Add a function to pull a sub list containing up to @cnt nodes from @old list. This is beneficial to performance in scenarios where N free nodes are pulled from the global list to the local list, or N free nodes are pushed from the local list to the global list. Because the old sub list is no longer split and then spliced into the new list one by one, this also enhances readability.
Signed-off-by: Zhen Lei thunder.leizhen@huawei.com --- include/linux/list.h | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+)
diff --git a/include/linux/list.h b/include/linux/list.h index 5f4b0a39cf46a37..9fb58cbceb1245c 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -1210,4 +1210,48 @@ static inline size_t hlist_count_nodes(struct hlist_head *head) return count; }
+/** + * hlist_cut_number - cut a list into two + * @new: a new list to add all removed entries + * @old: a list with entries + * @cnt: maximum of nodes need to be cut + * @last: save the last node of the new list + * + * This helper moves the initial part of @old, maximum of @cnt nodes, from + * @old to @new. @new should be an empty list or a list you do not care about + * losing its data. + * + * Returns the number of nodes in the @new list, maybe zero. + * + */ +static inline int hlist_cut_number(struct hlist_head *new, + struct hlist_head *old, int cnt, struct hlist_node **last) +{ + int nr = 0; + struct hlist_node *tmp, *pos = NULL; + + if (cnt <= 0) + return 0; + + hlist_for_each(tmp, old) { + nr++; + pos = tmp; + if (nr >= cnt) + break; + } + + *last = pos; + new->first = old->first; + + if (pos) { + new->first->pprev = &new->first; + old->first = pos->next; + if (old->first) + old->first->pprev = &old->first; + pos->next = NULL; + } + + return nr; +} + #endif