[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] xen/p2m: fix extra memory regions accounting



On 09/04/2015 09:37 AM, Roger Pau Monnà wrote:
Hello,

El 04/09/15 a les 7.07, Juergen Gross ha escrit:
Could you try the attached patch? It should do the job. It is booting
fine on my laptop, but I think you should try it on the machine with
the memory ranges not at page boundary.


Juergen


extramem.patch


commit 3d0f8aa4d1b4c9c16a81902a197b5d6a77e182a0
Author: Juergen Gross <jgross@xxxxxxxx>
Date:   Thu Sep 3 17:44:04 2015 +0200

     xen: switch extra memory accounting to use pfns

     Instead of using physical addresses for accounting of extra memory
     areas available for ballooning switch to pfns as this is much less
     error prone regarding partial pages.

Thanks for taking care of this! I've tested it on the box that has
non-page aligned memory ranges and it works fine, only a couple of
comments below.

     Reported-by: Roger Pau MonnÃÂ <roger.pau@xxxxxxxxxx>
     Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 7a5d566..aa58bc4 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -90,62 +90,65 @@ static void __init xen_parse_512gb(void)
        xen_512gb_limit = val;
  }

-static void __init xen_add_extra_mem(phys_addr_t start, phys_addr_t size)
+static void __init xen_add_extra_mem(unsigned long start_pfn,
+                                    unsigned long n_pfns)

Not very important, but for type consistency this should probably be
xen_pfn_t instead of unsigned long here and below.

All of the p2m code is using unsigned long for pfns. I wouldn't mind
changing this to use xen_pfn_t instead, but this should be done in a
separate patch. I'll put it on my list.


  {
        int i;

        for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
                /* Add new region. */
-               if (xen_extra_mem[i].size == 0) {
-                       xen_extra_mem[i].start = start;
-                       xen_extra_mem[i].size  = size;
+               if (xen_extra_mem[i].n_pfns == 0) {
+                       xen_extra_mem[i].start_pfn = start_pfn;
+                       xen_extra_mem[i].n_pfns = n_pfns;
                        break;
                }
                /* Append to existing region. */
-               if (xen_extra_mem[i].start + xen_extra_mem[i].size == start) {
-                       xen_extra_mem[i].size += size;
+               if (xen_extra_mem[i].start_pfn + xen_extra_mem[i].n_pfns ==
+                   start_pfn) {
+                       xen_extra_mem[i].n_pfns += n_pfns;
                        break;
                }

I also noticed this with the original code, why isn't there a case to
prepend to an existing region:

if (start_pfn + n_pfns == xen_extra_mem[i].start_pfn) {
     xen_extra_mem[i].n_pfns += n_pfns;
     xen_extra_mem[i].start_pfn = start_pfn;
}

Processing of memory is done from low to high addresses. This case
should never happen. And even if it does, the only downside from
not handling this scenario is wasting an additional table entry.


        }
        if (i == XEN_EXTRA_MEM_MAX_REGIONS)
                printk(KERN_WARNING "Warning: not enough extra memory 
regions\n");

-       memblock_reserve(start, size);
+       memblock_reserve(PFN_PHYS(start_pfn), PFN_PHYS(n_pfns));
  }

[...]

@@ -831,9 +833,11 @@ char * __init xen_memory_setup(void)
                                chunk_size = min(size, mem_end - addr);
                        } else if (extra_pages) {
                                chunk_size = min(size, PFN_PHYS(extra_pages));
-                               extra_pages -= PFN_DOWN(chunk_size);
-                               xen_add_extra_mem(addr, chunk_size);
-                               xen_max_p2m_pfn = PFN_DOWN(addr + chunk_size);
+                               pfn_s = PFN_UP(addr);
+                               n_pfns = PFN_DOWN(addr + chunk_size) - pfn_s;

Should xen_add_extra_mem check for empty ranges and bail out early, or
should the caller make sure it doesn't try to add empty ranges?

IMHO it's easier and cleaner to add the check to xen_add_extra_mem.

This isn't critical at all. Adding an empty range is a nop, as a table
entry is regarded to be not used when n_pfns is 0.


Juergen


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.