From 521a34d33b85e75013656b3dbb333035ed1d8a41 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Mon, 24 Feb 2014 22:42:22 +0100
Subject: [PATCH] kernel: keep cached pages continuous at the end of the page
 list on imagereclaim()

imagereclaim() sabotaged itself by breaking the invariant
that cached pages are kept at the end of the page list.

once we made a hole of uncached pages, we would stop
reclaiming cached pages before it as the loop breaks
once it hits a uncached page. (we iterate backwards from
the tail to the head of the pagelist until pages have been
reclaimed or we hit a uncached page).

the solution is to move pages to the head of the pagelist
after removing them from the image cache.
---
 sys/src/9/port/page.c    | 2 +-
 sys/src/9/port/portfns.h | 1 +
 sys/src/9/port/segment.c | 9 +++++++--
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/sys/src/9/port/page.c b/sys/src/9/port/page.c
index d76fc4038..60cbee12e 100644
--- a/sys/src/9/port/page.c
+++ b/sys/src/9/port/page.c
@@ -64,7 +64,7 @@ pageinit(void)
 	print("%ldM swap\n", vkb/1024);
 }
 
-static void
+void
 pageunchain(Page *p)
 {
 	if(canlock(&palloc))
diff --git a/sys/src/9/port/portfns.h b/sys/src/9/port/portfns.h
index 41b4b105d..96071501c 100644
--- a/sys/src/9/port/portfns.h
+++ b/sys/src/9/port/portfns.h
@@ -202,6 +202,7 @@ int		okaddr(uintptr, ulong, int);
 int		openmode(ulong);
 Block*		packblock(Block*);
 Block*		padblock(Block*, int);
+void		pageunchain(Page*);
 void		pagechainhead(Page*);
 void		pageinit(void);
 ulong	pagenumber(Page*);
diff --git a/sys/src/9/port/segment.c b/sys/src/9/port/segment.c
index cd48d52b4..c73698b9e 100644
--- a/sys/src/9/port/segment.c
+++ b/sys/src/9/port/segment.c
@@ -313,7 +313,7 @@ static void
 imagereclaim(void)
 {
 	int n;
-	Page *p;
+	Page *p, *x;
 	uvlong ticks;
 
 	irstats.calls++;
@@ -329,11 +329,16 @@ imagereclaim(void)
 	 * end of the list (see putpage) so start there and work
 	 * backward.
 	 */
-	for(p = palloc.tail; p && p->image && (n<1000 || !imagealloc.free); p = p->prev) {
+	for(p = palloc.tail; p && p->image && (n<1000 || !imagealloc.free); p = x) {
+		x = p->prev;
 		if(p->ref == 0 && canlock(p)) {
 			if(p->ref == 0 && p->image && !p->image->notext) {
 				n++;
 				uncachepage(p);
+
+				/* move to head to maintain the invariant above */
+				pageunchain(p);
+				pagechainhead(p);
 			}
 			unlock(p);
 		}