Re: [RFC PATCH 2/9] mm: zswap: refactor storing to the tree out of zswap_store()

[Chengming Zhou <chengming.zhou@linux.dev>]

On 2024/3/26 07:50, Yosry Ahmed wrote:
> Refactor the code that attempts storing to the xarray, handling erros,
> and freeing stale entries into a helper. This will be reused in a
> following patch to free other types of tree elements as well.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
> ---
>  mm/zswap.c | 42 ++++++++++++++++++++++++++----------------
>  1 file changed, 26 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 1cf3ab4b22e64..ff1975afb7e3d 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -827,6 +827,30 @@ static void zswap_entry_free(struct zswap_entry *entry)
>  	atomic_dec(&zswap_stored_pages);
>  }
>  
> +/*********************************
> +* zswap tree functions
> +**********************************/
> +static int zswap_tree_store(struct xarray *tree, pgoff_t offset, void *new)
> +{
> +	void *old;
> +	int err;
> +
> +	old = xa_store(tree, offset, new, GFP_KERNEL);
> +	err = xa_is_err(old);

Seems to use xa_err() to return errno, xa_is_err() just return a bool.

> +	if (err) {
> +		WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err);
> +		zswap_reject_alloc_fail++;
> +	} else if (old) {
> +		/*
> +		 * We may have had an existing entry that became stale when
> +		 * the folio was redirtied and now the new version is being
> +		 * swapped out. Get rid of the old.
> +		 */
> +		zswap_entry_free(old);
> +	}
> +	return err;
> +}
> +
>  /*********************************
>  * compressed storage functions
>  **********************************/
> @@ -1396,10 +1420,10 @@ bool zswap_store(struct folio *folio)
>  	swp_entry_t swp = folio->swap;
>  	pgoff_t offset = swp_offset(swp);
>  	struct xarray *tree = swap_zswap_tree(swp);
> -	struct zswap_entry *entry, *old;
>  	struct obj_cgroup *objcg = NULL;
>  	struct mem_cgroup *memcg = NULL;
>  	unsigned long max_pages, cur_pages;
> +	struct zswap_entry *entry;
>  
>  	VM_WARN_ON_ONCE(!folio_test_locked(folio));
>  	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
> @@ -1485,22 +1509,8 @@ bool zswap_store(struct folio *folio)
>  	entry->swpentry = swp;
>  	entry->objcg = objcg;
>  
> -	old = xa_store(tree, offset, entry, GFP_KERNEL);
> -	if (xa_is_err(old)) {
> -		int err = xa_err(old);
> -
> -		WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err);
> -		zswap_reject_alloc_fail++;
> +	if (zswap_tree_store(tree, offset, entry))
>  		goto store_failed;
> -	}
> -
> -	/*
> -	 * We may have had an existing entry that became stale when
> -	 * the folio was redirtied and now the new version is being
> -	 * swapped out. Get rid of the old.
> -	 */
> -	if (old)
> -		zswap_entry_free(old);
>  
>  	if (objcg) {
>  		obj_cgroup_charge_zswap(objcg, entry->length);