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Date:      Thu, 1 Oct 2020 19:17:03 +0000 (UTC)
From:      Bryan Drewery <bdrewery@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r366340 - head/sys/kern
Message-ID:  <202010011917.091JH3jX031245@repo.freebsd.org>
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Author: bdrewery
Date: Thu Oct  1 19:17:03 2020
New Revision: 366340
URL: https://svnweb.freebsd.org/changeset/base/366340

Log:
  Use unlocked page lookup for inmem() to avoid object lock contention
  
  Reviewed By:	kib, markj
  Sponsored by:	Dell EMC Isilon
  Submitted by:	mlaier
  Differential Revision:	https://reviews.freebsd.org/D26597

Modified:
  head/sys/kern/vfs_bio.c

Modified: head/sys/kern/vfs_bio.c
==============================================================================
--- head/sys/kern/vfs_bio.c	Thu Oct  1 19:06:07 2020	(r366339)
+++ head/sys/kern/vfs_bio.c	Thu Oct  1 19:17:03 2020	(r366340)
@@ -154,7 +154,7 @@ caddr_t __read_mostly unmapped_buf;
 /* Used below and for softdep flushing threads in ufs/ffs/ffs_softdep.c */
 struct proc *bufdaemonproc;
 
-static int inmem(struct vnode *vp, daddr_t blkno);
+static bool inmem(struct vnode *vp, daddr_t blkno);
 static void vm_hold_free_pages(struct buf *bp, int newbsize);
 static void vm_hold_load_pages(struct buf *bp, vm_offset_t from,
 		vm_offset_t to);
@@ -3586,20 +3586,21 @@ incore(struct bufobj *bo, daddr_t blkno)
  * it also hunts around in the VM system for the data.
  */
 
-static int
+static bool
 inmem(struct vnode * vp, daddr_t blkno)
 {
 	vm_object_t obj;
 	vm_offset_t toff, tinc, size;
-	vm_page_t m;
+	vm_page_t m, n;
 	vm_ooffset_t off;
+	int valid;
 
 	ASSERT_VOP_LOCKED(vp, "inmem");
 
 	if (incore(&vp->v_bufobj, blkno))
-		return 1;
+		return (1);
 	if (vp->v_mount == NULL)
-		return 0;
+		return (0);
 	obj = vp->v_object;
 	if (obj == NULL)
 		return (0);
@@ -3609,24 +3610,30 @@ inmem(struct vnode * vp, daddr_t blkno)
 		size = vp->v_mount->mnt_stat.f_iosize;
 	off = (vm_ooffset_t)blkno * (vm_ooffset_t)vp->v_mount->mnt_stat.f_iosize;
 
-	VM_OBJECT_RLOCK(obj);
 	for (toff = 0; toff < vp->v_mount->mnt_stat.f_iosize; toff += tinc) {
-		m = vm_page_lookup(obj, OFF_TO_IDX(off + toff));
-		if (!m)
-			goto notinmem;
+		m = vm_page_lookup_unlocked(obj, OFF_TO_IDX(off + toff));
+recheck:
+		if (m == NULL)
+			return (0);
+		/*
+		 * Consider page validity only if page mapping didn't change
+		 * during the check.
+		 */
+		valid = vm_page_is_valid(m,
+		    (vm_offset_t)((toff + off) & PAGE_MASK), tinc);
+		n = vm_page_lookup_unlocked(obj, OFF_TO_IDX(off + toff));
+		if (m != n) {
+			m = n;
+			goto recheck;
+		}
+		if (!valid)
+			return (0);
+
 		tinc = size;
 		if (tinc > PAGE_SIZE - ((toff + off) & PAGE_MASK))
 			tinc = PAGE_SIZE - ((toff + off) & PAGE_MASK);
-		if (vm_page_is_valid(m,
-		    (vm_offset_t) ((toff + off) & PAGE_MASK), tinc) == 0)
-			goto notinmem;
 	}
-	VM_OBJECT_RUNLOCK(obj);
-	return 1;
-
-notinmem:
-	VM_OBJECT_RUNLOCK(obj);
-	return (0);
+	return (1);
 }
 
 /*

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