Peter Zijlstra wrote:
Hi Tim,
On Wed, 2007-07-11 at 15:37 -0700, Tim Pepper wrote:
On 7/9/07, Peter Zijlstra <[email protected]> wrote:
Use the read-ahead code to provide hints to page reclaim.
This patch has the potential to solve the streaming-IO trashes my
desktop problem.
It tries to aggressively reclaim pages that were loaded in a strong
sequential pattern and have been consumed. Thereby limiting the damage
to the current resident set.
Interesting...
Would it make sense to tie this into (finally) making
POSIX_FADV_NOREUSE something more than a noop?
We talked about that, but the thing is, if we make the functionality
conditional, nobody will ever use it :-/
So, yes, in a perfect world that would indeed make sense. However since
nobody ever uses these [fm]advise calls,..
So the big question is, does this functionally hurt any workload? If it
turns out it does (which I still doubt) then we might hide it behind
knobs, otherwise I'd like to keep it always on.
Then do what we do for FADV_SEQUENTIAL. With that advice, we double the
readahead window. We're already doing readahead, but we do a lot more
when we have the advice. NOREUSE should put much greater pressure on
the vm to drop these pages quickly, or perhaps simply eliminate the
heuristic evaluation of the access pattern and short-circuit straight to
dropping the pages.
We should be encouraging application writers to actually use things like
fadvise when they can tune things more intelligently than kernel
heuristics can.
-- Chris
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