vmem(9) use in Dtrace

[Pedro Giffuni]

On 15/09/2013 2:53 p. m., Davide Italiano wrote:
> On Sun, Sep 15, 2013 at 9:27 PM, Pedro Giffuni <pfg at freebsd.org> wrote:
>> Hi;
>>
>> Just noticed this, in the old DtraceTODO wiki:
>>
>> https://wiki.freebsd.org/DTraceTODO
>>
>> There is mention of some use that Dtrace makes of Solaris's vmem
>> allocator, specifically vmem_create(), vmem_destroy(), vmem_alloc(), and
>> vmem_free(). These functions (not exact but similar ones) have
>> been brought to FreeBSD 10 (r252330).
>>
>> According to opengrok we may just have to uncomment some Solaris
>> code in sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
>>
>
> We need also to provide at least some sort of wrappers for e.g. flags
> passed to vmem_alloc which takes VM_SLEEP in solaris while in FreeBSD
> this is M_WAITOK etc...
>
>> This would reduce differences with the Solaris code but it has
>> to be examined carefully as I think John Birrell had already
>> solved the issue by providing the resource id's natively (kmem).
>>
>> Just thought I would point it out ... It may be that it is not
>> worth spending too much time on it since the existing code should
>> just work.
>>
>
> vmem is designed to be a generic resource allocator. I still need to
> analyze how Dtrace uses it but in general it provides better
> scalability and less fragmentation wrt home-rolled allocators we have
> in the kernel. FWIW, Illumos uses it for several things, e.g. pid/tid
> allocation. It might worth a try.
>


FWIW, the next point in the old DTrace TODO list is that Solaris
has vmem_cache_*. Maybe providing a cache is something that may
be useful in FreeBSD too.

Regards,

Pedro.