Eric W. Biederman [ebiederm@xxxxxxxxxxxx] wrote:
| > I will post a version of the patch outside this patchset with min
| > and max parameters and we can see if it can be optimized/beautified.
|
| Thanks,
| Eric
Here is the patch. alloc_pid() calls alloc_pidmap() as follows:
- nr = alloc_pidmap(tmp);
+ min = max = 0;
+ if (target_pids) {
+ min = target_pids[i];
+ max = min + 1;
+ }
+ nr = alloc_pidmap(tmp, min, max);
It does look like this patch executes a bit more code even in the common
case but let me know if you think this is better.
---
From: Sukadev Bhattiprolu <suka@suka.(none)>
Date: Tue, 20 Oct 2009 17:01:18 -0700
Subject: [PATCH] Add min and max parameters to alloc_pidmap()
With support for setting a specific pid number for a process, alloc_pidmap()
will need a 'min' and a 'max' parameter.
---
kernel/pid.c | 47 ++++++++++++++++++++++++++++++++++-------------
1 files changed, 34 insertions(+), 13 deletions(-)
diff --git a/kernel/pid.c b/kernel/pid.c
index c4d9914..56e13c1 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -147,18 +147,30 @@ static int alloc_pidmap_page(struct pidmap *map)
return 0;
}
-static int alloc_pidmap(struct pid_namespace *pid_ns)
+static int alloc_pidmap(struct pid_namespace *pid_ns, int min, int max)
{
int i, offset, max_scan, pid, last = pid_ns->last_pid;
int rc = -EAGAIN;
struct pidmap *map;
- pid = last + 1;
- if (pid >= pid_max)
- pid = RESERVED_PIDS;
+ if (min < 0 || max < 0 || max > pid_max)
+ return -EINVAL;
+
+ if (!max)
+ max = pid_max;
+
+ pid = min;
+ if (pid && pid >= max)
+ return -EINVAL;
+ else if (!pid) {
+ pid = last + 1;
+ if (pid >= pid_max)
+ pid = RESERVED_PIDS;
+ }
+
offset = pid & BITS_PER_PAGE_MASK;
map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
- max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
+ max_scan = (max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
for (i = 0; i <= max_scan; ++i) {
rc = alloc_pidmap_page(map);
if (rc)
@@ -168,7 +180,12 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
do {
if (!test_and_set_bit(offset, map->page)) {
atomic_dec(&map->nr_free);
- pid_ns->last_pid = pid;
+ /*
+ * 'last_pid' only makes sense when
+ * choosing from entire range
+ */
+ if (!min)
+ pid_ns->last_pid = pid;
return pid;
}
offset = find_next_offset(map, offset);
@@ -179,22 +196,26 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
* bitmap block and the final block was the same
* as the starting point, pid is before last_pid.
*/
- } while (offset < BITS_PER_PAGE && pid < pid_max &&
+ } while (offset < BITS_PER_PAGE && pid < max &&
(i != max_scan || pid < last ||
!((last+1) & BITS_PER_PAGE_MASK)));
}
- if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
+ if (map < &pid_ns->pidmap[(max-1)/BITS_PER_PAGE]) {
++map;
offset = 0;
} else {
map = &pid_ns->pidmap[0];
offset = RESERVED_PIDS;
- if (unlikely(last == offset)) {
- rc = -EAGAIN;
- break;
- }
}
pid = mk_pid(pid_ns, map, offset);
+ /*
+ * If we are back to where we started, well, no pids are
+ * currently available in selected range.
+ */
+ if (pid < min || unlikely(last == offset)) {
+ rc = -EAGAIN;
+ break;
+ }
}
return rc;
}
@@ -272,7 +293,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
tmp = ns;
for (i = ns->level; i >= 0; i--) {
- nr = alloc_pidmap(tmp);
+ nr = alloc_pidmap(tmp, 0, 0);
if (nr < 0)
goto out_free;
--
1.6.0.4
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