Use of contiguous physical memory in cxgbe driver

[Adrian Chadd]

It's about time we taught the physmem allocator to be more conducive
to physically contiguous allocations.

A server with gigabytes of memory should be able to keep a couple tens
of megabytes of 64k sized allocation chunks around for exactly this.



-a


On 22 January 2014 19:45, Garrett Wollman <wollman at freebsd.org> wrote:
> <<On Wed, 22 Jan 2014 16:23:32 -0800, Navdeep Parhar <np at FreeBSD.org> said:
>
>> On 01/22/14 15:52, Garrett Wollman wrote:
>>> At this point everyone is well aware that requiring contiguous
>>> physical page when the hardware can do scatter-gather is a very bad
>>> idea.
>
>> I wouldn't put it this way.  Using buffers with size > PAGE_SIZE has its
>> advantages.
>
> These advantages do not come close to balancing out the disadvantage
> of "your server eventually falls off the network due to physmem
> fragmentation, better hope you can reset it remotely because driving
> in to work at 3 AM sucks."
>
> If any free pages are available at all, the allocation of a 4k jumbo
> mbuf will succeed.  A 9k jumbo mbuf requires three physically
> contiguous pages, and it's very, very easy for physical memory to get
> fragmented to the point where that is impossible.
>
> -GAWollman
>
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