This patch implements compaction worker thread for z3fold. This
worker does not free up any pages directly but it allows for a
denser placement of compressed objects which results in less
actual pages consumed and higher compression ratio therefore.
This patch has been checked with the latest Linus's tree.
Signed-off-by: Vitaly Wool <vitalyw...@gmail.com>
---
mm/z3fold.c | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 140 insertions(+), 26 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 014d84f..cc26ff5 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -27,6 +27,7 @@
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/preempt.h>
+#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/zpool.h>
@@ -59,6 +60,7 @@ struct z3fold_ops {
/**
* struct z3fold_pool - stores metadata for each z3fold pool
+ * @name: pool name
* @lock: protects all pool fields and first|last_chunk fields of any
* z3fold page in the pool
* @unbuddied: array of lists tracking z3fold pages that contain 2- buddies;
@@ -72,11 +74,14 @@ struct z3fold_ops {
* @unbuddied_nr: number of unbuddied z3fold pages in the pool.
* @ops: pointer to a structure of user defined operations specified at
* pool creation time.
+ * @compact_wq: workqueue for page layout background optimization
+ * @work: compaction work item
*
* This structure is allocated at pool creation time and maintains metadata
* pertaining to a particular z3fold pool.
*/
struct z3fold_pool {
+ const char *name;
rwlock_t lock;
struct list_head unbuddied[NCHUNKS];
struct list_head buddied;
@@ -86,6 +91,8 @@ struct z3fold_pool {
const struct z3fold_ops *ops;
struct zpool *zpool;
const struct zpool_ops *zpool_ops;
+ struct workqueue_struct *compact_wq;
+ struct delayed_work work;
};
enum buddy {
@@ -121,6 +128,7 @@ enum z3fold_page_flags {
UNDER_RECLAIM = 0,
PAGE_HEADLESS,
MIDDLE_CHUNK_MAPPED,
+ COMPACTION_DEFERRED,
};
/*****************
@@ -136,6 +144,9 @@ static int size_to_chunks(size_t size)
#define for_each_unbuddied_list(_iter, _begin) \
for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
+#define for_each_unbuddied_list_reverse(_iter, _end) \
+ for ((_iter) = (_end); (_iter) > 0; (_iter)--)
+
/* Initializes the z3fold header of a newly allocated z3fold page */
static struct z3fold_header *init_z3fold_page(struct page *page)
{
@@ -145,6 +156,7 @@ static struct z3fold_header *init_z3fold_page(struct page
*page)
clear_bit(UNDER_RECLAIM, &page->private);
clear_bit(PAGE_HEADLESS, &page->private);
clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
+ clear_bit(COMPACTION_DEFERRED, &page->private);
zhdr->first_chunks = 0;
zhdr->middle_chunks = 0;
@@ -211,6 +223,116 @@ static int num_free_chunks(struct z3fold_header *zhdr)
return nfree;
}
+static inline void *mchunk_memmove(struct z3fold_header *zhdr,
+ unsigned short dst_chunk)
+{
+ void *beg = zhdr;
+ return memmove(beg + (dst_chunk << CHUNK_SHIFT),
+ beg + (zhdr->start_middle << CHUNK_SHIFT),
+ zhdr->middle_chunks << CHUNK_SHIFT);
+}
+
+static int z3fold_compact_page(struct z3fold_header *zhdr, bool sync)
+{
+ struct page *page = virt_to_page(zhdr);
+ int ret = 0;
+
+ if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private)) {
+ set_bit(COMPACTION_DEFERRED, &page->private);
+ ret = -1;
+ goto out;
+ }
+
+ clear_bit(COMPACTION_DEFERRED, &page->private);
+ if (zhdr->middle_chunks != 0) {
+ if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
+ /*
+ * If we are here, no one can access this page
+ * except for z3fold_map or z3fold_free. Both
+ * will wait for page_lock to become free.
+ */
+ mchunk_memmove(zhdr, 1); /* move to the beginning */
+ zhdr->first_chunks = zhdr->middle_chunks;
+ zhdr->middle_chunks = 0;
+ zhdr->start_middle = 0;
+ zhdr->first_num++;
+ ret = 1;
+ goto out;
+ }
+ if (sync)
+ goto out;
+
+ /*
+ * These are more complicated cases: first or last object
+ * may be mapped. Luckily we don't touch these anyway.
+ *
+ * NB: moving data is expensive, so let's only do that if
+ * there's substantial gain (2+ chunks)
+ */
+ if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
+ zhdr->start_middle > zhdr->first_chunks + 2) {
+ mchunk_memmove(zhdr, zhdr->first_chunks + 1);
+ zhdr->start_middle = zhdr->first_chunks + 1;
+ ret = 1;
+ goto out;
+ }
+ if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
+ zhdr->middle_chunks + zhdr->last_chunks <=
+ NCHUNKS - zhdr->start_middle - 2) {
+ unsigned short new_start = NCHUNKS - zhdr->last_chunks -
+ zhdr->middle_chunks;
+ mchunk_memmove(zhdr, new_start);
+ zhdr->start_middle = new_start;
+ ret = 1;
+ goto out;
+ }
+ }
+out:
+ return ret;
+}
+
+#define COMPACTION_BATCH (NCHUNKS/2)
+static void z3fold_compact_work(struct work_struct *w)
+{
+ struct z3fold_pool *pool = container_of(to_delayed_work(w),
+ struct z3fold_pool, work);
+ struct z3fold_header *zhdr;
+ struct page *page;
+ int i, ret, compacted = 0;
+ bool requeue = false;
+
+ write_lock(&pool->lock);
+ for_each_unbuddied_list_reverse(i, NCHUNKS - 3) {
+ zhdr = list_empty(&pool->unbuddied[i]) ?
