On 28.01.2013 20:20, Alan Cox wrote:
On 01/28/2013 08:22, Ian Lepore wrote:
On Mon, 2013-01-28 at 00:09 -0600, Alan Cox wrote:
On Sun, Jan 27, 2013 at 12:11 PM, Ian Lepore <i...@freebsd.org> wrote:
I ran into a panic while attempting to un-tar a large file on a
DreamPlug (arm-based system) running -current. The source and dest of
the un-tar is the root filesystem on sdcard, and I get this:
panic: kmem_malloc(4096): kmem_map too small: 12582912 total allocated
Just before the panic I see the tar process get hung in a "nokva" wait.
12582912 is the value of VM_KMEM_SIZE from arm/include/vmparam.h.
In r245575 the init order for mbuf limits was changed from
SI_SUB_TUNABLES to SI_SUB_KMEM so that mbuf limits could be based on the
results of sizing kernel memory. Unfortunately, the process of sizing
kernel memory relies on the mbuf limits; in kmeminit():
vm_kmem_size = VM_KMEM_SIZE + nmbclusters * PAGE_SIZE;
Since r245575, nmbclusters is zero when this line of code runs. If I
manually plugin "32768" (the number tunable_mbinit() comes up with for
this platform) in that line, the panic stops happening.
So we've got two problems here... one is the circular dependency in
calculating the mbuf limits. The other is the fact that some
non-trivial amount of kernel memory we're allowing for mbufs is actually
being used for other things. That is, if my system was actually using
all the mbufs that tunable_mbinit() allowed for, then this panic while
untarring a huge file would still have happened.
All of this is factually correct. However, it's a red herring. The real
problem is that arm, unlike every other architecture in the tree, does not
enable auto-sizing of the kmem map based on the physical memory size.
Specifically, you'll find VM_KMEM_SIZE_SCALE defined in
"arch"/include/vmparam.h on every other architecture, just not on arm.
This auto-sizing overrides the value of VM_KMEM_SIZE.
Aha. I'll investigate what other architectures do with that and try to
get the same thing going for arm.
i386 or (32-bit) MIPS would be the most similar. Also, I would
encourage you to look for other definitions that those architectures
have that arm doesn't. As physical memory sizes continue to grow on
arm-based systems, they may require other changes in vmparam.h and the
machine-dependent param.h that were made on those other architectures
year ago.
Ian,
The patch below should do the trick. Can you please test?
If you have any questions about any of the definitions, feel free to
e-mail me.
Alan
P.S. When I get a little more free time, I intend to get in touch with
Andre to address the apparent circular dependency. For now just know
that unless that circular dependency is combined with a lack of kmem map
auto-sizing, like arm, it's basically harmless.
I'm working myself through it and will post a patch shortly that untangles
a lot of the obscure VM initialization stuff and moves it into the modern
SYSINIT world.
--
Andre
Index: arm/include/vmparam.h
===================================================================
--- arm/include/vmparam.h (revision 246082)
+++ arm/include/vmparam.h (working copy)
@@ -134,13 +134,16 @@
#endif
#define VM_MAX_KERNEL_ADDRESS 0xffffffff
+
/*
* Virtual size (bytes) for various kernel submaps.
*/
-
#ifndef VM_KMEM_SIZE
-#define VM_KMEM_SIZE (12*1024*1024)
+#define VM_KMEM_SIZE (12*1024*1024)
#endif
+#ifndef VM_KMEM_SIZE_SCALE
+#define VM_KMEM_SIZE_SCALE (2)
+#endif
#define MAXTSIZ (16*1024*1024)
#ifndef DFLDSIZ
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