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Date:      Mon, 11 Nov 2019 16:59:50 +0000 (UTC)
From:      Doug Moore <dougm@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r354618 - head/sys/vm
Message-ID:  <201911111659.xABGxoND075506@repo.freebsd.org>
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Author: dougm
Date: Mon Nov 11 16:59:49 2019
New Revision: 354618
URL: https://svnweb.freebsd.org/changeset/base/354618

Log:
  swap_pager_meta_free() frees allocated blocks in a way that
  exploits the sparsity of allocated blocks in a range, without
  issuing an "are you there?" query for every block in the range.
  swap_pager_copy() is not so smart.  Modify the implementation
  of swap_pager_meta_free() slightly so that swap_pager_copy()
  can use that smarter implementation too.
  
  Based on an observation of: Yoshihiro Ota (ota_j.email.ne.jp)
  Reviewed by: kib,alc
  Tested by: pho
  Differential Revision: https://reviews.freebsd.org/D22280

Modified:
  head/sys/vm/swap_pager.c

Modified: head/sys/vm/swap_pager.c
==============================================================================
--- head/sys/vm/swap_pager.c	Mon Nov 11 16:11:15 2019	(r354617)
+++ head/sys/vm/swap_pager.c	Mon Nov 11 16:59:49 2019	(r354618)
@@ -422,6 +422,8 @@ static daddr_t	swp_pager_getswapspace(int *npages, int
  */
 static daddr_t swp_pager_meta_build(vm_object_t, vm_pindex_t, daddr_t);
 static void swp_pager_meta_free(vm_object_t, vm_pindex_t, vm_pindex_t);
+static void swp_pager_meta_transfer(vm_object_t src, vm_object_t dst,
+    vm_pindex_t pindex, vm_pindex_t count);
 static void swp_pager_meta_free_all(vm_object_t);
 static daddr_t swp_pager_meta_ctl(vm_object_t, vm_pindex_t, int);
 
@@ -933,6 +935,33 @@ swap_pager_reserve(vm_object_t object, vm_pindex_t sta
 	return (0);
 }
 
+static bool
+swp_pager_xfer_source(vm_object_t srcobject, vm_object_t dstobject,
+    vm_pindex_t pindex, daddr_t addr)
+{
+	daddr_t dstaddr;
+
+	if (swp_pager_meta_ctl(dstobject, pindex, 0) != SWAPBLK_NONE) {
+		/* Caller should destroy the source block. */
+		return (false);
+	}
+
+	/*
+	 * Destination has no swapblk and is not resident, transfer source.
+	 * swp_pager_meta_build() can sleep.
+	 */
+	vm_object_pip_add(srcobject, 1);
+	VM_OBJECT_WUNLOCK(srcobject);
+	vm_object_pip_add(dstobject, 1);
+	dstaddr = swp_pager_meta_build(dstobject, pindex, addr);
+	KASSERT(dstaddr == SWAPBLK_NONE,
+	    ("Unexpected destination swapblk"));
+	vm_object_pip_wakeup(dstobject);
+	VM_OBJECT_WLOCK(srcobject);
+	vm_object_pip_wakeup(srcobject);
+	return (true);
+}
+
 /*
  * SWAP_PAGER_COPY() -  copy blocks from source pager to destination pager
  *			and destroy the source.
@@ -956,8 +985,6 @@ void
 swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
     vm_pindex_t offset, int destroysource)
 {
-	vm_pindex_t i;
-	daddr_t dstaddr, n_free, s_free, srcaddr;
 
 	VM_OBJECT_ASSERT_WLOCKED(srcobject);
 	VM_OBJECT_ASSERT_WLOCKED(dstobject);
@@ -984,39 +1011,8 @@ swap_pager_copy(vm_object_t srcobject, vm_object_t dst
 	/*
 	 * Transfer source to destination.
 	 */
-	swp_pager_init_freerange(&s_free, &n_free);
-	for (i = 0; i < dstobject->size; ++i) {
-		srcaddr = swp_pager_meta_ctl(srcobject, i + offset, SWM_POP);
-		if (srcaddr == SWAPBLK_NONE)
-			continue;
-		dstaddr = swp_pager_meta_ctl(dstobject, i, 0);
-		if (dstaddr != SWAPBLK_NONE) {
-			/*
-			 * Destination has valid swapblk or it is represented
-			 * by a resident page.  We destroy the source block.
-			 */
-			swp_pager_update_freerange(&s_free, &n_free, srcaddr);
-			continue;
-		}
+	swp_pager_meta_transfer(srcobject, dstobject, offset, dstobject->size);
 
