Re: [RFC]: Support for zero-copy TCP transmit of user space data

Vladislav Bolkhovitin
2008-12-19T17:35:34Z

Andi Kleen, on 12/19/2008 02:27 PM wrote:
> Vladislav Bolkhovitin <vst@vlnb.net> writes:
>> - Although usage of struct page to keep network related pointer might
>> look as a layering violation, it isn't. I wrote in
>> http://lkml.org/lkml/2008/12/15/190 why.
>
> Sorry but extending struct page for this is really a bad idea because
> of the extreme memory overhead even when it's not used (which is a
> problem on distribution kernels) Find some other way to store this
> information. Even for patches with more general value it was not
> acceptable.

Sure, this is why I propose to disable that option by default in
distribution kernels, so it would produce no harm. ISCSI-SCST can work
in this configuration quite well too. People who need both iSCSI target
*and* fast working user space device handlers would simply enable that
option and rebuild the kernel. Rejecting this patch provides much worse
alternative: those people would also have to *patch* the kernel at
first, only then enable that option, then rebuild the kernel. (I'm
repeating it to make sure you didn't miss this my point; it was in the
part of my original message, which you cut out.)