Re: Strange memory usage reporting

[Jaroslav Kysela]

On Tue, 26 Aug 2003, Jaroslav Kysela wrote:

> On Tue, 26 Aug 2003, [iso-8859-1] Mĺns Rullgĺrd wrote:
> 
> > I was a little surprised to see top tell me this:
> > 
> >   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
> > 10642 mru       11   0 23200  81m 2740 S  0.0 37.0   0:00.07 tcvp              
> > 
> > It didn't make sense that RES > VIRT, so I check /proc/pid/*.  Their
> > contents are below.  Am I missing something?  Note that they are not
> > consistent with the 'top' line above, since they were copied at a
> > different time.  The effect is easily reproducible.  It happens every
> > time I run my music player with using ALSA.
> 
> I have exactly same behaviour with 2.4.21 kernel. It seems that VmRSS
> grows with the mmap2 syscalls although appropriate munmap is called. I'm
> investigating a possible problem with the memory accounting.

Yes, it seems so. The do_no_page() function in mm/memory.c does accounting 
for reserved pages (++mm->rss), but in zap_pte_range() there is a check 
preventing increase the count of freed pages.

Here is a patch for VM gurus to review (for 2.4 kernel, but it should 
apply to 2.6 as well):

===== mm/memory.c 1.57 vs edited =====
--- 1.57/mm/memory.c	Fri Jun 13 18:26:23 2003
+++ edited/mm/memory.c	Tue Aug 26 15:33:28 2003
@@ -1306,7 +1306,8 @@
 	 */
 	/* Only go through if we didn't race with anybody else... */
 	if (pte_none(*page_table)) {
-		++mm->rss;
+		if (!PageReserved(new_page))
+			++mm->rss;
 		flush_page_to_ram(new_page);
 		flush_icache_page(vma, new_page);
 		entry = mk_pte(new_page, vma->vm_page_prot);


						Jaroslav

-----
Jaroslav Kysela <perex@xxxxxxx>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs

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