Avoid resource deadlocks when one domain has exhausted its memory. Attempt

other allowed domains if the requested domain is below the minimum paging
threshold.  Block in fork only if all domains available to the forking
thread are below the severe threshold rather than any.

Submitted by:	jeff
Reported by:	mjg
Reviewed by:	alc, kib, markj
Approved by:	re (rgrimes)
Differential Revision:	https://reviews.freebsd.org/D16191

sys/sys/vmmeter.h

@@ -187,6 +187,13 @@ vm_page_count_severe(void)
 	return (!DOMAINSET_EMPTY(&vm_severe_domains));
 }
 
+static inline int
+vm_page_count_severe_set(domainset_t *mask)
+{
+
+	return (DOMAINSET_SUBSET(&vm_severe_domains, mask));
+}
+
 /*
  * Return TRUE if we are under our minimum low-free-pages threshold.
  *

sys/vm/vm_domainset.c

@@ -100,6 +100,8 @@ vm_domainset_iter_init(struct vm_domainset_iter *di, struct vm_object *obj,
 			pindex += (((uintptr_t)obj) / sizeof(*obj));
 		di->di_offset = pindex;
 	}
+	/* Skip zones below min on the first pass. */
+	di->di_minskip = true;
 }
 
 static void
@@ -213,6 +215,8 @@ vm_domainset_iter_page_init(struct vm_domainset_iter *di, struct vm_object *obj,
 	*req = (di->di_flags & ~(VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL)) |
 	    VM_ALLOC_NOWAIT;
 	vm_domainset_iter_first(di, domain);
+	if (DOMAINSET_ISSET(*domain, &vm_min_domains))
+		vm_domainset_iter_page(di, domain, req);
 }
 
 int
@@ -227,8 +231,15 @@ vm_domainset_iter_page(struct vm_domainset_iter *di, int *domain, int *req)
 		return (ENOMEM);
 
 	/* If there are more domains to visit we run the iterator. */
-	if (--di->di_n != 0) {
+	while (--di->di_n != 0) {
 		vm_domainset_iter_next(di, domain);
+		if (!di->di_minskip ||
+		    !DOMAINSET_ISSET(*domain, &vm_min_domains))
+			return (0);
+	}
+	if (di->di_minskip) {
+		di->di_minskip = false;
+		vm_domainset_iter_first(di, domain);
 		return (0);
 	}
 
@@ -258,6 +269,8 @@ vm_domainset_iter_malloc_init(struct vm_domainset_iter *di,
 	di->di_flags = *flags;
 	*flags = (di->di_flags & ~M_WAITOK) | M_NOWAIT;
 	vm_domainset_iter_first(di, domain);
+	if (DOMAINSET_ISSET(*domain, &vm_min_domains))
+		vm_domainset_iter_malloc(di, domain, flags);
 }
 
 int
@@ -265,8 +278,17 @@ vm_domainset_iter_malloc(struct vm_domainset_iter *di, int *domain, int *flags)
 {
 
 	/* If there are more domains to visit we run the iterator. */
-	if (--di->di_n != 0) {
+	while (--di->di_n != 0) {
 		vm_domainset_iter_next(di, domain);
+		if (!di->di_minskip ||
+		    !DOMAINSET_ISSET(*domain, &vm_min_domains))
+			return (0);
+	}
+
+	/* If we skipped zones below min start the search from the beginning. */
+	if (di->di_minskip) {
+		di->di_minskip = false;
+		vm_domainset_iter_first(di, domain);
 		return (0);
 	}
 

sys/vm/vm_domainset.h

@@ -34,9 +34,10 @@ struct vm_domainset_iter {
 	struct domainset	*di_domain;
 	int			*di_iter;
 	vm_pindex_t		di_offset;
-	int			di_policy;
 	int			di_flags;
-	int			di_n;
+	uint16_t		di_policy;
+	domainid_t		di_n;
+	bool			di_minskip;
 };
 
 int	vm_domainset_iter_page(struct vm_domainset_iter *, int *, int *);
@@ -46,4 +47,6 @@ int	vm_domainset_iter_malloc(struct vm_domainset_iter *, int *, int *);
 void	vm_domainset_iter_malloc_init(struct vm_domainset_iter *,
 	    struct vm_object *, int *, int *);
 
