The patch titled
Subject: lib: list_sort.c: Limit number of unused cmp callbacks
has been added to the -mm tree. Its filename is
lib-list_sortc-limit-number-of-unused-cmp-callbacks.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/lib-list_sortc-limit-number-of-unused-cmp-callbacks.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/lib-list_sortc-limit-number-of-unused-cmp-callbacks.patch
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------------------------------------------------------
From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Subject: lib: list_sort.c: Limit number of unused cmp callbacks
The helper merge_and_restore_back_links() makes sure to call the caller's
cmp function during the final ->prev pointer fixup, so that the cmp
function may call cond_resched(). However, if the cmp function does not
call cond_resched() at all, this is entirely redundant. If it does, doing
at least two function calls for every two pointer assignments is a bit
excessive. This patch limits the calls to once for every 256 iterations.
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
Cc: Don Mullis <don.mullis@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/list_sort.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff -puN lib/list_sort.c~lib-list_sortc-limit-number-of-unused-cmp-callbacks lib/list_sort.c
--- a/lib/list_sort.c~lib-list_sortc-limit-number-of-unused-cmp-callbacks
+++ a/lib/list_sort.c
@@ -47,6 +47,7 @@ static void merge_and_restore_back_links
struct list_head *a, struct list_head *b)
{
struct list_head *tail = head;
+ u8 count = 0;
while (a && b) {
/* if equal, take 'a' -- important for sort stability */
@@ -70,7 +71,8 @@ static void merge_and_restore_back_links
* element comparison is needed, so the client's cmp()
* routine can invoke cond_resched() periodically.
*/
- (*cmp)(priv, tail->next, tail->next);
+ if (unlikely(!(++count)))
+ (*cmp)(priv, tail->next, tail->next);
tail->next->prev = tail;
tail = tail->next;
_
Patches currently in -mm which might be from linux@xxxxxxxxxxxxxxxxxx are
origin.patch
lib-list_sort_test-return-enomem-when-allocation-fails.patch
lib-list_sort_test-add-extra-corruption-check.patch
lib-list_sort_test-simplify-and-harden-cleanup.patch
lib-list_sortc-limit-number-of-unused-cmp-callbacks.patch
checkpatchpl-also-suggest-else-if-when-if-follows-brace.patch
linux-next.patch
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