The patch titled
Subject: include/linux/list.h: add list_rotate_to_front()
has been added to the -mm tree. Its filename is
list-add-function-list_rotate_to_front.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/list-add-function-list_rotate_to_front.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/list-add-function-list_rotate_to_front.patch
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------------------------------------------------------
From: "Tobin C. Harding" <tobin@xxxxxxxxxx>
Subject: include/linux/list.h: add list_rotate_to_front()
Patch series "mm: Use slab_list list_head instead of lru", v4.
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.
Patch 1 - Adds a function to rotate a list to a specified entry.
Patch 2 - Removes the code that reaches into list_head and instead uses
the list_head API including the newly defined function.
Patches 3-7 are unchanged from v3
Patch 3 (v2: patch 4) - Changes the SLOB allocator to use slab_list
instead of lru.
Patch 4 (v2: patch 1) - Makes no code changes, adds comments to #endif
statements.
Patch 5 (v2: patch 2) - Use slab_list instead of lru for SLUB allocator.
Patch 6 (v2: patch 3) - Use slab_list instead of lru for SLAB allocator.
Patch 7 (v2: patch 5) - Removes the now stale comment in the page struct
definition.
During v2 development patches were checked to see if the object file
before and after was identical. Clearly this will no longer be possible
for mm/slob.o, however this work is still of use to validate the
change from lru -> slab_list.
Patch 1 was tested with a module (creates and populates a list then
calls list_rotate_to_front() and verifies new order):
https://github.com/tcharding/ktest/tree/master/list_head
Patch 2 was tested with another module that does some basic slab
allocation and freeing to a newly created slab cache:
https://github.com/tcharding/ktest/tree/master/slab
Tested on a kernel with this in the config:
CONFIG_SLOB=y
CONFIG_SLAB_MERGE_DEFAULT=y
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 grepping 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/20190318000234.22049-2-tobin@xxxxxxxxxx
Signed-off-by: Tobin C. Harding <tobin@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/list.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
--- a/include/linux/list.h~list-add-function-list_rotate_to_front
+++ a/include/linux/list.h
@@ -271,6 +271,24 @@ static inline void list_rotate_left(stru
}
/**
+ * list_rotate_to_front() - Rotate list to specific item.
+ * @list: The desired new front of the list.
+ * @head: The head of the list.
+ *
+ * Rotates list so that @list becomes the new front of the list.
+ */
+static inline void list_rotate_to_front(struct list_head *list,
+ struct list_head *head)
+{
+ /*
+ * Deletes the list head from the list denoted by @head and
+ * places it as the tail of @list, this effectively rotates the
+ * list so that @list is at the front.
+ */
+ list_move_tail(head, list);
+}
+
+/**
* list_is_singular - tests whether a list has just one entry.
* @head: the list to test.
*/
_
Patches currently in -mm which might be from tobin@xxxxxxxxxx are
list-add-function-list_rotate_to_front.patch
slob-respect-list_head-abstraction-layer.patch
slob-use-slab_list-instead-of-lru.patch
slub-add-comments-to-endif-pre-processor-macros.patch
slub-use-slab_list-instead-of-lru.patch
slab-use-slab_list-instead-of-lru.patch
mm-remove-stale-comment-from-page-struct.patch
