From 93b7cabc813f6facf850e8518fc26d0be69aa5c8 Mon Sep 17 00:00:00 2001
From: alc <alc@FreeBSD.org>
Date: Mon, 4 Jun 2012 03:51:08 +0000
Subject: Various small changes to PV entry management:

Constify pc_freemask[].

pmap_pv_reclaim()
  Eliminate "freemask" because it was a pessimization.  Add a comment about
  the resident count adjustment.

free_pv_entry() [i386 only]
  Merge an optimization from amd64 (r233954).

get_pv_entry()
  Eliminate the move to tail of the pv_chunk on the global pv_chunks list.
  (The right strategy needs more thought.  Moreover, there were unintended
  differences between the amd64 and i386 implementation.)

pmap_remove_pages()
  Eliminate unnecessary ()'s.
---
 sys/i386/xen/pmap.c | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

(limited to 'sys/i386/xen/pmap.c')

diff --git a/sys/i386/xen/pmap.c b/sys/i386/xen/pmap.c
index b5a0f2d..4f123b0 100644
--- a/sys/i386/xen/pmap.c
+++ b/sys/i386/xen/pmap.c
@@ -1929,7 +1929,7 @@ pv_to_chunk(pv_entry_t pv)
 #define	PC_FREE0_9	0xfffffffful	/* Free values for index 0 through 9 */
 #define	PC_FREE10	0x0000fffful	/* Free values for index 10 */
 
-static uint32_t pc_freemask[_NPCM] = {
+static const uint32_t pc_freemask[_NPCM] = {
 	PC_FREE0_9, PC_FREE0_9, PC_FREE0_9,
 	PC_FREE0_9, PC_FREE0_9, PC_FREE0_9,
 	PC_FREE0_9, PC_FREE0_9, PC_FREE0_9,
@@ -1977,7 +1977,7 @@ pmap_pv_reclaim(pmap_t locked_pmap)
 	pv_entry_t pv;
 	vm_offset_t va;
 	vm_page_t free, m, m_pc;
-	uint32_t inuse, freemask;
+	uint32_t inuse;
 	int bit, field, freed;
 
 	PMAP_LOCK_ASSERT(locked_pmap, MA_OWNED);
@@ -2010,7 +2010,6 @@ pmap_pv_reclaim(pmap_t locked_pmap)
 		 */
 		freed = 0;
 		for (field = 0; field < _NPCM; field++) {
-			freemask = 0;
 			for (inuse = ~pc->pc_map[field] & pc_freemask[field];
 			    inuse != 0; inuse &= ~(1UL << bit)) {
 				bit = bsfl(inuse);
@@ -2030,16 +2029,16 @@ pmap_pv_reclaim(pmap_t locked_pmap)
 				TAILQ_REMOVE(&m->md.pv_list, pv, pv_list);
 				if (TAILQ_EMPTY(&m->md.pv_list))
 					vm_page_aflag_clear(m, PGA_WRITEABLE);
+				pc->pc_map[field] |= 1UL << bit;
 				pmap_unuse_pt(pmap, va, &free);
-				freemask |= 1UL << bit;
 				freed++;
 			}
-			pc->pc_map[field] |= freemask;
 		}
 		if (freed == 0) {
 			TAILQ_INSERT_TAIL(&newtail, pc, pc_lru);
 			continue;
 		}
+		/* Every freed mapping is for a 4 KB page. */
 		pmap->pm_stats.resident_count -= freed;
 		PV_STAT(pv_entry_frees += freed);
 		PV_STAT(pv_entry_spare += freed);
@@ -2108,13 +2107,21 @@ free_pv_entry(pmap_t pmap, pv_entry_t pv)
 	field = idx / 32;
 	bit = idx % 32;
 	pc->pc_map[field] |= 1ul << bit;
-	/* move to head of list */
-	TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list);
 	for (idx = 0; idx < _NPCM; idx++)
 		if (pc->pc_map[idx] != pc_freemask[idx]) {
-			TAILQ_INSERT_HEAD(&pmap->pm_pvchunk, pc, pc_list);
+			/*
+			 * 98% of the time, pc is already at the head of the
+			 * list.  If it isn't already, move it to the head.
+			 */
+			if (__predict_false(TAILQ_FIRST(&pmap->pm_pvchunk) !=
+			    pc)) {
+				TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list);
+				TAILQ_INSERT_HEAD(&pmap->pm_pvchunk, pc,
+				    pc_list);
+			}
 			return;
 		}
+	TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list);
 	free_pv_chunk(pc);
 }
 
@@ -2178,10 +2185,6 @@ retry:
 				}
 			TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list);
 			TAILQ_INSERT_TAIL(&pmap->pm_pvchunk, pc, pc_list);
-			if (pc != TAILQ_LAST(&pv_chunks, pch)) {
-				TAILQ_REMOVE(&pv_chunks, pc, pc_lru);
-				TAILQ_INSERT_TAIL(&pv_chunks, pc, pc_lru);
-			}
 			PV_STAT(pv_entry_spare--);
 			return (pv);
 		}
@@ -3538,7 +3541,7 @@ pmap_remove_pages(pmap_t pmap)
 	TAILQ_FOREACH_SAFE(pc, &pmap->pm_pvchunk, pc_list, npc) {
 		allfree = 1;
 		for (field = 0; field < _NPCM; field++) {
-			inuse = (~(pc->pc_map[field])) & pc_freemask[field];
+			inuse = ~pc->pc_map[field] & pc_freemask[field];
 			while (inuse != 0) {
 				bit = bsfl(inuse);
 				bitmask = 1UL << bit;
-- 
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