+void	vm_wait_doms(const domainset_t *);
+
 #endif  /* __VM_DOMAINSET_H__ */

sys/vm/vm_fault.c

@@ -548,6 +548,7 @@ vm_fault_hold(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 {
 	struct faultstate fs;
 	struct vnode *vp;
+	struct domainset *dset;
 	vm_object_t next_object, retry_object;
 	vm_offset_t e_end, e_start;
 	vm_pindex_t retry_pindex;
@@ -791,7 +792,11 @@ RetryFault:;
 			 * there, and allocation can fail, causing
 			 * restart and new reading of the p_flag.
 			 */
-			if (!vm_page_count_severe() || P_KILLED(curproc)) {
+			dset = fs.object->domain.dr_policy;
+			if (dset == NULL)
+				dset = curthread->td_domain.dr_policy;
+			if (!vm_page_count_severe_set(&dset->ds_mask) ||
+			    P_KILLED(curproc)) {
 #if VM_NRESERVLEVEL > 0
 				vm_object_color(fs.object, atop(vaddr) -
 				    fs.pindex);
@@ -806,7 +811,7 @@ RetryFault:;
 			}
 			if (fs.m == NULL) {
 				unlock_and_deallocate(&fs);
-				vm_waitpfault();
+				vm_waitpfault(dset);
 				goto RetryFault;
 			}
 		}

sys/vm/vm_glue.c

@@ -92,6 +92,7 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm.h>
 #include <vm/vm_param.h>
 #include <vm/pmap.h>
+#include <vm/vm_domainset.h>
 #include <vm/vm_map.h>
 #include <vm/vm_page.h>
 #include <vm/vm_pageout.h>
@@ -534,6 +535,7 @@ vm_forkproc(struct thread *td, struct proc *p2, struct thread *td2,
     struct vmspace *vm2, int flags)
 {
 	struct proc *p1 = td->td_proc;
+	struct domainset *dset;
 	int error;
 
 	if ((flags & RFPROC) == 0) {
@@ -557,9 +559,9 @@ vm_forkproc(struct thread *td, struct proc *p2, struct thread *td2,
 		p2->p_vmspace = p1->p_vmspace;
 		atomic_add_int(&p1->p_vmspace->vm_refcnt, 1);
 	}
-
-	while (vm_page_count_severe()) {
-		vm_wait_severe();
+	dset = td2->td_domain.dr_policy;
+	while (vm_page_count_severe_set(&dset->ds_mask)) {
+		vm_wait_doms(&dset->ds_mask);
 	}
 
 	if ((flags & RFMEM) == 0) {

sys/vm/vm_page.c

@@ -2935,7 +2935,7 @@ vm_wait_count(void)
 	return (vm_severe_waiters + vm_min_waiters + vm_pageproc_waiters);
 }
 
-static void
+void
 vm_wait_doms(const domainset_t *wdoms)
 {
 
@@ -2961,9 +2961,9 @@ vm_wait_doms(const domainset_t *wdoms)
 		mtx_lock(&vm_domainset_lock);
 		if (DOMAINSET_SUBSET(&vm_min_domains, wdoms)) {
 			vm_min_waiters++;
-			msleep(&vm_min_domains, &vm_domainset_lock, PVM,
-			    "vmwait", 0);
-		}
+			msleep(&vm_min_domains, &vm_domainset_lock,
+			    PVM | PDROP, "vmwait", 0);
+		} else
 			mtx_unlock(&vm_domainset_lock);
 	}
 }
@@ -3069,14 +3069,20 @@ vm_domain_alloc_fail(struct vm_domain *vmd, vm_object_t object, int req)
  *	  this balance without careful testing first.
  */
 void
-vm_waitpfault(void)
+vm_waitpfault(struct domainset *dset)
 {
 
+	/*
+	 * XXX Ideally we would wait only until the allocation could
+	 * be satisfied.  This condition can cause new allocators to
+	 * consume all freed pages while old allocators wait.
+	 */
 	mtx_lock(&vm_domainset_lock);
-	if (vm_page_count_min()) {
+	if (DOMAINSET_SUBSET(&vm_min_domains, &dset->ds_mask)) {
 		vm_min_waiters++;
-		msleep(&vm_min_domains, &vm_domainset_lock, PUSER, "pfault", 0);
-	}
+		msleep(&vm_min_domains, &vm_domainset_lock, PUSER | PDROP,
+		    "pfault", 0);
+	} else
 		mtx_unlock(&vm_domainset_lock);
 }
 

sys/vm/vm_pageout.h

@@ -96,7 +96,7 @@ extern int vm_pageout_page_count;
  */
 
 void vm_wait(vm_object_t obj);
-void vm_waitpfault(void);
+void vm_waitpfault(struct domainset *);
 void vm_wait_domain(int domain);
 void vm_wait_min(void);
 void vm_wait_severe(void);