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Re: [Xen-devel] [Qemu-devel] [PATCH] increase maxmem before calling xc_domain_populate_physmap

On 12/03/14 09:50, Stefano Stabellini wrote:
On Wed, 3 Dec 2014, Don Slutz wrote:
On 12/03/14 07:20, Stefano Stabellini wrote:
On Wed, 3 Dec 2014, Wei Liu wrote:
On Tue, Dec 02, 2014 at 03:23:29PM -0500, Don Slutz wrote:
            hw_error("xc_domain_getinfo failed");
-    if (xc_domain_setmaxmem(xen_xc, xen_domid, info.max_memkb +
-                            (nr_pfn * XC_PAGE_SIZE / 1024)) <
0) {
+    max_pages = info.max_memkb * 1024 / XC_PAGE_SIZE;
+    free_pages = max_pages - info.nr_pages;
+    real_free = free_pages;
+    if (free_pages > VGA_HOLE_SIZE) {
+        free_pages -= VGA_HOLE_SIZE;
+    } else {
+        free_pages = 0;
+    }
I don't think we need to subtract VGA_HOLE_SIZE.
If you do not use some slack (like 32 here), xen does report:

(d5) [2014-11-29 17:07:21] Loaded SeaBIOS
(d5) [2014-11-29 17:07:21] Creating MP tables ...
(d5) [2014-11-29 17:07:21] Loading ACPI ...
(XEN) [2014-11-29 17:07:21] page_alloc.c:1568:d5 Over-allocation for
5: 1057417 > 1057416
(XEN) [2014-11-29 17:07:21] memory.c:158:d5 Could not allocate order=0
This message is a bit red herring.

It's hvmloader trying to populate ram for firmware data. The actual
amount of extra pages needed depends on the firmware.

In any case it's safe to disallow hvmloader from doing so, it will just
relocate some pages from ram (hence shrinking *mem_end).
That looks like a better solution

I went with a "leave some slack" so that the error message above is not

When a change to hvmloader is done so that the message does not appear during
normal usage, the extra pages in QEMU can be dropped.
Although those messages look like fatal errors, they are not. It is
normal way for hvmloader to operate: firstly it tries to allocate extra
memory until it gets an error, then it continues with normal memory,

void mem_hole_populate_ram(xen_pfn_t mfn, uint32_t nr_mfns)
     static int over_allocated;
     struct xen_add_to_physmap xatp;
     struct xen_memory_reservation xmr;

     for ( ; nr_mfns-- != 0; mfn++ )
         /* Try to allocate a brand new page in the reserved area. */
         if ( !over_allocated )
             xmr.domid = DOMID_SELF;
             xmr.mem_flags = 0;
             xmr.extent_order = 0;
             xmr.nr_extents = 1;
             set_xen_guest_handle(xmr.extent_start, &mfn);
             if ( hypercall_memory_op(XENMEM_populate_physmap, &xmr) == 1 )
             over_allocated = 1;

         /* Otherwise, relocate a page from the ordinary RAM map. */

I think there is really nothing to change there. Maybe we want to make
those warnings less scary.

It was not so much that hvmloader is the one to change (but having it check
for room first might be good), but more that a change to xen would be good
(like changing the wording or maybe only output in debug=y builds, etc.).

Maybe a new XENMEMF to suppress the message?

   -Don Slutz

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