Mailinglist Archive: opensuse (1239 mails)

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Re: [opensuse] Re: XFS and openSUSE 12.1
Roger Oberholtzer said the following on 06/11/2013 07:16 AM:
* If I close all apps that have a file open on the file system, the
cache use remains.
* If I run the 'sync(1)' command, the cache use remains. I would have
thought that the cache would be freed as there is nothing left to cache.
If not immediately, over a decent amount of time. But this is not the
case.
* Only when I unmount the file system does the cache get freed.
Immediately.

I think you're confusing a cacahe with a write-through buffer.

While *YOU* may know that this is being used in write-only mode, the system doens't. A cacahe supposes (temporal at least) locality of access, that the data may be needed again in a short while and that even if it has been written out (as with 'flush') it may be wanted again shortly.

In addition, what may be cached might not be data, it might be metadata for the file system.

That an unmount clears the cache makes sense; there is nothing more wanted with respect to that drive.

https://en.wikipedia.org/wiki/Cache_%28computing%29
<quote>
In computer science, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere. If requested data is contained in the cache (cache hit), this request can be served by simply reading the cache, which is comparatively faster.
</quote>

and
https://en.wikipedia.org/wiki/Cache_%28computing%29#The_difference_between_buffer_and_cache
<quote>
Buffering, on the other hand, a) serves to reduce the number of transfers for otherwise novel data amongst communicating processes, which serves to amortize overhead involved for several small transfers over fewer, larger transfers .....
</quote>


--
How long did the whining go on when KDE2 went on KDE3?

The only universal constant is change. If a species can not adapt it
goes extinct. That's the law of the universe, adapt or die.
-- Billie Walsh, May 18 2013
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