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Commit 2f1e5e4d authored by Vitaly Wool's avatar Vitaly Wool Committed by Linus Torvalds
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z3fold: use per-page spinlock 

Most of z3fold operations are in-page, such as modifying z3fold page
header or moving z3fold objects within a page.  Taking per-pool spinlock
to protect per-page objects is therefore suboptimal, and the idea of
having a per-page spinlock (or rwlock) has been around for some time.

This patch implements spinlock-based per-page locking mechanism which is
lightweight enough to normally fit ok into the z3fold header.

Link: http://lkml.kernel.org/r/20170131214438.433e0a5fda908337b63206d3@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 1b096e5a

mm/z3fold.c

+106 −42
Original line number Diff line number Diff line
@@ -51,6 +51,7 @@ enum buddy { 
 * struct z3fold_header - z3fold page metadata occupying the first chunk of each

 *			z3fold page, except for HEADLESS pages

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

 * @page_lock:		per-page lock

 * @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
@@ -58,6 +59,7 @@ enum buddy { 
 */

struct z3fold_header {

	struct list_head buddy;

	spinlock_t page_lock;

	unsigned short first_chunks;

	unsigned short middle_chunks;

	unsigned short last_chunks;
@@ -148,6 +150,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page) 
	clear_bit(PAGE_HEADLESS, &page->private);

	clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);



	spin_lock_init(&zhdr->page_lock);

	zhdr->first_chunks = 0;

	zhdr->middle_chunks = 0;

	zhdr->last_chunks = 0;
@@ -163,6 +166,19 @@ static void free_z3fold_page(struct z3fold_header *zhdr) 
	__free_page(virt_to_page(zhdr));

}



/* Lock a z3fold page */

static inline void z3fold_page_lock(struct z3fold_header *zhdr)

{

	spin_lock(&zhdr->page_lock);

}



/* Unlock a z3fold page */

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
@@ -351,15 +367,22 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, 
		bud = HEADLESS;

	else {

		chunks = size_to_chunks(size);

		spin_lock(&pool->lock);



		/* First, try to find an unbuddied z3fold page. */

		zhdr = NULL;

		for_each_unbuddied_list(i, chunks) {

			if (!list_empty(&pool->unbuddied[i])) {

				zhdr = list_first_entry(&pool->unbuddied[i],

			spin_lock(&pool->lock);

			zhdr = list_first_entry_or_null(&pool->unbuddied[i],

						struct z3fold_header, buddy);

			if (!zhdr) {

				spin_unlock(&pool->lock);

				continue;

			}

			list_del_init(&zhdr->buddy);

			spin_unlock(&pool->lock);



			page = virt_to_page(zhdr);

			z3fold_page_lock(zhdr);

			if (zhdr->first_chunks == 0) {

				if (zhdr->middle_chunks != 0 &&

				    chunks >= zhdr->start_middle)
@@ -371,30 +394,33 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, 
			else if (zhdr->middle_chunks == 0)

				bud = MIDDLE;

			else {

				spin_lock(&pool->lock);

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

				spin_unlock(&pool->lock);

				z3fold_page_unlock(zhdr);

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

				WARN_ON(1);

				continue;

			}

				list_del(&zhdr->buddy);

			goto found;

		}

		}

		bud = FIRST;

		spin_unlock(&pool->lock);

	}



	/* Couldn't find unbuddied z3fold page, create new one */

	page = alloc_page(gfp);

	if (!page)

		return -ENOMEM;

	spin_lock(&pool->lock);



	atomic64_inc(&pool->pages_nr);

	zhdr = init_z3fold_page(page);



	if (bud == HEADLESS) {

		set_bit(PAGE_HEADLESS, &page->private);

		spin_lock(&pool->lock);

		goto headless;

	}

	z3fold_page_lock(zhdr);



found:

	if (bud == FIRST)
@@ -406,6 +432,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, 
		zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;

	}



	spin_lock(&pool->lock);

	if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||

			zhdr->middle_chunks == 0) {

		/* Add to unbuddied list */
@@ -425,6 +452,8 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, 


	*handle = encode_handle(zhdr, bud);

	spin_unlock(&pool->lock);

	if (bud != HEADLESS)

		z3fold_page_unlock(zhdr);



	return 0;

}
@@ -446,7 +475,6 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle) 
	struct page *page;

	enum buddy bud;



	spin_lock(&pool->lock);

	zhdr = handle_to_z3fold_header(handle);

	page = virt_to_page(zhdr);
@@ -454,6 +482,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle) 
		/* HEADLESS page stored */

		bud = HEADLESS;

