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Message-Id: <20161226014059.d1aa11c9ed4ac3380bd35870@gmail.com>
Date: Mon, 26 Dec 2016 01:40:59 +0100
From: Vitaly Wool <vitalywool@...il.com>
To: Vitaly Wool <vitalywool@...il.com>
Cc: Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
Dan Streetman <ddstreet@...e.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH/RESEND 5/5] 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.
Signed-off-by: Vitaly Wool <vitalywool@...il.com>
---
mm/z3fold.c | 137 ++++++++++++++++++++++++++++++------------------------------
1 file changed, 68 insertions(+), 69 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 729a2da..4593493 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -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;
raw_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;
@@ -162,9 +161,21 @@ 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 = container_of(ref, struct z3fold_header,
+ refcount);
+ struct page *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 */
@@ -256,9 +267,9 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp,
if (!pool)
return NULL;
spin_lock_init(&pool->lock);
+ kref_init(&zhdr->refcount);
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;
@@ -383,7 +394,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
spin_lock(&pool->lock);
zhdr = list_first_entry_or_null(&pool->unbuddied[i],
struct z3fold_header, buddy);
- if (!zhdr) {
+ if (!zhdr || !kref_get_unless_zero(&zhdr->refcount)) {
spin_unlock(&pool->lock);
continue;
}
@@ -403,10 +414,12 @@ 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;
@@ -447,9 +460,6 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
/* 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:
@@ -515,50 +525,39 @@ 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)
+ 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_lock(&pool->lock);
+ if (kref_put(&zhdr->refcount, release_z3fold_page))
+ atomic64_dec(&pool->pages_nr);
spin_unlock(&pool->lock);
- z3fold_page_unlock(zhdr);
- return;
}
- spin_unlock(&pool->lock);
+ return;
}
- 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 {
- z3fold_compact_page(zhdr);
- /* Add to the unbuddied list */
+ 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);
- freechunks = num_free_chunks(zhdr);
- list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+ if (kref_put(&zhdr->refcount, release_z3fold_page))
+ atomic64_dec(&pool->pages_nr);
spin_unlock(&pool->lock);
- z3fold_page_unlock(zhdr);
}
}
@@ -617,13 +616,15 @@ 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);
/*
@@ -664,30 +665,26 @@ 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))
+ if (test_bit(PAGE_HEADLESS, &page->private)) {
+ if (ret == 0) {
+ free_z3fold_page(page);
+ return 0;
+ }
+ } else {
+ z3fold_page_lock(zhdr);
+ if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0 &&
+ zhdr->middle_chunks == 0) {
z3fold_page_unlock(zhdr);
- free_z3fold_page(zhdr);
- atomic64_dec(&pool->pages_nr);
- 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);
+ if (kref_put(&zhdr->refcount,
+ release_z3fold_page))
+ atomic64_dec(&pool->pages_nr);
spin_unlock(&pool->lock);
- } else {
+ return 0;
+ } else if (zhdr->first_chunks == 0 ||
+ zhdr->last_chunks == 0 ||
+ zhdr->middle_chunks == 0) {
z3fold_compact_page(zhdr);
/* add to unbuddied list */
spin_lock(&pool->lock);
@@ -696,10 +693,12 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
&pool->unbuddied[freechunks]);
spin_unlock(&pool->lock);
}
- }
-
- if (!test_bit(PAGE_HEADLESS, &page->private))
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);
+ }
spin_lock(&pool->lock);
/* add to beginning of LRU */
--
2.4.2
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