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SubjectRe: [PATCH v5 1/3] z3fold: make counters atomic
On Sat, Oct 15, 2016 at 7:58 AM, Vitaly Wool <vitalywool@gmail.com> wrote:
> This patch converts pages_nr per-pool counter to atomic64_t.
> It also introduces a new counter, unbuddied_nr, which is also
> atomic64_t, to track the number of unbuddied (shrinkable) pages,
> as a step to prepare for z3fold shrinker implementation.
>
> Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
> ---
> mm/z3fold.c | 33 +++++++++++++++++++++++++--------
> 1 file changed, 25 insertions(+), 8 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 8f9e89c..5197d7b 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 @@ found:
> /* 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 +417,11 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
> /* HEADLESS page stored */
> bud = HEADLESS;
> } else {
> + if (zhdr->first_chunks == 0 ||
> + zhdr->middle_chunks == 0 ||
> + zhdr->last_chunks == 0)
> + atomic64_dec(&pool->unbuddied_nr);
> +
> bud = handle_to_buddy(handle);
>
> switch (bud) {
> @@ -429,6 +439,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
> pr_err("%s: unknown bud %d\n", __func__, bud);
> WARN_ON(1);
> spin_unlock(&pool->lock);
> + atomic64_inc(&pool->unbuddied_nr);

this is wrong if the page was fully buddied; instead it may be better
to set a flag above, e.g. is_unbuddied, and later at the list_del call
do the dec if is_unbuddied. That avoids needing to do this inc.

otherwise,

Acked-by: Dan Streetman <ddstreet@ieee.org>

> return;
> }
> }
> @@ -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 @@ next:
> */
> 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 @@ next:
> 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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