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authorEric Dumazet <dada1@cosmosbay.com>2008-02-06 01:37:56 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-06 10:41:09 -0800
commit1bf47346d75790ebd2563d909d48046961c7ffd5 (patch)
tree0f478764beb8dc4e0c71c5f3d6a657535579fe3a /include/linux
parent6b2fb3c65844452bb9e8b449d50863d1b36c5dc0 (diff)
kernel/sys.c: get rid of expensive divides in groups_sort()
groups_sort() can be quite long if user loads a large gid table. This is because GROUP_AT(group_info, some_integer) uses an integer divide. So having to do XXX thousand divides during one syscall can lead to very high latencies. (NGROUPS_MAX=65536) In the past (25 Mar 2006), an analog problem was found in groups_search() (commit d74beb9f33a5f16d2965f11b275e401f225c949d ) and at that time I changed some variables to unsigned int. I believe that a more generic fix is to make sure NGROUPS_PER_BLOCK is unsigned. Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/sched.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9c13be3a21e8..7c8ca05c3cae 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -810,7 +810,7 @@ static inline int above_background_load(void)
struct io_context; /* See blkdev.h */
#define NGROUPS_SMALL 32
-#define NGROUPS_PER_BLOCK ((int)(PAGE_SIZE / sizeof(gid_t)))
+#define NGROUPS_PER_BLOCK ((unsigned int)(PAGE_SIZE / sizeof(gid_t)))
struct group_info {
int ngroups;
atomic_t usage;