	} else {

		z3fold_page_lock(zhdr);

		bud = handle_to_buddy(handle);



		switch (bud) {
@@ -470,37 +499,59 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle) 
		default:

			pr_err("%s: unknown bud %d\n", __func__, bud);

			WARN_ON(1);

			spin_unlock(&pool->lock);

			z3fold_page_unlock(zhdr);

			return;

		}

	}



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

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

		spin_unlock(&pool->lock);

		if (bud != HEADLESS)

			z3fold_page_unlock(zhdr);

		return;

	}



	/* Remove from existing buddy list */

	if (bud != HEADLESS)

	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 */

		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);

		atomic64_dec(&pool->pages_nr);

	} else {

		z3fold_compact_page(zhdr);

		/* Add to the unbuddied list */

		spin_lock(&pool->lock);

		freechunks = num_free_chunks(zhdr);

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

		spin_unlock(&pool->lock);

		z3fold_page_unlock(zhdr);

	}



	spin_unlock(&pool->lock);

}



/**
@@ -547,12 +598,15 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) 
	unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;



	spin_lock(&pool->lock);

	if (!pool->ops || !pool->ops->evict || list_empty(&pool->lru) ||

			retries == 0) {

	if (!pool->ops || !pool->ops->evict || retries == 0) {

		spin_unlock(&pool->lock);

		return -EINVAL;

	}

	for (i = 0; i < retries; i++) {

		if (list_empty(&pool->lru)) {

			spin_unlock(&pool->lock);

			return -EINVAL;

		}

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

		list_del(&page->lru);
@@ -561,6 +615,8 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) 
		zhdr = page_address(page);

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

			list_del(&zhdr->buddy);

			spin_unlock(&pool->lock);

			z3fold_page_lock(zhdr);

			/*

			 * We need encode the handles before unlocking, since

			 * we can race with free that will set
@@ -575,12 +631,12 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) 
				middle_handle = encode_handle(zhdr, MIDDLE);

			if (zhdr->last_chunks)

				last_handle = encode_handle(zhdr, LAST);

			z3fold_page_unlock(zhdr);

		} else {

			first_handle = encode_handle(zhdr, HEADLESS);

			last_handle = middle_handle = 0;

		}



			spin_unlock(&pool->lock);

		}



		/* Issue the eviction callback(s) */

		if (middle_handle) {
@@ -599,7 +655,8 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) 
				goto next;

		}

next:

		spin_lock(&pool->lock);

		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 &&
@@ -608,26 +665,34 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) 
			 * All buddies are now free, free the z3fold page and

			 * return success.

			 */

			clear_bit(PAGE_HEADLESS, &page->private);

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

				z3fold_page_unlock(zhdr);

			free_z3fold_page(zhdr);

			atomic64_dec(&pool->pages_nr);

			spin_unlock(&pool->lock);

			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 */

				spin_lock(&pool->lock);

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

				spin_unlock(&pool->lock);

			} else {

				z3fold_compact_page(zhdr);

				/* add to unbuddied list */

				spin_lock(&pool->lock);

				freechunks = num_free_chunks(zhdr);

				list_add(&zhdr->buddy,

					 &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 */

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

	}
@@ -652,7 +717,6 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle) 
	void *addr;

	enum buddy buddy;



	spin_lock(&pool->lock);

	zhdr = handle_to_z3fold_header(handle);

	addr = zhdr;

	page = virt_to_page(zhdr);
@@ -660,6 +724,7 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle) 
	if (test_bit(PAGE_HEADLESS, &page->private))

		goto out;



	z3fold_page_lock(zhdr);

	buddy = handle_to_buddy(handle);

	switch (buddy) {

	case FIRST:
@@ -678,8 +743,9 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle) 
		addr = NULL;

		break;

	}



	z3fold_page_unlock(zhdr);

out:

	spin_unlock(&pool->lock);

	return addr;

}
@@ -694,19 +760,17 @@ static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle) 
	struct page *page;

	enum buddy buddy;



	spin_lock(&pool->lock);

	zhdr = handle_to_z3fold_header(handle);

	page = virt_to_page(zhdr);



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

		spin_unlock(&pool->lock);

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

		return;

	}



	z3fold_page_lock(zhdr);

	buddy = handle_to_buddy(handle);

	if (buddy == MIDDLE)

		clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);

	spin_unlock(&pool->lock);

	z3fold_page_unlock(zhdr);

}



/**