On Mar 8, 2006, at 12:52 PM, Eugene wrote:
With Apache stopped, it goes down to RSS=0.5GB and VSZ=0.6G --
but Inactive
Memory remains above 2.5GB.
Is it a memory leak somewhere or what?
That looks quite normal to me, apart from the zombie process.
FreeBSD always
attempts to occupy most of the RAM, because it's a very fast way
of saving
information, and after all a lot of RAM is of no use if there's
nothing in
it. So long as no other program needs it for more "important"
information,
there's nothing wrong with keeping a lot of "unimportant" stuff
around in
case it is needed again quickly.
Ok, that's nice. However, I was concerned not so much with low Free
memory as with Act+Inact being 1.5-4 times greater than size of
running processes. What data is there, exactly? I don't think it
has more than 1GB of unsynced disk writes?
No. It's caching all of the pages used by processes which have not
needed to be paged out yet. The syncer process will regularly flush
dirty pages to disk, so the amount of unsynced disk writes is going
to be much smaller.
Also, a more general question: how do I estimate 'real' memory
load? Sum(RSS) + 0.5*DiskCache ?
For example, I would like to know (in advance) e.g. how many Apache
processes we can handle before memory becomes a problem.
The instantaneous 'real' memory load is the Active column, plus the
KVA (wired down memory) and the disk cache. You can divide the
amount of (inactive + free) by the size of each apache httpd, and get
an upper bound on the number of extra httpd's you can probably run.
Paying attention to your page fault rate is a better way of tuning,
however.
Do you think it would be nice if top(1) could give some
consolidated measure -- probably taking into account usage
statistics and/or response time?
Top already attempts to give useful measurements.
Or at least two measures -- e.g. "How much memory can be allocated
off-hand without any disk I/O"
You can allocate an almost unlimited amount of memory, so long as you
don't actually write to it; FreeBSD uses VM overcommit extensively.
and "How much memory can be allocated so that swapped data would
not have to be re-read again in reasonable time"?
That's the "inactive" entry in top, more or less.
--
-Chuck
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