From: Jarek Poplawski

Date: Mon, 2 Feb 2009 08:43:58 +0000
> On Mon, Feb 02, 2009 at 12:18:54AM -0800, David Miller wrote:

quoted text
> > Allocating 4096 or 8192 bytes for a 1500 byte frame is wasteful.

>

> I mean allocating chunks of cached pages similarly to sk_sndmsg_page

> way. I guess the similar problem is to be worked out in any case. But

> it seems doing it on the linear area requires less changes in other

> places.

This is a very interesting idea, but it has some drawbacks:
1) Just like any other allocator we'll need to find a way to

   handle > PAGE_SIZE allocations, and thus add handling for

   compound pages etc.
   And exactly the drivers that want such huge SKB data areas

   on receive should be converted to use scatter gather page

   vectors in order to avoid multi-order pages and thus strains

   on the page allocator.
2) Space wastage and poor packing can be an issue.
   Even with SLAB/SLUB we get poor packing, look at Evegeniy's

   graphs that he made when writing his NTA patches.
Now, when choosing a way to move forward, I'm willing to accept a

little bit of the issues in #2 for the sake of avoiding the

issues in #1 above.
Jarek, note that we can just keep your current splice() copy hacks in

there.  And as a result we can have an easier to handle migration

path.  We just do the page RX allocation conversions in the drivers

where performance really matters, for hardware a lot of people have.
That's a lot smoother and has less issues that converting the system

wide SKB allocator upside down.
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