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uma: Avoid depleting keg reserves when filling a bucket

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zone_import() fetches a free or partially free slab from the keg and
then uses its items to populate an array, typically filling a bucket.
If a single allocation causes the keg to drop below its minimum reserve,
the inner loop ends.  However, if the bucket is still not full and
M_USE_RESERVE is specified, the outer loop will continue to fetch items
from the keg.

If M_USE_RESERVE is specified and the number of free items is below the
reserved limit, we should return only a single item.  Otherwise, if the
bucket size is larger than the reserve, all of the reserved items may
end up in a single per-CPU bucket, invisible to other CPUs.

Reviewed by:	rlibby
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D26771
This commit is contained in:
Mark Johnston 2020-10-19 16:55:03 +00:00
parent 6351771b7c
commit 1b2dcc8c54
1 changed files with 13 additions and 5 deletions
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18
sys/vm/uma_core.c
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@ -3734,10 +3734,17 @@ zone_import(void *arg, void **bucket, int max, int domain, int flags)
stripe = howmany(max, vm_ndomains);
#endif
dom = &keg->uk_domain[slab->us_domain];
while (slab->us_freecount && i < max) {
do {
bucket[i++] = slab_alloc_item(keg, slab);
if (dom->ud_free_items <= keg->uk_reserve)
break;
if (dom->ud_free_items <= keg->uk_reserve) {
/*
* Avoid depleting the reserve after a
* successful item allocation, even if
* M_USE_RESERVE is specified.
*/
KEG_UNLOCK(keg, slab->us_domain);
goto out;
}
#ifdef NUMA
/*
* If the zone is striped we pick a new slab for every
@ -3751,13 +3758,14 @@ zone_import(void *arg, void **bucket, int max, int domain, int flags)
vm_ndomains > 1 && --stripe == 0)
break;
#endif
}
} while (slab->us_freecount != 0 && i < max);
KEG_UNLOCK(keg, slab->us_domain);
/* Don't block if we allocated any successfully. */
flags &= ~M_WAITOK;
flags |= M_NOWAIT;
}
out:
return i;
}