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SubjectRe: Is sendfile all that sexy?
On Mon, 22 Jan 2001, Helge Hafting wrote:

> And when the next user wants the same webpage/file you read it from
> the RAID again? Seems to me you loose the benefit of caching stuff in
> memory with this scheme. Sure - the RAID controller might have some
> cache, but it is usually smaller than main memory anyway.

Hrm... good point. Using "main memory" (whose memory, on a NUMA box??) as
a cache could be a performance boost in some circumstances. On the other
hand, you're eating up a chunk of memory bandwidth which could be used for
other things - even when you only cache in "spare" RAM, how do you decide
who uses that RAM - and whether or not they should?

There certainly comes a point at which not caching in RAM would be a net
win, but ATM the kernel doesn't know enough to determine this.

On a shared bus, probably the best solution would be to have the data sent
to both devices (NIC and RAM) at once?

> And then there are things like retransmissions...

Hopefully handled by an intelligent NIC in most cases; if you're caching
the file in RAM as well (by "CCing" the data there the first time) this is
OK anyway.

Something to think about, but probably more on-topic for linux-futures I
suspect...


James.

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