svn commit: r243631 - in head/sys: kern sys

[Oleksandr Tymoshenko]

On 12/18/2012 1:59 AM, Alan Cox wrote:
> On 12/17/2012 23:40, Oleksandr Tymoshenko wrote:
>> On 2012-12-08, at 1:21 PM, Alan Cox <alc at rice.edu> wrote:
>>
>>> On 12/08/2012 14:32, Andre Oppermann wrote:
>> .. skipped ..
>>
>>>> The trouble seems to come from NSFBUFS which is (512 + maxusers * 16)
>>>> resulting in a kernel map of (512 + 400 * 16) * PAGE_SIZE = 27MB.  This
>>>> seem to be pushing it with the smaller ARM kmap layout.
>>>>
>>>> Does it boot and run when you set the tunable kern.ipc.nsfbufs=3500?
>>>>
>>>> ARM does have a direct map mode as well which doesn't require the
>>>> allocation
>>>> of sfbufs.  I'm not sure which other problems that approach has.
>>>>
>>> Only a few (3?) platforms use it.  It reduces the size of the user
>>> address space, and translation between physical addresses and direct map
>>> addresses is not computationally trivial as it is on other
>>> architectures, e.g., amd64, ia64.  However, it does try to use large
>>> page mappings.
>>>
>>>
>>>> Hopefully alc@ (added to cc) can answer that and also why the kmap of
>>>> 27MB
>>>> manages to wrench the ARM kernel.
>>>>
>>> Arm does not define caps on either the buffer map size (param.h) or the
>>> kmem map size (vmparam.h).  It would probably make sense to copy these
>>> definitions from i386.
>> Adding caps didn't help. I did some digging and found out that although address range
>> 0xc0000000 .. 0xffffffff is indeed valid for ARM in general actual KVA space varies for
>> each specific hardware platform. This "real" KVA is defined by <virtual_avail, virtual_end>
>> pair and ifI use them instead of <VM_MIN_KERNEL_ADDRESS, VM_MAX_KERNEL_ADDRESS>
>> in init_param2 function my pandaboard successfully boots. Since former pair is used for defining
>> kernel_map boundaries I believe it should be used for auto tuning as well.
>
> That makes sense.  However, "virtual_avail" isn't the start of the
> kernel address space.  The kernel map always starts at
> VM_MIN_KERNEL_ADDRESS.  (See kmem_init().)  "virtual_avail" represents
> the next unallocated virtual address in the kernel address space at an
> early point in initialization.  "virtual_avail" and "virtual_end" aren't
> used after that, or outside the VM system.  Please use
> vm_map_min(kernel_map) and vm_map_max(kernel_map) instead.

I checked: kernel_map is not available (NULL) at this point.  So we 
can't use it to
determine real KVA size. Closest thing we can get is 
virtual_avail/virtual_end pair.

Andre, could you approve attached patch for commit or suggest better 
solution?

>
> That said, I would still add caps on the buffer map and kmem map size.
> As memory sizes on arm systems grow, you'll eventually need them, just
> like we did on i386.
What's the names for #defines for these?


-------------- next part --------------
Index: kern/subr_param.c
===================================================================
--- kern/subr_param.c	(revision 244665)
+++ kern/subr_param.c	(working copy)
@@ -333,7 +333,7 @@
 	 * At most it can be 3/4 of available kernel memory.
 	 */
 	realmem = qmin((quad_t)physpages * PAGE_SIZE,
-	    VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS);
+	    virtual_end - virtual_avail);
 	maxmbufmem = realmem / 2;
 	TUNABLE_QUAD_FETCH("kern.maxmbufmem", &maxmbufmem);
 	if (maxmbufmem > (realmem / 4) * 3)
@@ -347,8 +347,8 @@
 	TUNABLE_LONG_FETCH("kern.ipc.maxpipekva", &maxpipekva);
 	if (maxpipekva < 512 * 1024)
 		maxpipekva = 512 * 1024;
-	if (maxpipekva > (VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS) / 64)
-		maxpipekva = (VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS) /
+	if (maxpipekva > (virtual_end - virtual_avail) / 64)
+		maxpipekva = (virtual_end - virtual_avail) /
 		    64;
 }