> In particular, doing a mmap() itself is fairly expensive. It implies a
> lot of bookkeeping, and it also implies a fair amount of mucking around
> with CPU VM issues (TLBs, page tables etc). In short, it can be rather
> expensive.
>
> Due to that expense, things that use mmap() often have a "cache" of
> mappings that they have active. Thet gets rid of one expense, but then
> there is the new expense of maintaining that cache (and it can be a
> fairly costly thing to maintain if you want to doa threaded webserver).
>
> In contrast, a "sendfile()" approach can be extremely light-weight, and
> threads much better because it doesn't imply the same kinds of
> maintenance.
I do not like idea of sendfile, but better proposal already walked
around here, it was something like
int copy_data_from_fd_to_fd( int fd_from, int fd_to, int length )
I think that even implementing this (the naivest possible way) might
give some performance gain becuase now you can copy big block of data
at one system call.
> Now, I'm no NT person, but I suspect that we actually do want to have a
> "sendfile()" kind of thing just because it should be fairly easy to
> implement, and would offer some interesting performance advantages for
> some cases. No, it's not truly generic, but it is useful enough in many
> circustances.
I think that copy_data_from_fd_to_fd (it needs better name) is more
powerfull than sendfile.
Pavel
-- I'm really pavel@atrey.karlin.mff.cuni.cz. Pavel Look at http://atrey.karlin.mff.cuni.cz/~pavel/ ;-).- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu