svn commit: r308691 - in head/sys: cddl/compat/opensolaris/sys cddl/contrib/opensolaris/uts/common/fs/zfs fs/tmpfs kern vm

[Alan Cox]

On 11/18/2016 04:22, Ruslan Bukin wrote:
> On Thu, Nov 17, 2016 at 10:51:40AM -0600, Alan Cox wrote:
>> On 11/16/2016 11:52, Ruslan Bukin wrote:
>>> On Wed, Nov 16, 2016 at 04:59:39PM +0000, Ruslan Bukin wrote:
>>>> On Wed, Nov 16, 2016 at 06:53:43PM +0200, Konstantin Belousov wrote:
>>>>> On Wed, Nov 16, 2016 at 01:37:18PM +0000, Ruslan Bukin wrote:
>>>>>> I have a panic with this on RISC-V. Any ideas ?
>>>>> How did you checked that the revision you replied to, makes the problem ?
>>>>> Note that the backtrace below is not reasonable.
>>>> I reverted this commit like that and rebuilt kernel:
>>>> git show 2fa36073055134deb2df39c7ca46264cfc313d77 | patch -p1 -R
>>>>
>>>> So the problem is reproducible on dual-core with 32mb mdroot.
>>>>
>>> I just found another interesting behavior:
>>> depending on amount of physical memory :
>>> 700m - panic
>>> 800m - works fine
>>> 1024m - panic
>> I think that this behavior is not inconsistent with your report of the
>> system crashing if you enabled two cores but not one.  Specifically,
>> changing the number of active cores will slightly affect the amount of
>> memory that is allocated during initialization.
>>
>> There is nothing unusual in the sysctl output that you sent out.
>>
>> I have two suggestions.  Try these in order.
>>
>> 1. r308691 reduced the size of struct vm_object.  Try undoing the one
>> snippet that reduced the vm object size and see if that makes a difference.
>>
>>
>> @@ -118,7 +118,6 @@
>>  	vm_ooffset_t backing_object_offset;/* Offset in backing object */
>>  	TAILQ_ENTRY(vm_object) pager_object_list; /* list of all objects of this pager type */
>>  	LIST_HEAD(, vm_reserv) rvq;	/* list of reservations */
>> -	struct vm_radix cache;		/* (o + f) root of the cache page radix trie */
>>  	void *handle;
>>  	union {
>>  		/*
>>
>>
>> 2. I'd like to know if vm_page_scan_contig() is being called.
>>
>> Finally, to simply the situation a little, I would suggest that you
>> disable superpage reservations in vmparam.h.  You have no need for them.
>>
>>
> I made another one merge from svn-head and problem disappeared for 700m,1024m of physical memory, but now I able to reproduce it with 900m of physical memory.
>
> Restoring 'struct vm_radix cache' in struct vm_object gives no behavior changes.
>
> Adding a panic() call to vm_page_scan_contig gives an original panic (so vm_page_scan_contig is not called),
> it looks like size of function is changed and it unhides the original problem.
>
> Disable superpage reservations changes behavior and gives same panic on 1024m boot.

I would still encourage you to commit a change disabling reservations in
vmparam.h until support for superpages is added to the riscv pmap.