RE: [Xen-devel] RE:2Gb Memory lost in 2.6.32.36 - 50G memory, maxmem=50G, 2G used for pagetable, clamping (max:5G) is not helping.

[MaoXiaoyun <tinnycloud@xxxxxxxxxxx>]

Hi Konrad:
 
     I think I've located where the lost memory going. It is in bootmem when called sparse_init();
 
    I enabled bootmem_debug=1 in kernel start args, and log every __reserve and __free memory with 'count' taged.
 
    Like ___free & __reserve code(end of mail) :
 
    Attached is the output log.
   
1) We give dom0 5630M, that is 5630 * 1024 /4 = 1441280 pages
 
2) Line 204-237 is the stage of early reservations. 
Add up memory in *early reservations* except adderss beyond 15ffe0(line 228) :
     6329(line 225) + 23 + 1508 + 23470 = 31330 pages ( 123M)
 
3) I will caculated the mem reserved after line 237.
 
In line 237 , tot_res_pages is 11631467 and line 1162, its values is  11881636, so 11881636 - 11631467 = 250169 pages are reserved.
In line 203, tot_free_pages is 12776995 and line 1158, its values is 12810787, so 12810787 - 12776995  = 33792 pages are freed
So 250169  - 33792 = 216377 pages (216377 *4 / 1024 =  845M) are still in bootmem, I've been located it is in sparse_init.
 
4) Line 162, 196361 ( 768M )  pages of unused memory are been relesed to Xen.
 
5) Line 1169 ,  Memory is 3717504k =  3630M ,  3630 + 768 + 845 + 123 = 5366.        5630 - 5366 = 264 M (Did I miscaulated? )
  
Questions
 
1) Normally, sparse_init will only reserver about 173M in previous kernel, and in .36 is it meant to reserve so much?
2) where is 264M memory I last caculated, did I make mistake?
 
Many thanks.
 
 
 
 
 
 
 
 
============================code to log========mm/bootmem.c====
 
253 static void __init __free(bootmem_data_t *bdata,
254 <+++<+++<+++unsigned long sidx, unsigned long eidx)
255 {
256 <+++unsigned long idx;
257     static int count;
258     static int tot_free_pages;
259
260     tot_free_pages += (eidx - sidx);
261
262 <+++bdebug("count %d nid=%td start=%lx end=%lx pages %d tot_free_pages %d\n", ++count, bdata - bootmem_node_data,
263 <+++<+++sidx + bdata->node_min_pfn,
264 <+++<+++eidx + bdata->node_min_pfn,
265         eidx - sidx,
266         tot_free_pages
267         );
268
 
277 static int __init __reserve(bootmem_data_t *bdata, unsigned long sidx,
278  unsigned long eidx, int flags)
279 {
280     unsigned long idx;
281     int exclusive = flags & BOOTMEM_EXCLUSIVE;
282     static int count;
283     static int tot_res_pages;
284
285     tot_res_pages += (eidx - sidx);
286 <+++bdebug("count %d nid=%td start=%lx end=%lx flags=%x pages=%d, tot_res_pages %d\n",                                                                  
287         ++c ount,
288 <+++<+++bdata - bootmem_node_data,
289 <+++<+++sidx + bdata->node_min_pfn,
290 <+++<+++eidx + bdata->node_min_pfn,
291 <+++<+++flags,
292         eidx - sidx,
293         tot_res_pages
294         );
    
 

 
> Date: Thu, 19 May 2011 12:16:56 -0400
> From: konrad.wilk@xxxxxxxxxx
> To: tinnycloud@xxxxxxxxxxx
> CC: xen-devel@xxxxxxxxxxxxxxxxxxx; jeremy@xxxxxxxx
> Subject: Re: [Xen-devel] RE:2Gb Memory lost in 2.6.32.36 - 50G memory, maxmem=50G, 2G used for pagetable, clamping (max:5G) is not helping.
>
> > > What happens if you provide dom0_mem=max:5G to clamp on the size?
> > >
> >
> > Seems nothing different(what is clamp means? ^_^ )
>
> http://en.wikipedia.org/wiki/Clamp_(tool)
>
> .. snip..
> > Xen: 0000000100000000 - 0000000c6ff09000 (usable)
> > DMI present.
> > AMI BIOS detected: BIOS may corrupt low RAM, working around it.
> > last_pfn = 0xc6ff09 max_arch_pfn = 0x400000000
> .. snip..
> > xen_commandline : msi=1 iommu=off x2apic=off console=com1,vga com1=115200,8n1 noreboot dom0_mem=max:5G dom0_max_vcpus=4 dom0_vcpus_pin cpuidle=0 cpufreq=none xsave=0
>
> OK, I would have expected your last entry in the E820 to be truncated
> to 15fe00000, but it is not with the max:5G parameter. Looks like
> you found a bug - but I am not sure if it is the Xen hypervisor or
> the E820 parsing code in Linux. Fortunatly for you, I just got my hands on 32G
> machine so I can work on this. Can you remind me in a week if I you do
> not see any patches from me?

2.6.32.36.txt
Description: Text document

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