Re: superpages in FreeBSD (netmap related) ?

On Monday, June 1, 2015, Marko Zec <zec_at_fer.hr> wrote:

> On Mon, 1 Jun 2015 11:34:00 +0200
> Luigi Rizzo <rizzo_at_iet.unipi.it <javascript:;>> wrote:
>
> > Hi,
> > i was wondering how we can improve the netmap memory allocator
> > to make use of 2M pages (through the page promotion trick).
> >
> > in netmap, when we allocate packet buffers,
> > we issue requests for 4k blocks to contigmalloc(),
> > and i have no idea if there is a way to improve the
> > chance that the memory is mapped to 2M pages ?
>
> In my (previous life) experience, when requested large enough blocks,
> malloc() did a good job at automatically promoting those to superpages,
> and in my applications this behavior was 100% consistent, at least on
> amd64.  After the block is allocated one can check whether it is
> superpage-mapped:
>
> pmap_t pmap = vmspace_pmap(curthread->td_proc->p_vmspace);
>
> if (pmap_mincore(pmap, (vm_offset_t) addr) & MINCORE_SUPER)
>         /* you're good */
> else
>         /* bad luck */


Thanks. Do you know if there is any way to run some equivalente test from
user space ?

Cheers
Luigi


> OTOH I'm not aware of any mechanisms for forcing superpage allocations
> at malloc() time.
>
> Marko
>


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