Re: [Xen-devel] Xen 4.0.1 "xc_map_foreign_batch: mmap failed: Cannot allocate memory"

["Charles Arnold" <carnold@xxxxxxxxxx>]

>>> On 1/6/2011 at 09:50 AM, in message
<alpine.DEB.2.00.1101051748120.2390@kaball-desktop>, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote: 
> On Wed, 5 Jan 2011, Charles Arnold wrote:
>> No, just the usual mmap error.  See the attached logs.
>> 
>> As a reminder, the following conditions exist to duplicate the problem.
>> Host: x86_64 sles11sp1.  Boot with dom0_mem=2048M, set 
>> (enable-dom0-ballooning 
> no) in xend-config.sxp
>> Hypervisor: x86_64 Xen 4.0.1
>> Guests: win2k3 (32bit) and win2k8r2 (64bit)
>> The win2k8r2 guest uses robocopy to copy a 10 Gig file from the win2k3 
> guest.  It copied about 23.2% before failing. 
> 
> (I should have read the subject more carefully)
> 
> xc_map_foreign_batch: mmap failed: Cannot allocate memory
> 
> That is an mmap error on the xch->fd file descriptor.
> Considering that the privcmd mmap implementation sets the vma
> VM_RESERVED | VM_IO | VM_DONTCOPY | VM_PFNMAP and always returns success
> the ENOMEM must come from do_mmap.
> It could be that sysctl_max_map_count has been reached but it is 65530
> by default while the maximum number of buckets in the mapcache on 64
> bits is only 10000.
> Or the kernel could really be out of memory but in that case isn't a
> little strange that we get the error from xc_map_foreign_batch?
> 
> I think we need to add more tracing in the dom0 kernel to figure out
> what the problem is.
> What dom0 kernel are you using?

uname -a
Linux xen86 2.6.32.24-0.2-xen #1 SMP 2010-10-29 16:39:49 +0200 x86_64 x86_64 
x86_64 GNU/Linux
This is sles11sp1.

> Could you add some printk to the kernel source and try again?
> A patch like the following should be enough.

Yes, I'll report back after building and testing.

Thanks,
- Charles

> 
> ---
> 
> 
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index b179abb..3f65277 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -991,16 +991,20 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned 
> long addr,
>  
>       /* Careful about overflows.. */
>       len = PAGE_ALIGN(len);
> -     if (!len)
> +     if (!len) {
> +             printk("DEBUG PAGE_ALIGN ENOMEM\n");
>               return -ENOMEM;
> +     }
>  
>       /* offset overflow? */
>       if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
>                 return -EOVERFLOW;
>  
>       /* Too many mappings? */
> -     if (mm->map_count > sysctl_max_map_count)
> +     if (mm->map_count > sysctl_max_map_count) {
> +             printk("DEBUG too many mappings ENOMEM\n");
>               return -ENOMEM;
> +     }
>  
>       /* Obtain the address to map to. we verify (or select) it and ensure
>        * that it represents a valid section of the address space.
> @@ -1231,14 +1235,18 @@ unsigned long mmap_region(struct file *file, unsigned 
> long addr,
>  munmap_back:
>       vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
>       if (vma && vma->vm_start < addr + len) {
> -             if (do_munmap(mm, addr, len))
> +             if (do_munmap(mm, addr, len)) {
> +                     printk("DEBUG find_vma_prepare ENOMEM\n");
>                       return -ENOMEM;
> +             }
>               goto munmap_back;
>       }
>  
>       /* Check against address space limit. */
> -     if (!may_expand_vm(mm, len >> PAGE_SHIFT))
> +     if (!may_expand_vm(mm, len >> PAGE_SHIFT)) {
> +             printk("DEBUG may_expand_vm ENOMEM\n");
>               return -ENOMEM;
> +     }
>  
>       /*
>        * Set 'VM_NORESERVE' if we should not account for the
> @@ -1259,8 +1267,10 @@ munmap_back:
>        */
>       if (accountable_mapping(file, vm_flags)) {
>               charged = len >> PAGE_SHIFT;
> -             if (security_vm_enough_memory(charged))
> +             if (security_vm_enough_memory(charged)) {
> +                     printk("DEBUG accountable_mapping ENOMEM\n");
>                       return -ENOMEM;
> +             }
>               vm_flags |= VM_ACCOUNT;
>       }
>  
> @@ -1278,6 +1288,7 @@ munmap_back:
>        */
>       vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
>       if (!vma) {
> +             printk("DEBUG kmem_cache_zalloc ENOMEM\n");
>               error = -ENOMEM;
>               goto unacct_error;
>       }



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