The patch titled
Subject: mm/slob.c: respect list_head abstraction layer
has been added to the -mm tree. Its filename is
slob-respect-list_head-abstraction-layer.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/slob-respect-list_head-abstraction-layer.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/slob-respect-list_head-abstraction-layer.patch
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------------------------------------------------------
From: "Tobin C. Harding" <tobin@xxxxxxxxxx>
Subject: mm/slob.c: respect list_head abstraction layer
Currently we reach inside the list_head. This is a violation of the layer
of abstraction provided by the list_head. It makes the code fragile.
More importantly it makes the code wicked hard to understand.
The code logic is based on the page in which an allocation was made, we
want to modify the slob_list we are working on to have this page at the
front. We already have a function to check if an entry is at the front of
the list. Recently a function was added to list.h to do the list
rotation. We can use these two functions to reduce line count, reduce
code fragility, and reduce cognitive load required to read the code.
Use list_head functions to interact with lists thereby maintaining the
abstraction provided by the list_head structure.
Link: http://lkml.kernel.org/r/20190318000234.22049-3-tobin@xxxxxxxxxx
Signed-off-by: Tobin C. Harding <tobin@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slob.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
--- a/mm/slob.c~slob-respect-list_head-abstraction-layer
+++ a/mm/slob.c
@@ -268,8 +268,7 @@ static void *slob_page_alloc(struct page
*/
static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
{
- struct page *sp;
- struct list_head *prev;
+ struct page *sp, *prev, *next;
struct list_head *slob_list;
slob_t *b = NULL;
unsigned long flags;
@@ -296,18 +295,27 @@ static void *slob_alloc(size_t size, gfp
if (sp->units < SLOB_UNITS(size))
continue;
+ /*
+ * Cache previous entry because slob_page_alloc() may
+ * remove sp from slob_list.
+ */
+ prev = list_prev_entry(sp, lru);
+
/* Attempt to alloc */
- prev = sp->lru.prev;
b = slob_page_alloc(sp, size, align);
if (!b)
continue;
- /* Improve fragment distribution and reduce our average
+ next = list_next_entry(prev, lru); /* This may or may not be sp */
+
+ /*
+ * Improve fragment distribution and reduce our average
* search time by starting our next search here. (see
- * Knuth vol 1, sec 2.5, pg 449) */
- if (prev != slob_list->prev &&
- slob_list->next != prev->next)
- list_move_tail(slob_list, prev->next);
+ * Knuth vol 1, sec 2.5, pg 449)
+ */
+ if (!list_is_first(&next->lru, slob_list))
+ list_rotate_to_front(&next->lru, slob_list);
+
break;
}
spin_unlock_irqrestore(&slob_lock, flags);
_
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
