Hi,
On 2012/05/16 14:51, Johannes Weiner wrote:
Hi Nai,
On Wed, May 16, 2012 at 01:25:34PM +0800, nai.xia wrote:
Hi Johannes,
Just out of curiosity(since I didn't study deep into the
reclaiming algorithms), I can recall from here that around 2005,
there was an(or some?) implementation of the "Clock-pro" algorithm
which also have the idea of "reuse distance", but it seems that algo
did not work well enough to get merged? Does this patch series finally
solve the problem(s) with "Clock-pro" or totally doesn't have to worry
about the similar problems?
As far as I understood, clock-pro set out to solve more problems than
my patch set and it failed to satisfy everybody.
The main error case was that it could not partially cache data of a
set that was bigger than memory. Instead, looping over the file
repeatedly always has to read every single page because the most
recent page allocations would push out the pages needed in the nearest
future. I never promised to solve this problem in the first place.
But giving more memory to the big looping load is not useful in our
current situation, and at least my code protects smaller sets of
active cache from these loops. So it's not optimal, but it sucks only
half as much :)
Yep, I see ;)
There may have been improvements from clock-pro, but it's hard to get
code merged that does not behave as expected in theory with nobody
understanding what's going on.
My code is fairly simple, works for the tests I've done and the
behaviour observed so far is understood (at least by me).
OK, I assume that you do aware that the system you constructed with
this simple and understandable idea looks like a so called "feedback
system"? Or in other words, I think theoretically the refault-distance
of a page before and after your algorithm is applied is not the same.
And this changed refault-distance pattern is then feed as input into
your algorithm. A feedback system may be hard(and may be simple) to
analyze but may also work well magically.
Well, again I confess I've not done enough course in this area. Just hope
that my words can help you think more comprehensively. :)
Thanks,
Nai
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