On 2012/05/18 05:08, Johannes Weiner wrote:
On Wed, May 16, 2012 at 08:56:54PM +0800, nai.xia wrote:
On 2012/05/16 14:51, Johannes Weiner wrote:
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.
Damn, that sounded way harsher and arrogant than I wanted it to sound.
And it's only based on what I gathered from the discussions on the
list archives. Sorry :(
No harm done, man. I just understood your words in this way. :)
But I do think that Clock-pro deserves its credit, since after all
it's that research work firstly brought the idea of "refault/reuse
distance" to the kernel community. Further more, it's also good
to let the researchers and the community to together have some
brain-storm of this problem if it's really hard to deal with in
reality.
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.
I'm with you on that, but I can't see an alternative in this case. We
I trend to agree, I once tried to deal with an anti-LRU pattern(e.g. the
big loop like you said) of a app from kernel space and failed. Seems
it's hard to gather a very accurate information of a program's real memory
footprint in mixed workloads with only the help of pte bits...(but also
may due to my lack of skills in tweaking the reclaiming code...)
can't predict future page accesses very well, so we have to take
speculative shots and be considerate about the consequences.
And BECAUSE we may get it wrong, the algorithm does not rely on the
decisions it makes to be correct. For example, it does not activate
pages based on refault distance, but requires the refaulted page to
win the race against an actual active page. Likewise, pages are not
evicted from the active list directly, instead they get a chance at
re-activation when challenged.
Yes. That sounds a smart handling.
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