mm: zswap: update comment for struct zswap_entry

Since commit 0bb48849 ("mm: zswap: remove zswap_header"), the 'offset'
has been replaced by swpentry, update the comment for it, and also add
comment for 'objcg'.

Link: https://lkml.kernel.org/r/20230808062056.292950-1-xiujianfeng@huaweicloud.comSigned-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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 - 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 that the compressed memory is charged to
  * lru - handle to the pool's lru used to evict pages.
  */
 struct zswap_entry {