /* Page was active prior to eviction */
+ if (workingset) {
+ SetPageWorkingset(page);
+ inc_lruvec_state(lruvec, WORKINGSET_RESTORE);
}
+out:
rcu_read_unlock();
- return false;
}
/**
projects / kernel.git / commitdiff