svn commit: r251586 - head/sys/arm/ti

[Konstantin Belousov]

On Mon, Jun 10, 2013 at 12:02:20PM -0500, Alan Cox wrote:
> On 06/10/2013 06:08, Olivier Houchard wrote:
> > On Mon, Jun 10, 2013 at 06:55:47AM +0300, Konstantin Belousov wrote:
> >> On Sun, Jun 09, 2013 at 10:51:12PM +0000, Olivier Houchard wrote:
> >>> Author: cognet
> >>> Date: Sun Jun  9 22:51:11 2013
> >>> New Revision: 251586
> >>> URL: http://svnweb.freebsd.org/changeset/base/251586
> >>>
> >>> Log:
> >>>   Increase the maximum KVM available on TI chips. Not sure why we suddenly need
> >>>   that much, but that lets me boot with 1GB of RAM.
> >> I suspect that the cause is the combination of limited KVA and
> >> lack of any limitation for the buffer map. I noted that ARM lacks
> >> VM_BCACHE_SIZE_MAX after a report from mav about similar (?) problem a
> >> day ago.
> >>
> >> In essence, the buffer map is allowed to take up to ~330MB when no
> >> upper limit from VM_BCACHE_SIZE_MAX is specified.
> >
> > Hi Konstantin,
> >
> > Thanks for the hint !
> > It seems only i386 and sparc64 sets it, what would be a good value, 200M, as
> > it is on i386 ?
> >
> 
> Since there are many arm platforms with less than 1 GB of kernel virtual
> address (KVA) space, VM_BCACHE_SIZE_MAX should be made to scale down
> from 200 MB with the available KVA space.  See how VM_KMEM_SIZE_MAX is
> currently defined on arm.

In fact, Ithink it does not make much sense to scale the buffer cache up.
It is mostly wasted space now.  As I measured it, on typical load you
have only 10-20% of instantiated buffers mapped.

Alexander Motin reported that he tested the equivalent of the following
change.  With it committed, I think that r251586 could be reverted.

diff --git a/sys/arm/include/param.h b/sys/arm/include/param.h
index 9ffb118..5c738c2 100644
--- a/sys/arm/include/param.h
+++ b/sys/arm/include/param.h
@@ -128,6 +128,11 @@
 #define USPACE_SVC_STACK_BOTTOM		(USPACE_SVC_STACK_TOP - 0x1000)
 #define USPACE_UNDEF_STACK_TOP		(USPACE_SVC_STACK_BOTTOM - 0x10)
 #define USPACE_UNDEF_STACK_BOTTOM	(FPCONTEXTSIZE + 10)
+
+#ifndef VM_BCACHE_SIZE_MAX
+#define	VM_BCACHE_SIZE_MAX	(128 * 1024 * 1024)
+#endif
+
 /*
  * Mach derived conversion macros
  */
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