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

Chengming Zhou
2024-03-27T02:25:40Z

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);