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Date: Tue, 1 Nov 2016 16:16:40 -0400
From: Dan Streetman <ddstreet@...e.org>
To: Vitaly Wool <vitalywool@...il.com>
Cc: Linux-MM <linux-mm@...ck.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHv3 2/3] z3fold: change per-pool spinlock to rwlock
On Thu, Oct 27, 2016 at 7:12 AM, Vitaly Wool <vitalywool@...il.com> wrote:
> Mapping/unmapping goes with no actual modifications so it makes
> sense to only take a read lock in map/unmap functions.
>
> This change gives up to 10% performance gain and lower latencies
> in fio sequential read/write tests, e.g. before:
>
> Run status group 0 (all jobs):
> WRITE: io=2700.0GB, aggrb=3234.8MB/s, minb=276031KB/s, maxb=277391KB/s, mint=850530msec, maxt=854720msec
>
> Run status group 1 (all jobs):
> READ: io=2700.0GB, aggrb=4838.6MB/s, minb=412888KB/s, maxb=424969KB/s, mint=555168msec, maxt=571412msec
>
> after:
> Run status group 0 (all jobs):
> WRITE: io=2700.0GB, aggrb=3284.2MB/s, minb=280249KB/s, maxb=281130KB/s, mint=839218msec, maxt=841856msec
>
> Run status group 1 (all jobs):
> READ: io=2700.0GB, aggrb=5210.7MB/s, minb=444640KB/s, maxb=447791KB/s, mint=526874msec, maxt=530607msec
>
> Signed-off-by: Vitaly Wool <vitalywool@...il.com>
> ---
> mm/z3fold.c | 44 +++++++++++++++++++++++---------------------
> 1 file changed, 23 insertions(+), 21 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 5ac325a..014d84f 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -77,7 +77,7 @@ struct z3fold_ops {
> * pertaining to a particular z3fold pool.
> */
> struct z3fold_pool {
> - spinlock_t lock;
> + rwlock_t lock;
> struct list_head unbuddied[NCHUNKS];
> struct list_head buddied;
> struct list_head lru;
> @@ -231,7 +231,7 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp,
> pool = kzalloc(sizeof(struct z3fold_pool), gfp);
> if (!pool)
> return NULL;
> - spin_lock_init(&pool->lock);
> + rwlock_init(&pool->lock);
> for_each_unbuddied_list(i, 0)
> INIT_LIST_HEAD(&pool->unbuddied[i]);
> INIT_LIST_HEAD(&pool->buddied);
> @@ -312,7 +312,7 @@ 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);
> + write_lock(&pool->lock);
>
> /* First, try to find an unbuddied z3fold page. */
> zhdr = NULL;
> @@ -342,14 +342,14 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
> }
> }
> bud = FIRST;
> - spin_unlock(&pool->lock);
> + write_unlock(&pool->lock);
> }
>
> /* Couldn't find unbuddied z3fold page, create new one */
> page = alloc_page(gfp);
> if (!page)
> return -ENOMEM;
> - spin_lock(&pool->lock);
> + write_lock(&pool->lock);
> atomic64_inc(&pool->pages_nr);
> zhdr = init_z3fold_page(page);
>
> @@ -387,7 +387,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
> list_add(&page->lru, &pool->lru);
>
> *handle = encode_handle(zhdr, bud);
> - spin_unlock(&pool->lock);
> + write_unlock(&pool->lock);
>
> return 0;
> }
> @@ -409,7 +409,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
> struct page *page;
> enum buddy bud;
>
> - spin_lock(&pool->lock);
> + write_lock(&pool->lock);
> zhdr = handle_to_z3fold_header(handle);
> page = virt_to_page(zhdr);
>
> @@ -437,7 +437,7 @@ 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);
> + write_unlock(&pool->lock);
> return;
> }
> if (is_unbuddied)
> @@ -446,7 +446,7 @@ 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 */
> - spin_unlock(&pool->lock);
> + write_unlock(&pool->lock);
> return;
> }
>
> @@ -471,7 +471,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
> atomic64_inc(&pool->unbuddied_nr);
> }
>
> - spin_unlock(&pool->lock);
> + write_unlock(&pool->lock);
> }
>
> /**
> @@ -517,10 +517,10 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> struct page *page;
> unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
>
> - spin_lock(&pool->lock);
> + read_lock(&pool->lock);
this needs the write lock, as we actually change the pool's lists
inside the for loop below, e.g.:
page = list_last_entry(&pool->lru, struct page, lru);
list_del(&page->lru);
as well as:
list_del(&zhdr->buddy);
> if (!pool->ops || !pool->ops->evict || list_empty(&pool->lru) ||
> retries == 0) {
> - spin_unlock(&pool->lock);
> + read_unlock(&pool->lock);
> return -EINVAL;
> }
> for (i = 0; i < retries; i++) {
> @@ -556,7 +556,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> last_handle = middle_handle = 0;
> }
>
> - spin_unlock(&pool->lock);
> + read_unlock(&pool->lock);
>
> /* Issue the eviction callback(s) */
> if (middle_handle) {
> @@ -575,7 +575,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> goto next;
> }
> next:
> - spin_lock(&pool->lock);
> + write_lock(&pool->lock);
> clear_bit(UNDER_RECLAIM, &page->private);
> if ((test_bit(PAGE_HEADLESS, &page->private) && ret == 0) ||
> (zhdr->first_chunks == 0 && zhdr->last_chunks == 0 &&
> @@ -587,7 +587,7 @@ 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);
> + write_unlock(&pool->lock);
> return 0;
> } else if (!test_bit(PAGE_HEADLESS, &page->private)) {
> if (zhdr->first_chunks != 0 &&
> @@ -607,8 +607,10 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>
> /* add to beginning of LRU */
> list_add(&page->lru, &pool->lru);
> + write_unlock(&pool->lock);
> + read_lock(&pool->lock);
> }
> - spin_unlock(&pool->lock);
> + read_unlock(&pool->lock);
> return -EAGAIN;
> }
>
> @@ -629,7 +631,7 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
> void *addr;
> enum buddy buddy;
>
> - spin_lock(&pool->lock);
> + read_lock(&pool->lock);
> zhdr = handle_to_z3fold_header(handle);
> addr = zhdr;
> page = virt_to_page(zhdr);
> @@ -656,7 +658,7 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
> break;
> }
> out:
> - spin_unlock(&pool->lock);
> + read_unlock(&pool->lock);
> return addr;
> }
>
> @@ -671,19 +673,19 @@ static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
> struct page *page;
> enum buddy buddy;
>
> - spin_lock(&pool->lock);
> + read_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);
> + read_unlock(&pool->lock);
> return;
> }
>
> buddy = handle_to_buddy(handle);
> if (buddy == MIDDLE)
> clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
> - spin_unlock(&pool->lock);
> + read_unlock(&pool->lock);
> }
>
> /**
> --
> 2.4.2
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