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Fix UMA's first-touch policy on systems with empty domains.

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Suppose a thread is running on a CPU in a NUMA domain with no physical
RAM.  When an item is freed to a first-touch zone, it ends up in the
cross-domain bucket.  When the bucket is full, it gets placed in another
domain's bucket queue.  However, when allocating an item, UMA will
always go to the keg upon a per-CPU cache miss because the empty
domain's bucket queue will always be empty.  This means that a non-empty
domain's bucket queues can grow very rapidly on such systems.  For
example, it can easily cause mbuf allocation failures when the zone
limit is reached.

Change cache_alloc() to follow a round-robin policy when running on an
empty domain.

Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D25355
This commit is contained in:
Mark Johnston 2020-06-28 21:35:04 +00:00
parent 3507b8d467
commit 8c277118d8
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=362740
1 changed files with 6 additions and 4 deletions
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10
sys/vm/uma_core.c
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@ -3398,7 +3398,7 @@ static __noinline bool
cache_alloc(uma_zone_t zone, uma_cache_t cache, void *udata, int flags)
{
uma_bucket_t bucket;
int domain;
int curdomain, domain;
bool new;
CRITICAL_ASSERT(curthread);
@ -3445,7 +3445,8 @@ cache_alloc(uma_zone_t zone, uma_cache_t cache, void *udata, int flags)
* the critical section.
*/
domain = PCPU_GET(domain);
if ((cache_uz_flags(cache) & UMA_ZONE_ROUNDROBIN) != 0)
if ((cache_uz_flags(cache) & UMA_ZONE_ROUNDROBIN) != 0 ||
VM_DOMAIN_EMPTY(domain))
domain = zone_domain_highest(zone, domain);
bucket = cache_fetch_bucket(zone, cache, domain);
if (bucket == NULL) {
@ -3470,7 +3471,8 @@ cache_alloc(uma_zone_t zone, uma_cache_t cache, void *udata, int flags)
cache = &zone->uz_cpu[curcpu];
if (cache->uc_allocbucket.ucb_bucket == NULL &&
((cache_uz_flags(cache) & UMA_ZONE_FIRSTTOUCH) == 0 ||
domain == PCPU_GET(domain))) {
(curdomain = PCPU_GET(domain)) == domain ||
VM_DOMAIN_EMPTY(curdomain))) {
if (new)
atomic_add_long(&ZDOM_GET(zone, domain)->uzd_imax,
bucket->ub_cnt);
@ -3877,7 +3879,7 @@ zone_alloc_bucket(uma_zone_t zone, void *udata, int domain, int flags)
/* Avoid allocs targeting empty domains. */
if (domain != UMA_ANYDOMAIN && VM_DOMAIN_EMPTY(domain))
domain = UMA_ANYDOMAIN;
if ((zone->uz_flags & UMA_ZONE_ROUNDROBIN) != 0)
else if ((zone->uz_flags & UMA_ZONE_ROUNDROBIN) != 0)
domain = UMA_ANYDOMAIN;
if (zone->uz_max_items > 0)