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Date: Tue, 1 Nov 2016 18:16:07 -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 1/3] z3fold: make counters atomic
On Tue, Nov 1, 2016 at 5:03 PM, Vitaly Wool <vitalywool@...il.com> wrote:
> On Tue, Nov 1, 2016 at 9:03 PM, Dan Streetman <ddstreet@...e.org> wrote:
>> On Thu, Oct 27, 2016 at 7:08 AM, Vitaly Wool <vitalywool@...il.com> wrote:
>>> This patch converts pages_nr per-pool counter to atomic64_t.
>>> It also introduces a new counter, unbuddied_nr, which is
>>> atomic64_t, too, to track the number of unbuddied (compactable)
>>> z3fold pages.
>>
>> so, with the use of workqueues, do we still need the unbuddied_nr
>> counter? It doesn't seem to be used in later patches?
>
> I'm going to add sysfs/debugfs accounting a bit later so it won't rest unused.
>
> Also, with a per-page lock (if I come up with something reasonable) it could
> be still worth going back to shrinker.
let's wait to add it once the code that uses it is ready, yeah?
>
>> changing the pages_nr to atomic is a good idea though, so we can
>> safely read it without needing the pool lock.
>>
>>>
>>> Signed-off-by: Vitaly Wool <vitalywool@...il.com>
>>> ---
>>> mm/z3fold.c | 33 +++++++++++++++++++++++++--------
>>> 1 file changed, 25 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>>> index 8f9e89c..5ac325a 100644
>>> --- a/mm/z3fold.c
>>> +++ b/mm/z3fold.c
>>> @@ -69,6 +69,7 @@ struct z3fold_ops {
>>> * @lru: list tracking the z3fold pages in LRU order by most recently
>>> * added buddy.
>>> * @pages_nr: number of z3fold pages in the pool.
>>> + * @unbuddied_nr: number of unbuddied z3fold pages in the pool.
>>> * @ops: pointer to a structure of user defined operations specified at
>>> * pool creation time.
>>> *
>>> @@ -80,7 +81,8 @@ struct z3fold_pool {
>>> struct list_head unbuddied[NCHUNKS];
>>> struct list_head buddied;
>>> struct list_head lru;
>>> - u64 pages_nr;
>>> + atomic64_t pages_nr;
>>> + atomic64_t unbuddied_nr;
>>> const struct z3fold_ops *ops;
>>> struct zpool *zpool;
>>> const struct zpool_ops *zpool_ops;
>>> @@ -234,7 +236,8 @@ static struct z3fold_pool *z3fold_create_pool(gfp_t gfp,
>>> INIT_LIST_HEAD(&pool->unbuddied[i]);
>>> INIT_LIST_HEAD(&pool->buddied);
>>> INIT_LIST_HEAD(&pool->lru);
>>> - pool->pages_nr = 0;
>>> + atomic64_set(&pool->pages_nr, 0);
>>> + atomic64_set(&pool->unbuddied_nr, 0);
>>> pool->ops = ops;
>>> return pool;
>>> }
>>> @@ -334,6 +337,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
>>> continue;
>>> }
>>> list_del(&zhdr->buddy);
>>> + atomic64_dec(&pool->unbuddied_nr);
>>> goto found;
>>> }
>>> }
>>> @@ -346,7 +350,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
>>> if (!page)
>>> return -ENOMEM;
>>> spin_lock(&pool->lock);
>>> - pool->pages_nr++;
>>> + atomic64_inc(&pool->pages_nr);
>>> zhdr = init_z3fold_page(page);
>>>
>>> if (bud == HEADLESS) {
>>> @@ -369,6 +373,7 @@ 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]);
>>> + atomic64_inc(&pool->unbuddied_nr);
>>> } else {
>>> /* Add to buddied list */
>>> list_add(&zhdr->buddy, &pool->buddied);
>>> @@ -412,6 +417,10 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
>>> /* HEADLESS page stored */
>>> bud = HEADLESS;
>>> } else {
>>> + bool is_unbuddied = zhdr->first_chunks == 0 ||
>>> + zhdr->middle_chunks == 0 ||
>>> + zhdr->last_chunks == 0;
>>> +
>>> bud = handle_to_buddy(handle);
>>>
>>> switch (bud) {
>>> @@ -431,6 +440,8 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
>>> spin_unlock(&pool->lock);
>>> return;
>>> }
>>> + if (is_unbuddied)
>>> + atomic64_dec(&pool->unbuddied_nr);
>>> }
>>>
>>> if (test_bit(UNDER_RECLAIM, &page->private)) {
>>> @@ -451,12 +462,13 @@ 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);
>>> - pool->pages_nr--;
>>> + 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]);
>>> + atomic64_inc(&pool->unbuddied_nr);
>>> }
>>>
>>> spin_unlock(&pool->lock);
>>> @@ -520,6 +532,11 @@ 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);
>>> + if (zhdr->first_chunks == 0 ||
>>> + zhdr->middle_chunks == 0 ||
>>> + zhdr->last_chunks == 0)
>>> + atomic64_dec(&pool->unbuddied_nr);
>>> +
>>> /*
>>> * We need encode the handles before unlocking, since
>>> * we can race with free that will set
>>> @@ -569,7 +586,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>>> */
>>> clear_bit(PAGE_HEADLESS, &page->private);
>>> free_z3fold_page(zhdr);
>>> - pool->pages_nr--;
>>> + atomic64_dec(&pool->pages_nr);
>>> spin_unlock(&pool->lock);
>>> return 0;
>>> } else if (!test_bit(PAGE_HEADLESS, &page->private)) {
>>> @@ -584,6 +601,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>>> freechunks = num_free_chunks(zhdr);
>>> list_add(&zhdr->buddy,
>>> &pool->unbuddied[freechunks]);
>>> + atomic64_inc(&pool->unbuddied_nr);
>>> }
>>> }
>>>
>>> @@ -672,12 +690,11 @@ static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
>>> * z3fold_get_pool_size() - gets the z3fold pool size in pages
>>> * @pool: pool whose size is being queried
>>> *
>>> - * Returns: size in pages of the given pool. The pool lock need not be
>>> - * taken to access pages_nr.
>>> + * Returns: size in pages of the given pool.
>>> */
>>> static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
>>> {
>>> - return pool->pages_nr;
>>> + return atomic64_read(&pool->pages_nr);
>>> }
>>>
>>> /*****************
>>> --
>>> 2.4.2
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