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Date: Thu, 27 Jul 2006 09:07:44 -0400
To: bertrand@toggg.com
Sender: Ilia Alshanetsky <iliaal@gmail.com>
Subject: Re: [PHP-DEV] memory_get_usage with new Memory Manager
From: ilia@prohost.org (Ilia Alshanetsky)


On 27-Jul-06, at 9:03 AM, bertrand Gugger wrote:

> Ilia Alshanetsky wrote:
>> On 27-Jul-06, at 6:02 AM, Matt W wrote:
>>>
>>> Something else I'd like to see changed...  Does anyone think
>>> memory_get_[peak_]usage() should *always* be available,  
>>> regardless of
>>> whether memory_limit is actually enabled?  Using the Windows   
>>> binaries at
>>> least, I was devastated :-D that they were unavailable for   
>>> experimenting,
>>> etc.
>>>
>> Counting memory all the time adds a fair amount of overhead to  
>> script  execution especially given how frequently PHP needs to  
>> allocate  memory. Therefore usage memory utilization functions are  
>> only  available when PHP is compiled with memory in which case it  
>> keeps  track of its mem usage.
>
> That may hear off topic , but how you enable something else than 8M  
> *without* getting this counting overhead ?

Eh? When you set a limit what are you trying to do? From my  
experience most of the time this setting is used by hosting providers  
to restrict memory utilization of various PHP scripts to avoid out-of- 
memory situations and system abuse. As such you'd want as accurate  
measurement as possible including any overhead and what not, since it  
is possible to use the overhead to exceed or in some cases even to  
bypass the memory limit entirely.

> It looks to me that --enable-memory-limit mixes 2 independant roles :
> - setting the amount of available memory, and enabling eventually  
> local setting,
> - enabling the evaluation of the process consumption.

That is correct. Memory limit by its nature requires PHP to count the  
amount of memory consumed, since such tracking is performed it  
enabled PHP to report internally via functions (or via Apache log)  
about its memory utilization.

Ilia Alshanetsky