svn commit: r364090 - head/sys/vm
Mark Johnston
markj at FreeBSD.org
Mon Aug 10 20:34:46 UTC 2020
Author: markj
Date: Mon Aug 10 20:34:45 2020
New Revision: 364090
URL: https://svnweb.freebsd.org/changeset/base/364090
Log:
Check the UMA zone's full bucket cache before short-circuiting an alloc.
The global "bucketdisable" flag indicates that we are in a low memory
situation and should avoid allocating buckets. However, in the
allocation path we were checking it before the full bucket cache and
bailing even if the cache is non-empty. Defer the check so that we have
a shot at allocating from the cache.
This came up because M_NOWAIT allocations from the buf trie node zone
must always succeed. In one scenario, all of the preallocated trie
nodes were in the bucket list, and a new slab allocation could not
succeed due to a memory shortage. The short-circuiting caused an
allocation failure which triggered a panic.
Reported by: pho
Reviewed by: cem
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D25980
Modified:
head/sys/vm/uma_core.c
Modified: head/sys/vm/uma_core.c
==============================================================================
--- head/sys/vm/uma_core.c Mon Aug 10 20:24:48 2020 (r364089)
+++ head/sys/vm/uma_core.c Mon Aug 10 20:34:45 2020 (r364090)
@@ -3429,12 +3429,6 @@ cache_alloc(uma_zone_t zone, uma_cache_t cache, void *
bucket_free(zone, bucket, udata);
}
- /* Short-circuit for zones without buckets and low memory. */
- if (zone->uz_bucket_size == 0 || bucketdisable) {
- critical_enter();
- return (false);
- }
-
/*
* Attempt to retrieve the item from the per-CPU cache has failed, so
* we must go back to the zone. This requires the zdom lock, so we
@@ -3449,11 +3443,12 @@ cache_alloc(uma_zone_t zone, uma_cache_t cache, void *
VM_DOMAIN_EMPTY(domain))
domain = zone_domain_highest(zone, domain);
bucket = cache_fetch_bucket(zone, cache, domain);
- if (bucket == NULL) {
+ if (bucket == NULL && zone->uz_bucket_size != 0 && !bucketdisable) {
bucket = zone_alloc_bucket(zone, udata, domain, flags);
new = true;
- } else
+ } else {
new = false;
+ }
CTR3(KTR_UMA, "uma_zalloc: zone %s(%p) bucket zone returned %p",
zone->uz_name, zone, bucket);
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