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Don't allocate new unnecessary pages when devstat_alloc() looses the

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run for re-acuiring the lock, but recheck if new pages are allocatable
from the pool and free the previously allocated ones.

Tested by:	pho, Giovanni Trematerra
		<giovanni dot trematerra at gmail dot com>
This commit is contained in:
Attilio Rao 2009-09-18 13:48:38 +00:00
parent 6949482f89
commit 39df6da8cc
1 changed files with 27 additions and 16 deletions
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43
sys/kern/subr_devstat.c
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@ -469,7 +469,7 @@ static struct devstat *
devstat_alloc(void)
{
struct devstat *dsp;
struct statspage *spp;
struct statspage *spp, *spp2;
u_int u;
static int once;
@ -479,6 +479,7 @@ devstat_alloc(void)
UID_ROOT, GID_WHEEL, 0400, DEVSTAT_DEVICE_NAME);
once = 1;
}
spp2 = NULL;
mtx_lock(&devstat_mutex);
for (;;) {
TAILQ_FOREACH(spp, &pagelist, list) {
@ -487,24 +488,30 @@ devstat_alloc(void)
}
if (spp != NULL)
break;
/*
* We had no free slot in any of our pages, drop the mutex
* and get another page. In theory we could have more than
* one process doing this at the same time and consequently
* we may allocate more pages than we will need. That is
* Just Too Bad[tm], we can live with that.
*/
mtx_unlock(&devstat_mutex);
spp = malloc(sizeof *spp, M_DEVSTAT, M_ZERO | M_WAITOK);
spp->stat = malloc(PAGE_SIZE, M_DEVSTAT, M_ZERO | M_WAITOK);
spp->nfree = statsperpage;
mtx_lock(&devstat_mutex);
spp2 = malloc(sizeof *spp, M_DEVSTAT, M_ZERO | M_WAITOK);
spp2->stat = malloc(PAGE_SIZE, M_DEVSTAT, M_ZERO | M_WAITOK);
spp2->nfree = statsperpage;
/*
* It would make more sense to add the new page at the head
* but the order on the list determine the sequence of the
* mapping so we can't do that.
* If free statspages were added while the lock was released
* just reuse them.
*/
TAILQ_INSERT_TAIL(&pagelist, spp, list);
mtx_lock(&devstat_mutex);
TAILQ_FOREACH(spp, &pagelist, list)
if (spp->nfree > 0)
break;
if (spp == NULL) {
spp = spp2;
/*
* It would make more sense to add the new page at the
* head but the order on the list determine the
* sequence of the mapping so we can't do that.
*/
TAILQ_INSERT_TAIL(&pagelist, spp, list);
} else
break;
}
dsp = spp->stat;
for (u = 0; u < statsperpage; u++) {
@ -515,6 +522,10 @@ devstat_alloc(void)
spp->nfree--;
dsp->allocated = 1;
mtx_unlock(&devstat_mutex);
if (spp2 != NULL && spp2 != spp) {
free(spp2->stat, M_DEVSTAT);
free(spp2, M_DEVSTAT);
}
return (dsp);
}