kernel: new pagecache, remove Lock from page, use cmpswap for Ref instead of Lock

make the Page stucture less than half its original size by getting rid of
the Lock and the lru.

The Lock was required to coordinate the unchaining of pages that where
both cached and on the lru freelist.

now pages have a single next pointer that is used for palloc.head
freelist xor for page cache hash chains in Image.pghash[].

cached pages are not on the freelist anymore, but will be reclaimed
from images by the pager when the freelist runs out of pages.

each Image has its own 512 hash chains for cached page lookup. That is
2MB worth of pages and there should be no collisions for most text images.

page reclaiming can be done without holding palloc.lock as the Image is
the owner of the page hash chains protected by the Image's lock.

reclaiming Image structures can be done quickly by only reclaiming pages from
inactive images, that is images which are not currently in use by segments.

the Ref structure has no Lock anymore. Only a single long that is atomically
incremented or decremnted using cmpswap().

there are various other changes as a consequence code. and lots of pikeshedding,
sorry.

1 files changed, 32 insertions, 30 deletions

diff --git a/sys/src/9/port/portdat.h b/sys/src/9/port/portdat.h
index 1d427cfc6..58c82c6a8 100644
--- a/sys/src/9/port/portdat.h
+++ b/sys/src/9/port/portdat.h
@@ -60,7 +60,6 @@ typedef int    Devgen(Chan*, char*, Dirtab*, int, int, Dir*);
 
 struct Ref
 {
-	Lock;
 	long	ref;
 };
 
@@ -151,7 +150,8 @@ struct Block
 
 struct Chan
 {
-	Ref;				/* the Lock in this Ref is also Chan's lock */
+	Ref;
+	Lock;
 	Chan*	next;			/* allocation */
 	Chan*	link;
 	vlong	offset;			/* in fd */
@@ -311,19 +311,16 @@ enum
 
 struct Page
 {
-	Lock;
+	Ref;
+	Page	*next;			/* Free list or Hash chains */
 	uintptr	pa;			/* Physical address in memory */
 	uintptr	va;			/* Virtual address for user */
 	uintptr	daddr;			/* Disc address on swap */
-	ulong	gen;			/* Generation counter for swap */
-	ushort	ref;			/* Reference count */
+	Image	*image;			/* Associated text or swap image */
+	ushort	refage;			/* Swap reference age */
 	char	modref;			/* Simulated modify/reference bits */
 	char	color;			/* Cache coloring */
 	char	cachectl[MAXMACH];	/* Cache flushing control for putmmu */
-	Image	*image;			/* Associated text or swap image */
-	Page	*next;			/* Lru free list */
-	Page	*prev;
-	Page	*hash;			/* Image hash chains */
 };
 
 struct Swapalloc
@@ -340,20 +337,6 @@ struct Swapalloc
 	ulong	xref;			/* Ref count for all map refs >= 255 */
 }swapalloc;
 
-struct Image
-{
-	Ref;
-	long	pgref;			/* number of cached pages (pgref <= ref) */
-	Chan	*c;			/* channel to text file, nil when not used */
-	Qid 	qid;			/* Qid for page cache coherence */
-	ulong	dev;			/* Device id of owning channel */
-	ushort	type;			/* Device type of owning channel */
-	Segment *s;			/* TEXT segment for image if running */
-	Image	*hash;			/* Qid hash chains */
-	Image	*next;			/* Free list */
-	char	notext;			/* no file associated */
-};
-
 struct Pte
 {
 	Page	*pages[PTEPERTAB];	/* Page map for this chunk of pte */
@@ -405,7 +388,7 @@ struct Sema
 struct Segment
 {
 	Ref;
-	QLock	lk;
+	QLock;
 	ushort	steal;		/* Page stealer lock */
 	ushort	type;		/* segment type */
 	uintptr	base;		/* virtual base */
@@ -436,10 +419,29 @@ enum
 };
 #define REND(p,s)	((p)->rendhash[(s)&((1<<RENDLOG)-1)])
 #define MOUNTH(p,qid)	((p)->mnthash[(qid).path&((1<<MNTLOG)-1)])
+#define PGHASH(i,daddr)	((i)->pghash[((daddr)>>PGSHIFT)&(PGHSIZE-1)])
+
+struct Image
+{
+	Ref;
+	Lock;
+	Chan	*c;			/* channel to text file, nil when not used */
+	Qid 	qid;			/* Qid for page cache coherence */
+	ulong	dev;			/* Device id of owning channel */
+	ushort	type;			/* Device type of owning channel */
+	char	notext;			/* no file associated */
+	Segment *s;			/* TEXT segment for image if running */
+	Image	*hash;			/* Qid hash chains */
+	Image	*next;			/* Free list */
+	long	pgref;			/* number of cached pages (pgref <= ref) */
+	Page	*pghash[PGHSIZE];	/* page cache */
+};
+
 
 struct Pgrp
 {
-	Ref;				/* also used as a lock when mounting */
+	Ref;
+	Lock;
 	int	noattach;
 	ulong	pgrpid;
 	QLock	debug;			/* single access via devproc.c */
@@ -449,7 +451,8 @@ struct Pgrp
 
 struct Rgrp
 {
-	Ref;				/* the Ref's lock is also the Rgrp's lock */
+	Ref;
+	Lock;
 	Proc	*rendhash[RENDHASH];	/* Rendezvous tag hash */
 };
 
@@ -476,6 +479,7 @@ struct Evalue
 struct Fgrp
 {
 	Ref;
+	Lock;
 	Chan	**fd;
 	int	nfd;			/* number allocated */
 	int	maxfd;			/* highest fd in use */
@@ -497,13 +501,10 @@ struct Palloc
 {
 	Lock;
 	Pallocmem	mem[4];
-	Page	*head;			/* most recently used */
-	Page	*tail;			/* least recently used */
+	Page	*head;			/* freelist head */
 	ulong	freecount;		/* how many pages on free list now */
 	Page	*pages;			/* array of all pages */
 	ulong	user;			/* how many user pages */
-	Page	*hash[PGHSIZE];
-	Lock	hashlock;
 	Rendez	r;			/* Sleep for free mem */
 	QLock	pwait;			/* Queue of procs waiting for memory */
 };
@@ -772,6 +773,7 @@ extern	Palloc	palloc;
 extern	Queue*	serialoq;
 extern	char*	statename[];
 extern	Image	swapimage;
+extern	Image	fscache;
 extern	char*	sysname;
 extern	uint	qiomaxatomic;
 extern	char*	sysctab[];