Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1bf47346d75790ebd2563d909d48046961c7ffd5
Commit: 1bf47346d75790ebd2563d909d48046961c7ffd5
Parent: 6b2fb3c65844452bb9e8b449d50863d1b36c5dc0
Author: Eric Dumazet <[EMAIL PROTECTED]>
AuthorDate: Wed Feb 6 01:37:56 2008 -0800
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Wed Feb 6 10:41:09 2008 -0800
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 <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
include/linux/sched.h | 2 +-
kernel/sys.c | 20 ++++++++++----------
2 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9c13be3..7c8ca05 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;
diff --git a/kernel/sys.c b/kernel/sys.c
index 2b8e2da..e3c08d4 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1145,16 +1145,16 @@ static int groups_to_user(gid_t __user *grouplist,
struct group_info *group_info)
{
int i;
- int count = group_info->ngroups;
+ unsigned int count = group_info->ngroups;
for (i = 0; i < group_info->nblocks; i++) {
- int cp_count = min(NGROUPS_PER_BLOCK, count);
- int off = i * NGROUPS_PER_BLOCK;
- int len = cp_count * sizeof(*grouplist);
+ unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);
+ unsigned int len = cp_count * sizeof(*grouplist);
- if (copy_to_user(grouplist+off, group_info->blocks[i], len))
+ if (copy_to_user(grouplist, group_info->blocks[i], len))
return -EFAULT;
+ grouplist += NGROUPS_PER_BLOCK;
count -= cp_count;
}
return 0;
@@ -1165,16 +1165,16 @@ static int groups_from_user(struct group_info
*group_info,
gid_t __user *grouplist)
{
int i;
- int count = group_info->ngroups;
+ unsigned int count = group_info->ngroups;
for (i = 0; i < group_info->nblocks; i++) {
- int cp_count = min(NGROUPS_PER_BLOCK, count);
- int off = i * NGROUPS_PER_BLOCK;
- int len = cp_count * sizeof(*grouplist);
+ unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);
+ unsigned int len = cp_count * sizeof(*grouplist);
- if (copy_from_user(group_info->blocks[i], grouplist+off, len))
+ if (copy_from_user(group_info->blocks[i], grouplist, len))
return -EFAULT;
+ grouplist += NGROUPS_PER_BLOCK;
count -= cp_count;
}
return 0;
-
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