Commit 5a27aa82 authored by Vitaly Wool's avatar Vitaly Wool Committed by Linus Torvalds
Browse files

z3fold: add kref refcounting 

With both coming and already present locking optimizations, introducing
kref to reference-count z3fold objects is the right thing to do.
Moreover, it makes buddied list no longer necessary, and allows for a
simpler handling of headless pages.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170131214650.8ea78033d91ded233f552bc0@gmail.com


Signed-off-by: default avatarVitaly Wool <vitalywool@gmail.com>
Reviewed-by: default avatarDan Streetman <ddstreet@ieee.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2f1e5e4d

mm/z3fold.c

+69 −86
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ enum buddy { 
 *			z3fold page, except for HEADLESS pages

 * @buddy:	links the z3fold page into the relevant list in the pool

 * @page_lock:		per-page lock

 * @refcount:		reference cound for the z3fold page

 * @first_chunks:	the size of the first buddy in chunks, 0 if free

 * @middle_chunks:	the size of the middle buddy in chunks, 0 if free

 * @last_chunks:	the size of the last buddy in chunks, 0 if free
@@ -60,6 +61,7 @@ enum buddy { 
struct z3fold_header {

	struct list_head buddy;

	spinlock_t page_lock;

	struct kref refcount;

	unsigned short first_chunks;

	unsigned short middle_chunks;

	unsigned short last_chunks;
@@ -95,8 +97,6 @@ struct z3fold_header { 
 * @unbuddied:	array of lists tracking z3fold pages that contain 2- buddies;

 *		the lists each z3fold page is added to depends on the size of

 *		its free region.

 * @buddied:	list tracking the z3fold pages that contain 3 buddies;

 *		these z3fold pages are full

 * @lru:	list tracking the z3fold pages in LRU order by most recently

 *		added buddy.

 * @pages_nr:	number of z3fold pages in the pool.
@@ -109,7 +109,6 @@ struct z3fold_header { 
struct z3fold_pool {

	spinlock_t lock;

	struct list_head unbuddied[NCHUNKS];

	struct list_head buddied;

	struct list_head lru;

	atomic64_t pages_nr;

	const struct z3fold_ops *ops;
@@ -121,8 +120,7 @@ struct z3fold_pool { 
 * Internal z3fold page flags

 */

enum z3fold_page_flags {

	UNDER_RECLAIM = 0,

	PAGE_HEADLESS,

	PAGE_HEADLESS = 0,

	MIDDLE_CHUNK_MAPPED,

};
@@ -146,11 +144,11 @@ static struct z3fold_header *init_z3fold_page(struct page *page) 
	struct z3fold_header *zhdr = page_address(page);



	INIT_LIST_HEAD(&page->lru);

	clear_bit(UNDER_RECLAIM, &page->private);

	clear_bit(PAGE_HEADLESS, &page->private);

	clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);



	spin_lock_init(&zhdr->page_lock);

	kref_init(&zhdr->refcount);

	zhdr->first_chunks = 0;

	zhdr->middle_chunks = 0;

	zhdr->last_chunks = 0;
@@ -161,9 +159,24 @@ static struct z3fold_header *init_z3fold_page(struct page *page) 
}



/* Resets the struct page fields and frees the page */

static void free_z3fold_page(struct z3fold_header *zhdr)

static void free_z3fold_page(struct page *page)

{

	__free_page(virt_to_page(zhdr));

	__free_page(page);

}



static void release_z3fold_page(struct kref *ref)

{

	struct z3fold_header *zhdr;

	struct page *page;



	zhdr = container_of(ref, struct z3fold_header, refcount);

	page = virt_to_page(zhdr);



	if (!list_empty(&zhdr->buddy))

		list_del(&zhdr->buddy);

	if (!list_empty(&page->lru))

		list_del(&page->lru);

	free_z3fold_page(page);

}



/* Lock a z3fold page */
@@ -178,7 +191,6 @@ static inline void z3fold_page_unlock(struct z3fold_header *zhdr) 
	spin_unlock(&zhdr->page_lock);

}





/*

 * Encodes the handle of a particular buddy within a z3fold page

 * Pool lock should be held as this function accesses first_num
@@ -257,7 +269,6 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp, 
	spin_lock_init(&pool->lock);

	for_each_unbuddied_list(i, 0)

		INIT_LIST_HEAD(&pool->unbuddied[i]);

	INIT_LIST_HEAD(&pool->buddied);

	INIT_LIST_HEAD(&pool->lru);

	atomic64_set(&pool->pages_nr, 0);

	pool->ops = ops;
@@ -378,6 +389,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, 
				spin_unlock(&pool->lock);

				continue;

			}

			kref_get(&zhdr->refcount);

			list_del_init(&zhdr->buddy);

			spin_unlock(&pool->lock);
@@ -394,10 +406,12 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, 
			else if (zhdr->middle_chunks == 0)

				bud = MIDDLE;

			else {

				z3fold_page_unlock(zhdr);

				spin_lock(&pool->lock);

				list_add(&zhdr->buddy, &pool->buddied);

				if (kref_put(&zhdr->refcount,

					     release_z3fold_page))

					atomic64_dec(&pool->pages_nr);

				spin_unlock(&pool->lock);

				z3fold_page_unlock(zhdr);

				pr_err("No free chunks in unbuddied\n");

				WARN_ON(1);

				continue;
@@ -438,9 +452,6 @@ found: 
		/* Add to unbuddied list */

		freechunks = num_free_chunks(zhdr);

		list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);

	} else {

		/* Add to buddied list */

		list_add(&zhdr->buddy, &pool->buddied);

	}



headless:
@@ -504,52 +515,29 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle) 
		}

	}



	if (test_bit(UNDER_RECLAIM, &page->private)) {

		/* z3fold page is under reclaim, reclaim will free */

		if (bud != HEADLESS)

			z3fold_page_unlock(zhdr);

		return;

	}



	/* Remove from existing buddy list */

	if (bud != HEADLESS) {

		spin_lock(&pool->lock);

		/*

		 * this object may have been removed from its list by

		 * z3fold_alloc(). In that case we just do nothing,

		 * z3fold_alloc() will allocate an object and add the page

		 * to the relevant list.

