linux-kernel - Re: [PATCH 1/3] z3fold: make counters atomic

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Date:   Sat, 22 Oct 2016 20:28:59 +0200
From:   Vitaly Wool <vitalywool@...il.com>
To:     Dan Streetman <ddstreet@...e.org>
Cc:     Linux-MM <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] z3fold: make counters atomic

On Thu, Oct 20, 2016 at 10:17 PM, Dan Streetman <ddstreet@...e.org> wrote:
> On Wed, Oct 19, 2016 at 12:35 PM, 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.
>>
>> 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);
>
> this should be below, where it's removed from its buddy list.  If it's
> under reclaim, it's already been removd from the buddy list and we
> shouldn't dec the counter.

Right, thanks. Will fix in the new respin.

~vitaly