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SubjectRe: [PATCH] zero^H^H^H^Hsingle copy pipe
On Mon, 7 May 2001, Manfred Spraul wrote:

> The main problem is that map_user_kiobuf() locks pages into memory.
> It's a bad idea for pipes. Either we must severely limit the maximum
> amount of data in the direct-copy buffers, or we must add a swap file
> based backing store. If I understand the BSD direct-pipe code correctly
> it has a swap file based backing store. I think that's insane. And
> limiting the direct copy buffers to a few kB defeats the purpose of
> direct copy.

Okay, how about the following instead (I'm thinking of generic code that
we can reuse): continue to queue the mm, address, length tuple (I've
actually got use for this too), and then use a map_mm_kiobuf (which is
map_user_kiobuf but with an mm parameter) for the portion of the buffer
that's currently being copied. That improves code reuse and gives us a
few primatives that are quite useful elsewhere.

> And the current pipe_{read,write} are a total mess with nested loops and
> gotos. It's possible to create wakeup storms. I rewrote them as well ;-)

Cool! =)

-ben

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