On Tue, Jul 07, 2015 at 08:57:01PM +0900, Sergey Senozhatsky wrote:
> Perform automatic pool compaction by a shrinker when system
> is getting tight on memory.
>
> User-space has a very little knowledge regarding zsmalloc fragmentation
> and basically has no mechanism to tell whether compaction will result
> in any memory gain. Another issue is that user space is not always
> aware of the fact that system is getting tight on memory. Which leads
> to very uncomfortable scenarios when user space may start issuing
> compaction 'randomly' or from crontab (for example). Fragmentation
> is not always necessarily bad, allocated and unused objects, after all,
> may be filled with the data later, w/o the need of allocating a new
> zspage. On the other hand, we obviously don't want to waste memory
> when the system needs it.
>
> Compaction now has a relatively quick pool scan so we are able to
> estimate the number of pages that will be freed easily, which makes it
> possible to call this function from a shrinker->count_objects() callback.
> We also abort compaction as soon as we detect that we can't free any
> pages any more, preventing wasteful objects migrations.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
There is one suggestion. Please see below.
> ---
> mm/zsmalloc.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 74 insertions(+)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 13f2c4a..83b2e97 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -247,6 +247,10 @@ struct zs_pool {
> atomic_long_t pages_allocated;
>
> struct zs_pool_stats stats;
> +
> + /* Compact classes */
> + struct shrinker shrinker;
> + bool shrinker_enabled;
> #ifdef CONFIG_ZSMALLOC_STAT
> struct dentry *stat_dentry;
> #endif
> @@ -1787,6 +1791,69 @@ void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats)
> }
> EXPORT_SYMBOL_GPL(zs_pool_stats);
>
> +static unsigned long zs_shrinker_scan(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + unsigned long pages_freed;
> + struct zs_pool *pool = container_of(shrinker, struct zs_pool,
> + shrinker);
> +
> + pages_freed = pool->stats.pages_compacted;
> + /*
> + * Compact classes and calculate compaction delta.
> + * Can run concurrently with a manually triggered
> + * (by user) compaction.
> + */
> + pages_freed = zs_compact(pool) - pages_freed;
> +
> + return pages_freed ? pages_freed : SHRINK_STOP;
> +}
> +
> +static unsigned long zs_shrinker_count(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + int i;
> + struct size_class *class;
> + unsigned long pages_to_free = 0;
> + struct zs_pool *pool = container_of(shrinker, struct zs_pool,
> + shrinker);
> +
> + if (!pool->shrinker_enabled)
> + return 0;
> +
> + for (i = zs_size_classes - 1; i >= 0; i--) {
> + class = pool->size_class[i];
> + if (!class)
> + continue;
> + if (class->index != i)
> + continue;
> +
> + spin_lock(&class->lock);
> + pages_to_free += zs_can_compact(class);
> + spin_unlock(&class->lock);
> + }
> +
> + return pages_to_free;
> +}
> +
> +static void zs_unregister_shrinker(struct zs_pool *pool)
> +{
> + if (pool->shrinker_enabled) {
> + unregister_shrinker(&pool->shrinker);
> + pool->shrinker_enabled = false;
> + }
> +}
> +
> +static int zs_register_shrinker(struct zs_pool *pool)
> +{
> + pool->shrinker.scan_objects = zs_shrinker_scan;
> + pool->shrinker.count_objects = zs_shrinker_count;
> + pool->shrinker.batch = 0;
> + pool->shrinker.seeks = DEFAULT_SEEKS;
> +
> + return register_shrinker(&pool->shrinker);
> +}
> +
> /**
> * zs_create_pool - Creates an allocation pool to work from.
> * @flags: allocation flags used to allocate pool metadata
> @@ -1872,6 +1939,12 @@ struct zs_pool *zs_create_pool(char *name, gfp_t flags)
> if (zs_pool_stat_create(name, pool))
> goto err;
>
> + /*
> + * Not critical, we still can use the pool
> + * and user can trigger compaction manually.
> + */
> + if (zs_register_shrinker(pool) == 0)
> + pool->shrinker_enabled = true;
IMO, there is no value to maintain just in case of
failing register_shrinker in practice.
Let's remove shrinker_enabled and abort pool creation if shrinker register
is failed.
Tomorrow, I will test this patchset and add Acked-by if it pass.
Thanks!
> return pool;
>
> err:
> @@ -1884,6 +1957,7 @@ void zs_destroy_pool(struct zs_pool *pool)
> {
> int i;
>
> + zs_unregister_shrinker(pool);
> zs_pool_stat_destroy(pool);
>
> for (i = 0; i < zs_size_classes; i++) {
> --
> 2.4.5
>
--
Kind regards,
Minchan Kim
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