kernel: add support for sticky segments (cached, preallocated, never paged)

sys/src/9/port/devproc.c

@@ -138,7 +138,7 @@ Cmdtab proccmd[] = {
 };
 
 /* Segment type from portdat.h */
-static char *sname[]={ "Text", "Data", "Bss", "Stack", "Shared", "Phys", "Fixed", };
+static char *sname[]={ "Text", "Data", "Bss", "Stack", "Shared", "Phys", "Fixed", "Sticky" };
 
 /*
  * Qids are, in path:

sys/src/9/port/devsegment.c

@@ -284,6 +284,8 @@ segmentread(Chan *c, void *a, long n, vlong voff)
 		if((g->s->type&SG_TYPE) == SG_FIXED)
 			snprint(buf, sizeof(buf), "va %#p %#p fixed %#p\n", g->s->base, g->s->top-g->s->base,
 				g->s->map[0]->pages[0]->pa);
+		else if((g->s->type&SG_TYPE) == SG_STICKY)
+			snprint(buf, sizeof(buf), "va %#p %#p sticky\n", g->s->base, g->s->top-g->s->base);
 		else
 			snprint(buf, sizeof(buf), "va %#p %#p\n", g->s->base, g->s->top-g->s->base);
 		return readstr(voff, a, n, buf);
@@ -331,6 +333,20 @@ segmentwrite(Chan *c, void *a, long n, vlong voff)
 				if(!iseve())
 					error(Eperm);
 				g->s = fixedseg(va, len/BY2PG);
+			} else if(cb->nf >= 4 && strcmp(cb->f[3], "sticky") == 0){
+				Segment *s;
+
+				if(!iseve())
+					error(Eperm);
+				s = newseg(SG_STICKY, va, len/BY2PG);
+				if(waserror()){
+					putseg(s);
+					nexterror();
+				}
+				for(; va < s->top; va += BY2PG)
+					segpage(s, newpage(1, nil, va));
+				poperror();
+				g->s = s;
 			} else
 				g->s = newseg(SG_SHARED, va, len/BY2PG);
 		} else

sys/src/9/port/fault.c

@@ -270,6 +270,8 @@ fixfault(Segment *s, uintptr addr, int read)
 			copypage(old, *pg);
 			putpage(old);
 		}
+		/* wet floor */
+	case SG_STICKY:			/* Never paged out */
 		mmuphys = PPN((*pg)->pa) | PTEWRITE | PTEVALID;
 		(*pg)->modref = PG_MOD|PG_REF;
 		break;

sys/src/9/port/portdat.h

@@ -368,6 +368,7 @@ enum
 	SG_SHARED	= 04,
 	SG_PHYSICAL	= 05,
 	SG_FIXED	= 06,
+	SG_STICKY	= 07,
 
 	SG_RONLY	= 0040,		/* Segment is read only */
 	SG_CEXEC	= 0100,		/* Detach at exec */

sys/src/9/port/proc.c

@@ -1595,6 +1595,7 @@ killbig(char *why)
 		case SG_SHARED:
 		case SG_PHYSICAL:
 		case SG_FIXED:
+		case SG_STICKY:
 			continue;
 		}
 		qlock(s);

sys/src/9/port/segment.c

@@ -155,6 +155,7 @@ dupseg(Segment **seg, int segno, int share)
 	case SG_SHARED:
 	case SG_PHYSICAL:
 	case SG_FIXED:
+	case SG_STICKY:
 		goto sameseg;
 
 	case SG_STACK:
@@ -499,6 +500,7 @@ mfreeseg(Segment *s, uintptr start, ulong pages)
 	switch(s->type&SG_TYPE){
 	case SG_PHYSICAL:
 	case SG_FIXED:
+	case SG_STICKY:
 		return;
 	}
 

sys/src/9/port/sysproc.c

@@ -773,6 +773,7 @@ syssegbrk(va_list list)
 		case SG_STACK:
 		case SG_PHYSICAL:
 		case SG_FIXED:
+		case SG_STICKY:
 			error(Ebadarg);
 		default:
 			return ibrk(va_arg(list, uintptr), i);