Dan Mick wrote:
Oliver Yang wrote:
Garrett D'Amore wrote:
Oliver Yang wrote:
Hi Guys,
If I use kmem_alloc to alloc a buffer less than 4K, can it ensure
that buffer doesn't cross the page boundary(4k on x86)?
It probably won't cross a page boundary, but the DDI does not
guarantee this.
If you want to provide guarantees like this, use ddi_dma_mem_alloc()
with attributes that specify that page boundaries should not be
crossed.
Yes, I knew. On the man page of kmem_alloc, it just ensures memory is
at least double-word aligned, and no other guarantees.
But I really want to know whether current implementation of
kmem_alloc or slab can guarantees this, if the request alloc size is
less than 4k.
Since not only one guys told me, that is true.
1) so read the source.
2) why do you "really want" to know this? knowing it is useless, as
it is *not guaranteed*, which means it can change at any time.
Yes, I understand that we should not let our code has this kind of wrong
assumption.
A NIC driver who supports LSO will run into hang state if the TCP header
cross the 4k page boundary.
Although the TCP packet is NOT actually allocated by the kmem_alloc, but
it comes from esballoc which should be similar with kmem_alloc.
On most regular NIC hardwares, this will not cause the issue. But in
this LSO special cases, hardware doesn't allow the tcp header cross the
multiple DMA cookies.
I just want to know whether this issue is only happened in that TPC
packet is large than 4K case, or it happend for all the cases.
_______________________________________________
opensolaris-code mailing list
opensolaris-code@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/opensolaris-code
