Re: [PATCH v5 6/6] zsmalloc: Implement writeback mechanism for zsmalloc

[Minchan Kim <minchan@kernel.org>]

On Fri, Nov 18, 2022 at 10:24:07AM -0800, Nhat Pham wrote:
> This commit adds the writeback mechanism for zsmalloc, analogous to the
> zbud allocator. Zsmalloc will attempt to determine the coldest zspage
> (i.e least recently used) in the pool, and attempt to write back all the
> stored compressed objects via the pool's evict handler.
> 
> Signed-off-by: Nhat Pham <nphamcs@gmail.com>
> ---
>  mm/zsmalloc.c | 193 +++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 182 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 3ff86f57d08c..d73b9f9e9adf 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -271,12 +271,13 @@ struct zspage {
>  #ifdef CONFIG_ZPOOL
>  	/* links the zspage to the lru list in the pool */
>  	struct list_head lru;
> +	bool under_reclaim;
> +	/* list of unfreed handles whose objects have been reclaimed */
> +	unsigned long *deferred_handles;
>  #endif
> 
>  	struct zs_pool *pool;
> -#ifdef CONFIG_COMPACTION
>  	rwlock_t lock;
> -#endif
>  };
> 
>  struct mapping_area {
> @@ -297,10 +298,11 @@ static bool ZsHugePage(struct zspage *zspage)
>  	return zspage->huge;
>  }
> 
> -#ifdef CONFIG_COMPACTION
>  static void migrate_lock_init(struct zspage *zspage);
>  static void migrate_read_lock(struct zspage *zspage);
>  static void migrate_read_unlock(struct zspage *zspage);
> +
> +#ifdef CONFIG_COMPACTION
>  static void migrate_write_lock(struct zspage *zspage);
>  static void migrate_write_lock_nested(struct zspage *zspage);
>  static void migrate_write_unlock(struct zspage *zspage);
> @@ -308,9 +310,6 @@ static void kick_deferred_free(struct zs_pool *pool);
>  static void init_deferred_free(struct zs_pool *pool);
>  static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage);
>  #else
> -static void migrate_lock_init(struct zspage *zspage) {}
> -static void migrate_read_lock(struct zspage *zspage) {}
> -static void migrate_read_unlock(struct zspage *zspage) {}
>  static void migrate_write_lock(struct zspage *zspage) {}
>  static void migrate_write_lock_nested(struct zspage *zspage) {}
>  static void migrate_write_unlock(struct zspage *zspage) {}
> @@ -425,6 +424,27 @@ static void zs_zpool_free(void *pool, unsigned long handle)
>  	zs_free(pool, handle);
>  }
> 
> +static int zs_reclaim_page(struct zs_pool *pool, unsigned int retries);
> +
> +static int zs_zpool_shrink(void *pool, unsigned int pages,
> +			unsigned int *reclaimed)
> +{
> +	unsigned int total = 0;
> +	int ret = -EINVAL;
> +
> +	while (total < pages) {
> +		ret = zs_reclaim_page(pool, 8);
> +		if (ret < 0)
> +			break;
> +		total++;
> +	}
> +
> +	if (reclaimed)
> +		*reclaimed = total;
> +
> +	return ret;
> +}
> +
>  static void *zs_zpool_map(void *pool, unsigned long handle,
>  			enum zpool_mapmode mm)
>  {
> @@ -463,6 +483,7 @@ static struct zpool_driver zs_zpool_driver = {
>  	.malloc_support_movable = true,
>  	.malloc =		  zs_zpool_malloc,
>  	.free =			  zs_zpool_free,
> +	.shrink =		  zs_zpool_shrink,
>  	.map =			  zs_zpool_map,
>  	.unmap =		  zs_zpool_unmap,
>  	.total_size =		  zs_zpool_total_size,
> @@ -936,6 +957,23 @@ static int trylock_zspage(struct zspage *zspage)
>  	return 0;
>  }
> 
> +#ifdef CONFIG_ZPOOL
> +/*
> + * Free all the deferred handles whose objects are freed in zs_free.
> + */
> +static void free_handles(struct zs_pool *pool, struct zspage *zspage)
> +{
> +	unsigned long handle = (unsigned long)zspage->deferred_handles;
> +
> +	while (handle) {
> +		unsigned long nxt_handle = handle_to_obj(handle);
> +
> +		cache_free_handle(pool, handle);
> +		handle = nxt_handle;
> +	}
> +}

# else 

 static inline void free_handles(struct zs_pool *pool, struct zspage *zspage) {}

> +#endif
> +
>  static void __free_zspage(struct zs_pool *pool, struct size_class *class,
>  				struct zspage *zspage)
>  {
> @@ -950,6 +988,11 @@ static void __free_zspage(struct zs_pool *pool, struct size_class *class,
>  	VM_BUG_ON(get_zspage_inuse(zspage));
>  	VM_BUG_ON(fg != ZS_EMPTY);
> 
> +#ifdef CONFIG_ZPOOL

Let's remove the ifdef machinery here.

> +	/* Free all deferred handles from zs_free */
> +	free_handles(pool, zspage);
> +#endif
> +

Other than that, looks good to me.