code: plan9front

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kernel: implement separate wait queues for page allocation

give kernel processes and local disk file servers (procs
having noswap flag set) a clear advantage for page allocation
under starved condition by giving them ther own wait queue so
they get readied as soon as pages become available.

--- a/sys/src/9/port/page.c

+++ b/sys/src/9/port/page.c

@@ -78,9 +78,12 @@

 	tail->next = palloc.head;

 	palloc.head = head;

 	palloc.freecount += n;

-	if(palloc.r.p != nil)

-		wakeup(&palloc.r);

 	unlock(&palloc);

+

+	if(palloc.pwait[0].p != nil && wakeup(&palloc.pwait[0]) != nil)

+		return;

+	if(palloc.pwait[1].p != nil)

+		wakeup(&palloc.pwait[1]);

 }

 int

@@ -135,10 +138,10 @@

 	return n;

 }

-int

+static int

 ispages(void*)

 {

-	return palloc.freecount >= swapalloc.highwater;

+	return palloc.freecount > swapalloc.highwater || up->noswap && palloc.freecount > 0;

 }

 Page*

@@ -149,26 +152,22 @@

 	int color;

 	lock(&palloc);

-	for(;;) {

-		if(palloc.freecount > swapalloc.highwater)

-			break;

-		if(up->kp && palloc.freecount > 0)

-			break;

+	while(!ispages(nil)){

 		unlock(&palloc);

 		if(s != nil)

 			qunlock(*s);

 		if(!waserror()){

-			eqlock(&palloc.pwait);	/* Hold memory requesters here */

+			Rendezq *q;

+			q = &palloc.pwait[!up->noswap];

+			eqlock(q);	

 			if(!waserror()){

 				kickpager();

-				tsleep(&palloc.r, ispages, 0, 1000);

+				sleep(q, ispages, nil);

 				poperror();

 			}

-

-			qunlock(&palloc.pwait);

-

+			qunlock(q);

 			poperror();

 		}

@@ -182,7 +181,6 @@

 			*s = nil;

 			return nil;

 		}

-

 		lock(&palloc);

 	}

--- a/sys/src/9/port/portdat.h

+++ b/sys/src/9/port/portdat.h

@@ -34,6 +34,7 @@

 typedef struct Queue	Queue;

 typedef struct Ref	Ref;

 typedef struct Rendez	Rendez;

+typedef struct Rendezq	Rendezq;

 typedef struct Rgrp	Rgrp;

 typedef struct RWlock	RWlock;

 typedef struct Sargs	Sargs;

@@ -77,6 +78,12 @@

 	int	locked;		/* flag */

 };

+struct Rendezq

+{

+	QLock;

+	Rendez;

+};

+

 struct RWlock

 {

 	Lock	use;

@@ -506,8 +513,7 @@

 	ulong	freecount;		/* how many pages on free list now */

 	Page	*pages;			/* array of all pages */

 	ulong	user;			/* how many user pages */

-	Rendez	r;			/* Sleep for free mem */

-	QLock	pwait;			/* Queue of procs waiting for memory */

+	Rendezq		pwait[2];	/* Queues of procs waiting for memory */

 	Pallocmem	mem[16];	/* physical user page banks */

 };

--- a/sys/src/9/port/portfns.h

+++ b/sys/src/9/port/portfns.h

@@ -138,7 +138,6 @@

 int		iseve(void);

 int		islo(void);

 Segment*	isoverlap(Proc*, uintptr, uintptr);

-int		ispages(void*);

 int		isphysseg(char*);

 void		ixsummary(void);

 void		kickpager(void);

--- a/sys/src/9/port/swap.c

+++ b/sys/src/9/port/swap.c

@@ -159,7 +159,8 @@

 		up->psstate = "Reclaim";

 		if(reclaim()){

 			up->psstate = "Idle";

-			wakeup(&palloc.r);

+			wakeup(&palloc.pwait[0]);

+			wakeup(&palloc.pwait[1]);

 			sleep(&swapalloc.r, needpages, nil);

 			continue;

 		}