Re: superpages in FreeBSD (netmap related) ?
On Mon, 1 Jun 2015 12:11:12 +0200
Luigi Rizzo wrote:
> On Monday, June 1, 2015, Marko Zec wrote:
>
> > On Mon, 1 Jun 2015 11:34:00 +0200
> > Luigi Rizzo > 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 ?
Sure, here's a quickie:
#include
#include
#include
#include
int
main(int argc, char **argv)
{
size_t size, flags, i, super = 0, ordinary = 0;
void *addr;
char *vec;
if (argc != 2)
return (0);
size = atoi(argv[1]);
addr = malloc(size);
vec = malloc(size / 4096);
memset(addr, 0, size);
flags = mincore(addr, size, vec);
printf("addr %p len %d:\n", addr, size);
for (i = 0; i <= size / 4096; i++)
if (vec[i] & MINCORE_SUPER)
super++;
else
ordinary++;
printf("%d 4K blocks super-mapped, %d ordinary 4K pages\n",
super, ordinary);
return (0);
}
x23% ./a.out 100
addr 0x801006000 len 100:
0 4K blocks super-mapped, 245 ordinary 4K pages
x23% ./a.out 1000
addr 0x80100 len 1000:
2048 4K blocks super-mapped, 394 ordinary 4K pages
x23% ./a.out 1000
addr 0x80100 len 1215752192:
296448 4K blocks super-mapped, 367 ordinary 4K pages
The key is that the pages must be touched to be considered for merging
in superpages!
Marko
> Cheers
> Luigi
>
>
> > OTOH I'm not aware of any mechanisms for forcing superpage
> > allocations at malloc() time.
> >
> > Marko
> >
>
>
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Re: superpages in FreeBSD (netmap related) ?
On Monday, June 1, 2015, Marko Zec wrote: > On Mon, 1 Jun 2015 11:34:00 +0200 > Luigi Rizzo > 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 > -- -+--- Prof. Luigi RIZZO, ri...@iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/. Universita` di Pisa TEL +39-050-2217533 . via Diotisalvi 2 Mobile +39-338-6809875 . 56122 PISA (Italy) -+--- ___ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
Re: superpages in FreeBSD (netmap related) ?
On Mon, 1 Jun 2015 11:34:00 +0200 Luigi Rizzo 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 */ OTOH I'm not aware of any mechanisms for forcing superpage allocations at malloc() time. Marko ___ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
