You should take care not to mistake the GC and the MM, they are two different things and surprisingly, they dont interact with each other. Zend GC is a layer above Zend MM, and Zend GC can be totally disabled, Zend MM cant at all.
Zend MM is a BIG layer over malloc()/free() which goals are mainly to abstract the OS MM (mainly Unix/Win32) and to avoid memory fragmentation and too many system calls which could lead to performance problems. Lots of other programms use such a tool, like Apache httpd for example. Zend MM can also help you (in debug mode only) by showing its state after a script has run, alowing you to easily track memory leaks while using it (e**() functions) without the need to use tools such as valgrind. ZendMM can track all the PHP memory usage, and provide feature such as "memory_limit". Finally, ZendMM is a super malloc(), it nearly can be foreseen as a custom implementation of libc malloc() using a heap over the heap and trying to optimize it as possible. Simply looking at the structs in zend_alloc.h let you guess it's goal, but you need to know how memory management works in computer programs for that. Julien.P On Wed, Feb 2, 2011 at 7:52 AM, Adi Mutu <adi_mut...@yahoo.com> wrote: > > Thanks a lot, for all the help about zend mm guys, i'm very grateful. > Thanks,A. > > --- On Sun, 1/30/11, Ben Schmidt <mail_ben_schm...@yahoo.com.au> wrote: > > From: Ben Schmidt <mail_ben_schm...@yahoo.com.au> > Subject: Re: [PHP-DEV] Re: Zend mm > To: "Adi Mutu" <adi_mut...@yahoo.com> > Cc: internals@lists.php.net, t...@daylessday.org > Date: Sunday, January 30, 2011, 4:45 PM > > On 30/01/11 4:11 AM, Adi Mutu wrote: >> I have looked at the sources, but i'm only at the begining of >> analyzing the php sources.....i've understand how to write extensions >> for example, but this memory manager seems more complicated to me..... > > Yes, it is. Memory management is a low-level and subtle area. It takes a > lot of careful thought to design and even to understand the algorithms > involved. It is hard to debug, because an error caused in one place may > not show itself until completely different code is executing. It is also > an area which doesn't change much. Almost all the other code in the PHP > interpreter, and therefore PHP scripts themselves, rely on the memory > manager code doing its job unintrusively and correctly, so once it is > working well, it tends to be left that way, except for fixing small bugs > as they are found, or a big and careful development effort to address > some limitation (e.g. improving the garbage collection to collect > cycles, which was something done fairly recently). > > The bottom line is that this is not an area that is all that easy for > beginners to get their teeth into. But it's also an area that isn't > necessary for beginners to understand in much detail, either. Unless you > have a particular project in mind that involves the memory manager, you > probably don't need to touch it. > > I don't want to discourage you, but just point out that perhaps this is > something you might look at later, or even not at all, as you may find > there are many worthwhile projects that take up all your time before you > ever get to understanding the memory manager fully. > >> It would be useful if for example, could explain me the structures >> that are used in the Zend memory manager, how they're chained >> etc.....and if you can tell me in words what do zend_mm_aloc_int() and >> zend_mm_free_int() basically do...Thank you for your time,Adrian > > I suspect these structures and functions are fairly easy to understand > by someone familiar with the area of memory management, which is why you > have been advised to consult the source code. So perhaps what you need > to do is not learn about PHP's memory manager, but just learn about > memory management in general. Then it should be fairly easy to > understand what PHP's memory manager is doing from its code. > > I'm afraid I doubt the people here have the time to teach you this over > email. :-) So here are some references which might be of use to you. > > - I believe the 'standard textbook' for learning about memory management > is this one here: > http://www.cs.kent.ac.uk/people/staff/rej/gcbook/gcbook.html > > - This page also mentions that a new edition is due out soon: > http://c2.com/cgi/wiki?GarbageCollectionBook > > - You can also check out this site: http://www.memorymanagement.org/ > > - Relating this to, PHP: PHP is a garbage collected language which I > believe uses reference counting and a clever collector to detect and > free cycles. I haven't looked in detail into the implementation, but I > know some documentation is available on the subject here: > http://www.php.net/manual/en/features.gc.php > > Hope this helps! > > Ben. > > > > > > > -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
