Re: [PATCH -next] mm: zswap: update comment for struct zswap_entry

[Yosry Ahmed <yosryahmed@google.com>]

Hi Xiu,

On Mon, Aug 7, 2023 at 7:49 PM Xiu Jianfeng <xiujianfeng@huaweicloud.com> wrote:
>
> From: Xiu Jianfeng <xiujianfeng@huawei.com>
>
> Since commit 0bb488498c98 ("mm: zswap: remove zswap_header"), the
> 'offset' has been replaced by swpentry, update the comment for it,
> and also add comment for 'objcg'.
>
> Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
> ---
>  mm/zswap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 5b56d38e7339..d7863c139c82 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -182,7 +182,7 @@ struct zswap_pool {
>   * page within zswap.
>   *
>   * rbnode - links the entry into red-black tree for the appropriate swap type
> - * offset - the swap offset for the entry.  Index into the red-black tree.
> + * swpentry - the swap entry for the entry, include 'type' and 'offset' fields


This is not the place to document that a swap entry has 'type' and
'offset' fields.

I would also avoid the repetitive 'entry'. Maybe something like:
swpentry - associated swap entry, the offset indexes into the red-black tree

>
>   * refcount - the number of outstanding reference to the entry. This is needed
>   *            to protect against premature freeing of the entry by code
>   *            concurrent calls to load, invalidate, and writeback.  The lock
> @@ -195,6 +195,7 @@ struct zswap_pool {
>   * pool - the zswap_pool the entry's data is in
>   * handle - zpool allocation handle that stores the compressed page data
>   * value - value of the same-value filled pages which have same content
> + * objcg - the obj_cgroup(actually memcg) this entry belongs to


Again, not the place to document that objcg is an abstraction layer
above a memcg.

I would do something like:
objcg - the obj_cgroup that the compressed memory is charged to

>
>   * lru - handle to the pool's lru used to evict pages.
>   */
>  struct zswap_entry {
> --
> 2.34.1
>
>