+ NULL : list_last_entry(&pool->unbuddied[i],
+ struct z3fold_header, buddy);
+ if (!zhdr)
+ continue;
+ page = virt_to_page(zhdr);
+ if (likely(!test_bit(COMPACTION_DEFERRED, &page->private)))
+ continue;
+ list_del(&zhdr->buddy);
+ ret = z3fold_compact_page(zhdr, false);
+ if (ret < 0)
+ requeue = true;
+ else
+ compacted += ret;
+ write_unlock(&pool->lock);
+ cond_resched();
+ write_lock(&pool->lock);
+ list_add(&zhdr->buddy,
+ &pool->unbuddied[num_free_chunks(zhdr)]);
+ if (compacted >= COMPACTION_BATCH) {
+ requeue = true;
+ break;
+ }
+ }
+ write_unlock(&pool->lock);
+ if (requeue && !delayed_work_pending(&pool->work))
+ queue_delayed_work(pool->compact_wq, &pool->work, HZ);
+}
+
+
/*****************
* API Functions
*****************/
@@ -230,7 +352,7 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp,
pool = kzalloc(sizeof(struct z3fold_pool), gfp);
if (!pool)
- return NULL;
+ goto out;
rwlock_init(&pool->lock);
for_each_unbuddied_list(i, 0)
INIT_LIST_HEAD(&pool->unbuddied[i]);
@@ -238,8 +360,17 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp,
INIT_LIST_HEAD(&pool->lru);
atomic64_set(&pool->pages_nr, 0);
atomic64_set(&pool->unbuddied_nr, 0);
+ pool->compact_wq = create_singlethread_workqueue(pool->name);
+ if (!pool->compact_wq)
+ goto out;
+ INIT_DELAYED_WORK(&pool->work, z3fold_compact_work);
pool->ops = ops;
return pool;
+
+out:
+ if (pool)
+ kfree(pool);
+ return NULL;
}
/**
@@ -250,31 +381,11 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp,
*/
static void z3fold_destroy_pool(struct z3fold_pool *pool)
{
+ if (pool->compact_wq)
+ destroy_workqueue(pool->compact_wq);
kfree(pool);
}
-/* Has to be called with lock held */
-static int z3fold_compact_page(struct z3fold_header *zhdr)
-{
- struct page *page = virt_to_page(zhdr);
- void *beg = zhdr;
-
-
- if (!test_bit(MIDDLE_CHUNK_MAPPED, &page->private) &&
- zhdr->middle_chunks != 0 &&
- zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
- memmove(beg + ZHDR_SIZE_ALIGNED,
- beg + (zhdr->start_middle << CHUNK_SHIFT),
- zhdr->middle_chunks << CHUNK_SHIFT);
- zhdr->first_chunks = zhdr->middle_chunks;
- zhdr->middle_chunks = 0;
- zhdr->start_middle = 0;
- zhdr->first_num++;
- return 1;
- }
- return 0;
-}
-
/**
* z3fold_alloc() - allocates a region of a given size
* @pool: z3fold pool from which to allocate
@@ -464,11 +575,13 @@ static void z3fold_free(struct z3fold_pool *pool,
unsigned long handle)
free_z3fold_page(zhdr);
atomic64_dec(&pool->pages_nr);
} else {
- z3fold_compact_page(zhdr);
+ set_bit(COMPACTION_DEFERRED, &page->private);
/* Add to the unbuddied list */
freechunks = num_free_chunks(zhdr);
- list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+ list_add_tail(&zhdr->buddy, &pool->unbuddied[freechunks]);
atomic64_inc(&pool->unbuddied_nr);
+ if (!delayed_work_pending(&pool->work))
+ queue_delayed_work(pool->compact_wq, &pool->work, HZ);
}
write_unlock(&pool->lock);
@@ -596,7 +709,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool,
unsigned int retries)
/* Full, add to buddied list */
list_add(&zhdr->buddy, &pool->buddied);
} else {
- z3fold_compact_page(zhdr);
+ z3fold_compact_page(zhdr, true);
/* add to unbuddied list */
freechunks = num_free_chunks(zhdr);
list_add(&zhdr->buddy,
@@ -725,6 +838,7 @@ static void *z3fold_zpool_create(const char *name, gfp_t
gfp,
if (pool) {
pool->zpool = zpool;
pool->zpool_ops = zpool_ops;
+ pool->name = name;
}
return pool;
}
--
2.4.2
