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z3fold: use per-page spinlock
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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: Vitaly Wool <vitalywool@gmail.com>
Reviewed-by: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Vitaly Wool authored and Linus Torvalds committed Feb 25, 2017
1 parent 1b096e5 commit 2f1e5e4
Showing 1 changed file with 106 additions and 42 deletions.
148 changes: 106 additions & 42 deletions mm/z3fold.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,13 +51,15 @@ 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
* @first_num: the starting number (for the first handle)
*/
struct z3fold_header {
struct list_head buddy;
spinlock_t page_lock;
unsigned short first_chunks;
unsigned short middle_chunks;
unsigned short last_chunks;
Expand Down Expand Up @@ -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;
Expand All @@ -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
Expand Down Expand Up @@ -351,50 +367,60 @@ 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);
page = virt_to_page(zhdr);
if (zhdr->first_chunks == 0) {
if (zhdr->middle_chunks != 0 &&
chunks >= zhdr->start_middle)
bud = LAST;
else
bud = FIRST;
} else if (zhdr->last_chunks == 0)
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)
bud = LAST;
else if (zhdr->middle_chunks == 0)
bud = MIDDLE;
else {
pr_err("No free chunks in unbuddied\n");
WARN_ON(1);
continue;
}
list_del(&zhdr->buddy);
goto found;
else
bud = FIRST;
} else if (zhdr->last_chunks == 0)
bud = LAST;
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;
}
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)
Expand All @@ -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 */
Expand All @@ -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;
}
Expand All @@ -446,14 +475,14 @@ 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;
} else {
z3fold_page_lock(zhdr);
bud = handle_to_buddy(handle);

switch (bud) {
Expand All @@ -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)
list_del(&zhdr->buddy);
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);
}

/**
Expand Down Expand Up @@ -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);

Expand All @@ -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
Expand All @@ -575,13 +631,13 @@ 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);
}

spin_unlock(&pool->lock);

/* Issue the eviction callback(s) */
if (middle_handle) {
ret = pool->ops->evict(pool, middle_handle);
Expand All @@ -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 &&
Expand All @@ -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);
}
Expand All @@ -652,14 +717,14 @@ 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);

if (test_bit(PAGE_HEADLESS, &page->private))
goto out;

z3fold_page_lock(zhdr);
buddy = handle_to_buddy(handle);
switch (buddy) {
case FIRST:
Expand All @@ -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;
}

Expand All @@ -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);
}

/**
Expand Down

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