Fri May 15 22:27:04 2020 UTC ()

PR kern/55268: tmpfs is slow

uao_get(): in the PGO_LOCKED case, we're okay to allocate a new page as long
as the caller holds a write lock.  PGO_NOBUSY doesn't put a stop to that.


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diff -r1.139 -r1.140 src/sys/uvm/uvm_aobj.c

--- src/sys/uvm/uvm_aobj.c 2020/03/22 18:32:42	1.139
+++ src/sys/uvm/uvm_aobj.c 2020/05/15 22:27:04	1.140

 @@ -1,14 +1,14 @@
-/*	$NetBSD: uvm_aobj.c,v 1.139 2020/03/22 18:32:42 ad Exp $	*/
+/*	$NetBSD: uvm_aobj.c,v 1.140 2020/05/15 22:27:04 ad Exp $	*/
 /*
  * Copyright (c) 1998 Chuck Silvers, Charles D. Cranor and
  *                    Washington University.
  * All rights reserved.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
 @@ -28,27 +28,27 @@
  * from: Id: uvm_aobj.c,v 1.1.2.5 1998/02/06 05:14:38 chs Exp
  */
 /*
  * uvm_aobj.c: anonymous memory uvm_object pager
+ *
  * author: Chuck Silvers <chuq@chuq.com>
  * started: Jan-1998
+ *
  * - design mostly from Chuck Cranor
  */
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_aobj.c,v 1.139 2020/03/22 18:32:42 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_aobj.c,v 1.140 2020/05/15 22:27:04 ad Exp $");
 #ifdef _KERNEL_OPT
 #include "opt_uvmhist.h"
 #endif
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/kernel.h>
 #include <sys/kmem.h>
 #include <sys/pool.h>
 #include <sys/atomic.h>
 #include <uvm/uvm.h>
 @@ -817,58 +817,61 @@ uao_get(struct uvm_object *uobj, voff_t
 	   (access_type & VM_PROT_WRITE) == 0));
 	/*
  	 * get number of pages
  	 */
 	maxpages = *npagesp;
 	/*
  	 * step 1: handled the case where fault data structures are locked.
  	 */
 	if (flags & PGO_LOCKED) {
 		krw_t lktype = rw_lock_op(uobj->vmobjlock);
 		/*
  		 * step 1a: get pages that are already resident.   only do
 		 * this if the data structures are locked (i.e. the first
 		 * time through).
  		 */
 		done = true;	/* be optimistic */
 		gotpages = 0;	/* # of pages we got so far */
 		for (lcv = 0, current_offset = offset ; lcv < maxpages ;
 		    lcv++, current_offset += PAGE_SIZE) {
 			/* do we care about this page?  if not, skip it */
 			if (pps[lcv] == PGO_DONTCARE)
 				continue;
 			ptmp = uvm_pagelookup(uobj, current_offset);
 			/*
  			 * if page is new, attempt to allocate the page,
-			 * zero-fill'd.  we can only do this if busying
+			 * zero-fill'd.  we can only do this if the caller
-			 * pages, as otherwise the object is read locked.
+			 * holds a write lock.
  			 */
-			if ((flags & PGO_NOBUSY) == 0 && ptmp == NULL &&
+			if (ptmp == NULL && lktype == RW_WRITER &&
 			    uao_find_swslot(uobj,
 			    current_offset >> PAGE_SHIFT) == 0) {
 				ptmp = uao_pagealloc(uobj, current_offset,
 				    UVM_FLAG_COLORMATCH|UVM_PGA_ZERO);
 				if (ptmp) {
 					/* new page */
 					ptmp->flags &= ~(PG_FAKE);
 					uvm_pagemarkdirty(ptmp,
 					    UVM_PAGE_STATUS_UNKNOWN);
 					if ((flags & PGO_NOBUSY) != 0)
 						ptmp->flags &= ~PG_BUSY;
 					goto gotpage;
+				}
+			}
 			/*
 			 * to be useful must get a non-busy page
 			 */
 			if (ptmp == NULL || (ptmp->flags & PG_BUSY) != 0) {
 				if (lcv == centeridx ||
 				    (flags & PGO_ALLPAGES) != 0)
 					/* need to do a wait or I/O! */
 					done = false;