forked from Minki/linux
list: add function list_rotate_to_front()
Patch series "mm: Use slab_list list_head instead of lru", v5. Currently the slab allocators (ab)use the struct page 'lru' list_head. We have a list head for slab allocators to use, 'slab_list'. During v2 it was noted by Christoph that the SLOB allocator was reaching into a list_head, this version adds 2 patches to the front of the set to fix that. Clean up all three allocators by using the 'slab_list' list_head instead of overloading the 'lru' list_head. This patch (of 7): Currently if we wish to rotate a list until a specific item is at the front of the list we can call list_move_tail(head, list). Note that the arguments are the reverse way to the usual use of list_move_tail(list, head). This is a hack, it depends on the developer knowing how the list_head operates internally which violates the layer of abstraction offered by the list_head. Also, it is not intuitive so the next developer to come along must study list.h in order to fully understand what is meant by the call, while this is 'good for' the developer it makes reading the code harder. We should have an function appropriately named that does this if there are users for it intree. By grep'ing the tree for list_move_tail() and list_tail() and attempting to guess the argument order from the names it seems there is only one place currently in the tree that does this - the slob allocatator. Add function list_rotate_to_front() to rotate a list until the specified item is at the front of the list. Link: http://lkml.kernel.org/r/20190402230545.2929-2-tobin@kernel.org Signed-off-by: Tobin C. Harding <tobin@kernel.org> Reviewed-by: Christoph Lameter <cl@linux.com> Reviewed-by: Roman Gushchin <guro@fb.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -270,6 +270,24 @@ static inline void list_rotate_left(struct list_head *head)
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}
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}
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/**
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* list_rotate_to_front() - Rotate list to specific item.
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* @list: The desired new front of the list.
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* @head: The head of the list.
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*
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* Rotates list so that @list becomes the new front of the list.
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*/
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static inline void list_rotate_to_front(struct list_head *list,
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struct list_head *head)
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{
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/*
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* Deletes the list head from the list denoted by @head and
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* places it as the tail of @list, this effectively rotates the
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* list so that @list is at the front.
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*/
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list_move_tail(head, list);
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}
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/**
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* list_is_singular - tests whether a list has just one entry.
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* @head: the list to test.
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