Re: [PHP-DEV] PHP4: php_module holds memory to long !

[Bill Stoddard]

  Any ideas ?

 Welcome to Unix.  You can only increase the heap size using
 sbrk(), you cannot shrink it.  So, if you have allocated n
 bytes, you can only reuse those bytes, but never give it back
 to the system (without terminating the process).

 - Sascha

Really?

From AIX docco...
"The sbrk subroutine adds to the break value the number of bytes contained in
the Increment parameter and changes the amount of available space accordingly.
The Increment parameter can be a negative number, in which case the amount of
available space is decreased."

Bill





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Re: [PHP-DEV] PHP4: php_module holds memory to long !

[Stig Venaas]

On Wed, Jan 10, 2001 at 09:23:43PM +0200, Stanislav Malyshev wrote:
 SS Thanks for the correction!  I have never seen that in action
 SS though.  Usually, the C library will keep freed memory in
 SS free lists and does not decrease the size of the data
 SS segment using sbrk.
 
 Actually, from glibc source there's a hook that is supposed to do this in
 some circumstances. Never could actually make it work in real life. Also,
 IIRC glibc on Linux allocates really large (8k+?  16k+?) blocks as mmap's
 of /dev/zero and those are really given back to system, since on free they
 are just munmap'ed.

Checked the glibc 2.2 sources, looks like 128k+ blocks are mmap'ed and
given back to the system.

How does Zend allocate memory then? I guess I could try to figure it
out myself, but it's a bit complex. Are there many small chunks? Seems
like emalloc() is called a lot creating small chunks, but each emalloc()
doesn't result in a corresponding malloc() perhaps? I guess with glibc
on Linux it would be nice if malloc() allocated say 128k chunks, and
emalloc() used memory inside those.

Stig

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Re: [PHP-DEV] PHP4: php_module holds memory to long !

[Filip Sielimowicz]

The answer is really not so easy.
I have RedHat Linux 6.2 (with standard kernel, I suppose 2.1).
I tried such program in c++:

//File mall.cc

#include alloc.h
#include stdio.h
#include stdlib.h
#include unistd.h

int main() {
void* v[1000];
for (int i=0;i1000;i++) {
v[i]=malloc(10);
//printf("%i. %p; ",i,v[i]);
memset(v[i],i,1);
}
printf("\n\nMemory allocated. Wait 20 s.\n");
sleep(20);
for (int i=0;i1000;i++) {
free(v[i]);
//printf("%i. ^; ",i,v[i]);
}
printf("\nMemory freed. Wait 20 s.\n");
sleep(20);

}

Then I examine it with 'top' command (then shift-M to sort by memory
usage).

In first 20 seconds process 'mall' is on the top with 13M, then
in next 20 s it is NOT.

And here is the basic difference between 'mall' and 'httpd' processes: the
last are on the top ALL THE TIME.

So ?


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