Date: Mon, 10 Aug 2020 20:34:46 +0000 (UTC) From: Mark Johnston <markj@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r364090 - head/sys/vm Message-ID: <202008102034.07AKYk6G068581@repo.freebsd.org>
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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);help
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