-		/*
-		 * Destination has no swapblk and is not resident,
-		 * copy source.
-		 *
-		 * swp_pager_meta_build() can sleep.
-		 */
-		vm_object_pip_add(srcobject, 1);
-		VM_OBJECT_WUNLOCK(srcobject);
-		vm_object_pip_add(dstobject, 1);
-		dstaddr = swp_pager_meta_build(dstobject, i, srcaddr);
-		KASSERT(dstaddr == SWAPBLK_NONE,
-		    ("Unexpected destination swapblk"));
-		vm_object_pip_wakeup(dstobject);
-		VM_OBJECT_WLOCK(srcobject);
-		vm_object_pip_wakeup(srcobject);
-	}
-	swp_pager_freeswapspace(s_free, n_free);
-
 	/*
 	 * Free left over swap blocks in source.
 	 *
@@ -2003,31 +1999,30 @@ allocated:
 }
 
 /*
- * SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
+ * SWP_PAGER_META_TRANSFER() - free a range of blocks in the srcobject's swap
+ * metadata, or transfer it into dstobject.
  *
- *	The requested range of blocks is freed, with any associated swap
- *	returned to the swap bitmap.
- *
  *	This routine will free swap metadata structures as they are cleaned
- *	out.  This routine does *NOT* operate on swap metadata associated
- *	with resident pages.
+ *	out.
  */
 static void
-swp_pager_meta_free(vm_object_t object, vm_pindex_t pindex, vm_pindex_t count)
+swp_pager_meta_transfer(vm_object_t srcobject, vm_object_t dstobject,
+    vm_pindex_t pindex, vm_pindex_t count)
 {
 	struct swblk *sb;
 	daddr_t n_free, s_free;
-	vm_pindex_t last;
+	vm_pindex_t offset, last;
 	int i, limit, start;
 
-	VM_OBJECT_ASSERT_WLOCKED(object);
-	if (object->type != OBJT_SWAP || count == 0)
+	VM_OBJECT_ASSERT_WLOCKED(srcobject);
+	if (srcobject->type != OBJT_SWAP || count == 0)
 		return;
 
 	swp_pager_init_freerange(&s_free, &n_free);
+	offset = pindex;
 	last = pindex + count;
 	for (;;) {
-		sb = SWAP_PCTRIE_LOOKUP_GE(&object->un_pager.swp.swp_blks,
+		sb = SWAP_PCTRIE_LOOKUP_GE(&srcobject->un_pager.swp.swp_blks,
 		    rounddown(pindex, SWAP_META_PAGES));
 		if (sb == NULL || sb->p >= last)
 			break;
@@ -2037,18 +2032,39 @@ swp_pager_meta_free(vm_object_t object, vm_pindex_t pi
 		for (i = start; i < limit; i++) {
 			if (sb->d[i] == SWAPBLK_NONE)
 				continue;
-			swp_pager_update_freerange(&s_free, &n_free, sb->d[i]);
+			if (dstobject == NULL ||
+			    !swp_pager_xfer_source(srcobject, dstobject, 
+			    sb->p + i - offset, sb->d[i])) {
+				swp_pager_update_freerange(&s_free, &n_free,
+				    sb->d[i]);
+			}
 			sb->d[i] = SWAPBLK_NONE;
 		}
 		pindex = sb->p + SWAP_META_PAGES;
 		if (swp_pager_swblk_empty(sb, 0, start) &&
 		    swp_pager_swblk_empty(sb, limit, SWAP_META_PAGES)) {
-			SWAP_PCTRIE_REMOVE(&object->un_pager.swp.swp_blks,
+			SWAP_PCTRIE_REMOVE(&srcobject->un_pager.swp.swp_blks,
 			    sb->p);
 			uma_zfree(swblk_zone, sb);
 		}
 	}
 	swp_pager_freeswapspace(s_free, n_free);
+}
+
+/*
+ * SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
+ *
+ *	The requested range of blocks is freed, with any associated swap
+ *	returned to the swap bitmap.
+ *
+ *	This routine will free swap metadata structures as they are cleaned
+ *	out.  This routine does *NOT* operate on swap metadata associated
+ *	with resident pages.
+ */
+static void
+swp_pager_meta_free(vm_object_t object, vm_pindex_t pindex, vm_pindex_t count)
+{
+	swp_pager_meta_transfer(object, NULL, pindex, count);
 }
 
 /*

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