Re: [Wireshark-bugs] [Bug 9114] Memory not released when starting a new capture w/o saving last capture

[Evan Huus <eapache () gmail com>]

On 2013-09-20, at 4:40 PM, Joerg Mayer <jmayer () loplof de> wrote:

> I'd like to discuss the consequences of the remark below in a bit more depth:
>
> On Fri, Sep 20, 2013 at 08:27:47PM +0000, bugzilla-daemon () wireshark org wrote:
> > https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=9114
> ...
> > --- Comment #1 from Jeff Morriss <jeff.morriss.ws () gmail com> ---
> > Wireshark intentionally does not free all the memory it had allocated when
> > closing a capture file.  It uses its own memory allocator which allows it to
> > keep (rather large) blocks of memory around for later re-use (when that happens
> > the memory allocator marks all the memory as "freed" but you won't be able to
> > see that from any OS utilities: they will simply report Wireshark has still
> > having allocated however much memory).  Not freeing that memory is an
> > optimization to avoid having to re-allocate that memory again when the next
> > file is read.
>
> It this really the right strategy? If I open a huge capture file (with huge
> allocations) and then open a small file, the (virtual) memory will still be gone.
> How big is the performance win of not freeing/allocating in real operation?

This is one of the things I looked into with wmem. The performance benefit of not releasing the packet pool between 
each packet is fairly significant. The performance of releasing the file pool between files is not. Wmem memory is 
fully released when closing a file.

If wmem memory is not being freed when closing a file, that is an actual leak.

> thanks
>   Jörg
>
> -- 
> Joerg Mayer                                           <jmayer () loplof de>
> We are stuck with technology when what we really want is just stuff that
> works. Some say that should read Microsoft instead of technology.
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