		 */

		if (!list_empty(&zhdr->buddy)) {

			list_del(&zhdr->buddy);

		} else {

			spin_unlock(&pool->lock);

			z3fold_page_unlock(zhdr);

			return;

		}

		spin_unlock(&pool->lock);

	}



	if (bud == HEADLESS ||

	    (zhdr->first_chunks == 0 && zhdr->middle_chunks == 0 &&

			zhdr->last_chunks == 0)) {

		/* z3fold page is empty, free */

	if (bud == HEADLESS) {

		spin_lock(&pool->lock);

		list_del(&page->lru);

		spin_unlock(&pool->lock);

		clear_bit(PAGE_HEADLESS, &page->private);

		if (bud != HEADLESS)

			z3fold_page_unlock(zhdr);

		free_z3fold_page(zhdr);

		free_z3fold_page(page);

		atomic64_dec(&pool->pages_nr);

	} else {

		if (zhdr->first_chunks != 0 || zhdr->middle_chunks != 0 ||

		    zhdr->last_chunks != 0) {

			z3fold_compact_page(zhdr);

			/* Add to the unbuddied list */

			spin_lock(&pool->lock);

			if (!list_empty(&zhdr->buddy))

				list_del(&zhdr->buddy);

			freechunks = num_free_chunks(zhdr);

			list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);

			spin_unlock(&pool->lock);

		}

		z3fold_page_unlock(zhdr);

		spin_lock(&pool->lock);

		if (kref_put(&zhdr->refcount, release_z3fold_page))

			atomic64_dec(&pool->pages_nr);

		spin_unlock(&pool->lock);

	}



}
@@ -608,13 +596,13 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) 
			return -EINVAL;

		}

		page = list_last_entry(&pool->lru, struct page, lru);

		list_del(&page->lru);

		list_del_init(&page->lru);



		/* Protect z3fold page against free */

		set_bit(UNDER_RECLAIM, &page->private);

		zhdr = page_address(page);

		if (!test_bit(PAGE_HEADLESS, &page->private)) {

			list_del(&zhdr->buddy);

			if (!list_empty(&zhdr->buddy))

				list_del_init(&zhdr->buddy);

			kref_get(&zhdr->refcount);

			spin_unlock(&pool->lock);

			z3fold_page_lock(zhdr);

			/*
@@ -655,30 +643,19 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) 
				goto next;

		}

next:

		if (!test_bit(PAGE_HEADLESS, &page->private))

			z3fold_page_lock(zhdr);

		clear_bit(UNDER_RECLAIM, &page->private);

		if ((test_bit(PAGE_HEADLESS, &page->private) && ret == 0) ||

		    (zhdr->first_chunks == 0 && zhdr->last_chunks == 0 &&

		     zhdr->middle_chunks == 0)) {

			/*

			 * All buddies are now free, free the z3fold page and

			 * return success.

			 */

			if (!test_and_clear_bit(PAGE_HEADLESS, &page->private))

				z3fold_page_unlock(zhdr);

			free_z3fold_page(zhdr);

			atomic64_dec(&pool->pages_nr);

		if (test_bit(PAGE_HEADLESS, &page->private)) {

			if (ret == 0) {

				free_z3fold_page(page);

				return 0;

		}  else if (!test_bit(PAGE_HEADLESS, &page->private)) {

			if (zhdr->first_chunks != 0 &&

			    zhdr->last_chunks != 0 &&

			    zhdr->middle_chunks != 0) {

				/* Full, add to buddied list */

			} else {

				spin_lock(&pool->lock);

				list_add(&zhdr->buddy, &pool->buddied);

				spin_unlock(&pool->lock);

			}

		} else {

			z3fold_page_lock(zhdr);

			if ((zhdr->first_chunks || zhdr->last_chunks ||

			     zhdr->middle_chunks) &&

			    !(zhdr->first_chunks && zhdr->last_chunks &&

			      zhdr->middle_chunks)) {

				z3fold_compact_page(zhdr);

				/* add to unbuddied list */

				spin_lock(&pool->lock);
@@ -687,13 +664,19 @@ next: 
					 &pool->unbuddied[freechunks]);

				spin_unlock(&pool->lock);

			}

		}



		if (!test_bit(PAGE_HEADLESS, &page->private))

			z3fold_page_unlock(zhdr);



			spin_lock(&pool->lock);

		/* add to beginning of LRU */

			if (kref_put(&zhdr->refcount, release_z3fold_page)) {

				atomic64_dec(&pool->pages_nr);

				return 0;

			}

		}



		/*

		 * Add to the beginning of LRU.

		 * Pool lock has to be kept here to ensure the page has

		 * not already been released

		 */

		list_add(&page->lru, &pool->lru);

	}

	spin_unlock(&pool->lock);

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