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Date: Wed, 19 Oct 2016 18:35:57 +0200
From: Vitaly Wool <vitalywool@...il.com>
To: Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Cc: Dan Streetman <ddstreet@...e.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 2/3] z3fold: remove redundant locking
The per-pool z3fold spinlock should generally be taken only when
a non-atomic pool variable is modified. There's no need to take it
to map/unmap an object. This patch introduces per-page lock that
will be used instead to protect per-page variables in map/unmap
functions.
Signed-off-by: Vitaly Wool <vitalywool@...il.com>
---
mm/z3fold.c | 65 ++++++++++++++++++++++++++++++++++++-------------------------
1 file changed, 38 insertions(+), 27 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 5ac325a..329bc26 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -104,6 +104,7 @@ enum buddy {
* @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
* @first_num: the starting number (for the first handle)
+ * @page_lock: per-page lock
*/
struct z3fold_header {
struct list_head buddy;
@@ -112,6 +113,7 @@ struct z3fold_header {
unsigned short last_chunks;
unsigned short start_middle;
unsigned short first_num:NCHUNKS_ORDER;
+ raw_spinlock_t page_lock;
};
/*
@@ -152,6 +154,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page)
zhdr->first_num = 0;
zhdr->start_middle = 0;
INIT_LIST_HEAD(&zhdr->buddy);
+ raw_spin_lock_init(&zhdr->page_lock);
return zhdr;
}
@@ -163,15 +166,17 @@ static void free_z3fold_page(struct z3fold_header *zhdr)
/*
* Encodes the handle of a particular buddy within a z3fold page
- * Pool lock should be held as this function accesses first_num
*/
static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
{
unsigned long handle;
handle = (unsigned long)zhdr;
- if (bud != HEADLESS)
+ if (bud != HEADLESS) {
+ raw_spin_lock(&zhdr->page_lock);
handle += (bud + zhdr->first_num) & BUDDY_MASK;
+ raw_spin_unlock(&zhdr->page_lock);
+ }
return handle;
}
@@ -181,7 +186,10 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
return (struct z3fold_header *)(handle & PAGE_MASK);
}
-/* Returns buddy number */
+/*
+ * Returns buddy number.
+ * NB: can't be used with HEADLESS pages.
+ */
static enum buddy handle_to_buddy(unsigned long handle)
{
struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
@@ -253,7 +261,6 @@ static void z3fold_destroy_pool(struct z3fold_pool *pool)
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);
@@ -263,6 +270,7 @@ static int z3fold_compact_page(struct z3fold_header *zhdr)
if (!test_bit(MIDDLE_CHUNK_MAPPED, &page->private) &&
zhdr->middle_chunks != 0 &&
zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
+ raw_spin_lock(&zhdr->page_lock);
memmove(beg + ZHDR_SIZE_ALIGNED,
beg + (zhdr->start_middle << CHUNK_SHIFT),
zhdr->middle_chunks << CHUNK_SHIFT);
@@ -270,6 +278,7 @@ static int z3fold_compact_page(struct z3fold_header *zhdr)
zhdr->middle_chunks = 0;
zhdr->start_middle = 0;
zhdr->first_num++;
+ raw_spin_unlock(&zhdr->page_lock);
return 1;
}
return 0;
@@ -385,9 +394,9 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
list_del(&page->lru);
list_add(&page->lru, &pool->lru);
+ spin_unlock(&pool->lock);
*handle = encode_handle(zhdr, bud);
- spin_unlock(&pool->lock);
return 0;
}
@@ -409,15 +418,18 @@ 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);
if (test_bit(PAGE_HEADLESS, &page->private)) {
/* HEADLESS page stored */
bud = HEADLESS;
+ spin_lock(&pool->lock);
} else {
- bool is_unbuddied = zhdr->first_chunks == 0 ||
+ bool is_unbuddied;
+
+ raw_spin_lock(&zhdr->page_lock);
+ is_unbuddied = zhdr->first_chunks == 0 ||
zhdr->middle_chunks == 0 ||
zhdr->last_chunks == 0;
@@ -436,12 +448,17 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
break;
default:
pr_err("%s: unknown bud %d\n", __func__, bud);
+ raw_spin_unlock(&zhdr->page_lock);
WARN_ON(1);
- spin_unlock(&pool->lock);
return;
}
+ raw_spin_unlock(&zhdr->page_lock);
if (is_unbuddied)
atomic64_dec(&pool->unbuddied_nr);
+
+ spin_lock(&pool->lock);
+ /* Remove from existing buddy list */
+ list_del(&zhdr->buddy);
}
if (test_bit(UNDER_RECLAIM, &page->private)) {
@@ -450,11 +467,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
return;
}
- if (bud != HEADLESS) {
- /* Remove from existing buddy list */
- list_del(&zhdr->buddy);
- }
-
+ /* We've got the page and it is not under reclaim */
if (bud == HEADLESS ||
(zhdr->first_chunks == 0 && zhdr->middle_chunks == 0 &&
zhdr->last_chunks == 0)) {
@@ -462,16 +475,16 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
list_del(&page->lru);
clear_bit(PAGE_HEADLESS, &page->private);
free_z3fold_page(zhdr);
+ spin_unlock(&pool->lock);
atomic64_dec(&pool->pages_nr);
} else {
z3fold_compact_page(zhdr);
/* Add to the unbuddied list */
freechunks = num_free_chunks(zhdr);
list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+ spin_unlock(&pool->lock);
atomic64_inc(&pool->unbuddied_nr);
}
-
- spin_unlock(&pool->lock);
}
/**
@@ -580,6 +593,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
if ((test_bit(PAGE_HEADLESS, &page->private) && ret == 0) ||
(zhdr->first_chunks == 0 && zhdr->last_chunks == 0 &&
zhdr->middle_chunks == 0)) {
+ spin_unlock(&pool->lock);
/*
* All buddies are now free, free the z3fold page and
* return success.
@@ -587,7 +601,6 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
clear_bit(PAGE_HEADLESS, &page->private);
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 &&
@@ -629,7 +642,6 @@ 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);
@@ -637,7 +649,9 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
if (test_bit(PAGE_HEADLESS, &page->private))
goto out;
+ raw_spin_lock(&zhdr->page_lock);
buddy = handle_to_buddy(handle);
+
switch (buddy) {
case FIRST:
addr += ZHDR_SIZE_ALIGNED;
@@ -655,8 +669,8 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
addr = NULL;
break;
}
+ raw_spin_unlock(&zhdr->page_lock);
out:
- spin_unlock(&pool->lock);
return addr;
}
@@ -671,19 +685,16 @@ 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);
- return;
+ if (!test_bit(PAGE_HEADLESS, &page->private)) {
+ raw_spin_lock(&zhdr->page_lock);
+ buddy = handle_to_buddy(handle);
+ if (buddy == MIDDLE)
+ clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
+ raw_spin_unlock(&zhdr->page_lock);
}
-
- buddy = handle_to_buddy(handle);
- if (buddy == MIDDLE)
- clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
- spin_unlock(&pool->lock);
}
/**
--
2.4.2
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