Re: [PATCH] O_STREAMING - flag for optimal streaming I/O

[Mark Mielke <mark@mark.mielke.cc>]

On Wed, Oct 09, 2002 at 10:33:25AM +0200, Giuliano Pochini wrote:
> > The point of O_STREAMING is one change: drop pages in the pagecache
> > behind our current position, that are free-able, because we know we will
> > never want them.
> Does it drop pages unconditionally ?  What happens if I do a
> streaming_cat largedatabase > /dev/null while other processes
> are working on it ?  It's not a good thing to remove the whole
> cached data other apps are working on.

Anybody could make the cache thrash. I don't see this as an argument against
O_STREAMING (whether explicitly activated, or dynamically activated).

The only extension I would suggest (I don't think the patch did this?) 
is that pages should only be candidates for being forgotten if all
open files associated with the page are O_STREAMING and all seek
points for all open files are beyond the page.

This would allow for a web app, or similar, that was serving the same
document over two different sockets, to provide a compromise between
O_STREAMING and not O_STREAMING where performance would suffer, but
for the common case, where only one person is accessing the file, the
full benefit of O_STREAMING would be realized.

Does the patch allow for mmap() to benefit from O_STREAMING?
"I intend to access this virtual memory range sequentially..."

mark

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