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From Jeff Trawick <traw...@gmail.com>
Subject Fwd: [PROOF-OF-CONCEPT?] logging memory used by an allocator
Date Tue, 03 Aug 2004 21:30:42 GMT
---------- Forwarded message ----------
From: Jeff Trawick <trawick@gmail.com>
Date: Tue, 3 Aug 2004 14:45:16 -0400
Subject: Re: [PROOF-OF-CONCEPT?] logging memory used by an allocator
To: Sander Striker <striker@apache.org>

On Sun, 1 Aug 2004 19:46:14 +0200, Sander Striker <striker@apache.org> wrote:
> > From: Jeff Trawick [mailto:trawick@attglobal.net]
> > Sent: Wednesday, July 28, 2004 1:33 PM
> > To: dev@apr.apache.org; dev@httpd.apache.org
> > Subject: [PROOF-OF-CONCEPT?] logging memory used by an allocator
> >
> > A couple of questions come up from an application perspective:
> >
> > am I leaking memory?  if so, on what operation?
> > how much memory does it take to perform a certain operation?
> >
> > If the application can find out how much heap memory is
> > presently owned by a certain allocator, it can be easier to
> > address such questions.
>
> Wouldn't you want to know the memory currently being held by
> the allocator as well as all the memory the allocator dished
> out to it's pools?

I'm sure that could be useful to some folks; I can't think of a use at
the present with Apache unless some logging of the allocator shows
that some request uses a bunch of memory, and we know that there are
various pools in use on that request so we add some temporary debug
code to add pool granularity to the measurement

> > The attached apr.patch adds apr_allocator_memsize_get() to
> > find the amount of heap memory presently owned by the
> > allocator.  (debug pool flavor not implemented; what is
> > implemented isn't tested much ;) )
>
> Given that memory management is on the critical path we need
> to be careful what we add.  But this patch seems pretty harmless
> in that respect.

but doesn't "memsize_get" suck as a name?  any better ideas?

> > The attached httpd.patch adds %Z log format to mod_log_config
> > to log the memory size of the allocator used by the request
> > pool.  (I would lean towards implementing this feature in a
> > debug module instead of in mod_log_config.)
>
> I assume you implemented this because of an itch? :)

biggest itch was, in the context of a suspected storage leak, wanting
to draw a line between Apache memory use and some potential
third-party module or library issue; hard without some such
measurements to even understand the normal Apache storage growth in a
threaded server as more and more threads in the process eventually
handle expensive requests

more specifically:

good for a *rough* idea of memory requirements; I haven't a clue how
much heap memory it takes to process some request; 10K?  100K?

good for determining when it is useful to use MaxMemFree by
identifying situations where an infrequent request takes a lot more
pool memory than normal to process; in such case, it is practical to
set MaxMemFree to approximately the "normal" amount of memory
required, since malloc()/free() overhead won't be a killer

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