svn commit: r364786 - head/sys/vm

[Conrad Meyer]

Author: cem
Date: Tue Aug 25 21:36:56 2020
New Revision: 364786
URL: https://svnweb.freebsd.org/changeset/base/364786

Log:
  vm_pageout: Scale worker threads with CPUs
  
  Autoscale vm_pageout worker threads from r364129 with CPU count.  The
  default is arbitrarily chosen to be 16 CPUs per worker thread, but can
  be adjusted with the vm.pageout_cpus_per_thread tunable.
  
  There will never be less than 1 thread per populated NUMA domain, and
  the previous arbitrary upper limit (at most ncpus/2 threads per NUMA
  domain) is preserved.
  
  Care is taken to gracefully handle asymmetric NUMA nodes, such as empty
  node systems (e.g., AMD 2990WX) and systems with nodes of varying size
  (e.g., some larger >20 core Intel Haswell/Broadwell Xeon).
  
  Reviewed by:	kib, markj
  Sponsored by:	Isilon
  Differential Revision:	https://reviews.freebsd.org/D26152

Modified:
  head/sys/vm/vm_pageout.c

Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c	Tue Aug 25 21:07:27 2020	(r364785)
+++ head/sys/vm/vm_pageout.c	Tue Aug 25 21:36:56 2020	(r364786)
@@ -165,11 +165,10 @@ SYSCTL_INT(_vm, OID_AUTO, pageout_update_period,
 	CTLFLAG_RWTUN, &vm_pageout_update_period, 0,
 	"Maximum active LRU update period");
 
-/* Access with get_pageout_threads_per_domain(). */
-static int pageout_threads_per_domain = 1;
-SYSCTL_INT(_vm, OID_AUTO, pageout_threads_per_domain, CTLFLAG_RDTUN,
-    &pageout_threads_per_domain, 0,
-    "Number of worker threads comprising each per-domain pagedaemon");
+static int pageout_cpus_per_thread = 16;
+SYSCTL_INT(_vm, OID_AUTO, pageout_cpus_per_thread, CTLFLAG_RDTUN,
+    &pageout_cpus_per_thread, 0,
+    "Number of CPUs per pagedaemon worker thread");
   
 SYSCTL_INT(_vm, OID_AUTO, lowmem_period, CTLFLAG_RWTUN, &lowmem_period, 0,
 	"Low memory callback period");
@@ -2200,38 +2199,38 @@ vm_pageout_helper(void *arg)
 }
 
 static int
-get_pageout_threads_per_domain(void)
+get_pageout_threads_per_domain(const struct vm_domain *vmd)
 {
-	static bool resolved = false;
-	int half_cpus_per_dom;
+	unsigned total_pageout_threads, eligible_cpus, domain_cpus;
 
-	/*
-	 * This is serialized externally by the sorted autoconfig portion of
-	 * boot.
-	 */
-	if (__predict_true(resolved))
-		return (pageout_threads_per_domain);
+	if (VM_DOMAIN_EMPTY(vmd->vmd_domain))
+		return (0);
 
 	/*
 	 * Semi-arbitrarily constrain pagedaemon threads to less than half the
-	 * total number of threads in the system as an insane upper limit.
+	 * total number of CPUs in the system as an upper limit.
 	 */
-	half_cpus_per_dom = howmany(mp_ncpus / vm_ndomains, 2);
+	if (pageout_cpus_per_thread < 2)
+		pageout_cpus_per_thread = 2;
+	else if (pageout_cpus_per_thread > mp_ncpus)
+		pageout_cpus_per_thread = mp_ncpus;
 
-	if (pageout_threads_per_domain < 1) {
-		printf("Invalid tuneable vm.pageout_threads_per_domain value: "
-		    "%d out of valid range: [1-%d]; clamping to 1\n",
-		    pageout_threads_per_domain, half_cpus_per_dom);
-		pageout_threads_per_domain = 1;
-	} else if (pageout_threads_per_domain > half_cpus_per_dom) {
-		printf("Invalid tuneable vm.pageout_threads_per_domain value: "
-		    "%d out of valid range: [1-%d]; clamping to %d\n",
-		    pageout_threads_per_domain, half_cpus_per_dom,
-		    half_cpus_per_dom);
-		pageout_threads_per_domain = half_cpus_per_dom;
-	}
-	resolved = true;
-	return (pageout_threads_per_domain);
+	total_pageout_threads = howmany(mp_ncpus, pageout_cpus_per_thread);
+	domain_cpus = CPU_COUNT(&cpuset_domain[vmd->vmd_domain]);
+
+	/* Pagedaemons are not run in empty domains. */
+	eligible_cpus = mp_ncpus;
+	for (unsigned i = 0; i < vm_ndomains; i++)
+		if (VM_DOMAIN_EMPTY(i))
+			eligible_cpus -= CPU_COUNT(&cpuset_domain[i]);
+
+	/*
+	 * Assign a portion of the total pageout threads to this domain
+	 * corresponding to the fraction of pagedaemon-eligible CPUs in the
+	 * domain.  In asymmetric NUMA systems, domains with more CPUs may be
+	 * allocated more threads than domains with fewer CPUs.
+	 */
+	return (howmany(total_pageout_threads * domain_cpus, eligible_cpus));
 }
 
 /*
@@ -2288,7 +2287,7 @@ vm_pageout_init_domain(int domain)
 	    "pidctrl", CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, "");
 	pidctrl_init_sysctl(&vmd->vmd_pid, SYSCTL_CHILDREN(oid));
 
-	vmd->vmd_inactive_threads = get_pageout_threads_per_domain();
+	vmd->vmd_inactive_threads = get_pageout_threads_per_domain(vmd);
 }
 
 static void
@@ -2343,7 +2342,6 @@ vm_pageout(void)
 
 	p = curproc;
 	td = curthread;
-	pageout_threads = get_pageout_threads_per_domain();
 
 	mtx_init(&vm_oom_ratelim_mtx, "vmoomr", NULL, MTX_DEF);
 	swap_pager_swap_init();
@@ -2363,6 +2361,7 @@ vm_pageout(void)
 				panic("starting pageout for domain %d: %d\n",
 				    i, error);
 		}
+		pageout_threads = VM_DOMAIN(i)->vmd_inactive_threads;
 		for (j = 0; j < pageout_threads - 1; j++) {
 			error = kthread_add(vm_pageout_helper,
 			    (void *)(uintptr_t)i, p, NULL, 0, 0,