Autotuning of kern.ipc.shmmaxpgs

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

Hi all,
currently the maximum size of SysV shared memory is limited by a static
MD limit. The attached patch allows platforms to not specify such a
limit. If the kernel config doesn't specify one either, the kernel will
compute a limit on startup based on physmem. Platforms with limited KVA
can also set SHMMAX_AUTO_LIMIT, which places an upper boundary on the
auto-tuned value.

The old limit is too restrictive for desktop and e.g. PostgreSQL users.

Comments? Other platforms that should be added to this list?

The patch is intended for pullup.

Joerg

Index: arch/amd64/include/vmparam.h
===================================================================
RCS file: /home/joerg/repo/netbsd/src/sys/arch/amd64/include/vmparam.h,v
retrieving revision 1.20
diff -u -p -r1.20 vmparam.h
--- arch/amd64/include/vmparam.h        13 Dec 2008 14:07:10 -0000      1.20
+++ arch/amd64/include/vmparam.h        22 Feb 2009 20:03:52 -0000
@@ -105,13 +105,6 @@
 #endif
 
 /*
- * Size of shared memory map
- */
-#ifndef SHMMAXPGS
-#define SHMMAXPGS      2048
-#endif
-
-/*
  * Size of User Raw I/O map
  */
 #define        USRIOSIZE       300
Index: arch/i386/include/vmparam.h
===================================================================
RCS file: /home/joerg/repo/netbsd/src/sys/arch/i386/include/vmparam.h,v
retrieving revision 1.69
diff -u -p -r1.69 vmparam.h
--- arch/i386/include/vmparam.h 13 Dec 2008 14:07:10 -0000      1.69
+++ arch/i386/include/vmparam.h 22 Feb 2009 21:54:29 -0000
@@ -86,13 +86,6 @@
 #define I386_MAX_EXE_ADDR      (USRSTACK - MAXSSIZ)
 
 /*
- * Size of shared memory map
- */
-#ifndef SHMMAXPGS
-#define SHMMAXPGS      2048
-#endif
-
-/*
  * Size of User Raw I/O map
  */
 #define        USRIOSIZE       300
Index: conf/param.c
===================================================================
RCS file: /home/joerg/repo/netbsd/src/sys/conf/param.c,v
retrieving revision 1.59
diff -u -p -r1.59 param.c
--- conf/param.c        12 Nov 2008 14:32:34 -0000      1.59
+++ conf/param.c        22 Feb 2009 20:21:47 -0000
@@ -151,8 +151,10 @@ int        mcllowat = MCLLOWAT;
  * Values in support of System V compatible shared memory.     XXX
  */
 #ifdef SYSVSHM
-#ifndef        SHMMAX
+#if !defined(SHMMAX) && defined(SHMMAXPGS)
 #define        SHMMAX  SHMMAXPGS       /* shminit() performs a `*= PAGE_SIZE' 
*/
+#elif !defined(SHMMAX)
+#define SHMMAX 0
 #endif
 #ifndef        SHMMIN
 #define        SHMMIN  1
@@ -163,14 +165,13 @@ int       mcllowat = MCLLOWAT;
 #ifndef        SHMSEG
 #define        SHMSEG  128
 #endif
-#define        SHMALL  SHMMAXPGS
 
 struct shminfo shminfo = {
        SHMMAX,
        SHMMIN,
        SHMMNI,
        SHMSEG,
-       SHMALL
+       0
 };
 #endif
 
Index: kern/sysv_shm.c
===================================================================
RCS file: /home/joerg/repo/netbsd/src/sys/kern/sysv_shm.c,v
retrieving revision 1.115
diff -u -p -r1.115 sysv_shm.c
--- kern/sysv_shm.c     11 Jan 2009 02:45:53 -0000      1.115
+++ kern/sysv_shm.c     23 Feb 2009 13:39:14 -0000
@@ -973,7 +973,16 @@ shminit(void)
        shm_cv = (void *)((uintptr_t)shmsegs +
            ALIGN(shminfo.shmmni * sizeof(struct shmid_ds)));
 
-       shminfo.shmmax *= PAGE_SIZE;
+       if (shminfo.shmmax == 0) {
+               shminfo.shmmax = physmem / 4 * PAGE_SIZE;
+#ifdef SHMMAX_AUTO_LIMIT
+               if (shminfo.shmmax > SHMMAX_AUTO_LIMIT)
+                       shminfo.shmmax = SHMMAX_AUTO_LIMIT & ~(PAGE_SIZE - 1);
+#endif
+       } else {
+               shminfo.shmmax *= PAGE_SIZE;
+       }
+       shminfo.shmall = shminfo.shmmax / PAGE_SIZE;
 
        for (i = 0; i < shminfo.shmmni; i++) {
                cv_init(&shm_cv[i], "shmwait");