Re: [Xen-devel] Bootup regression introduced by 7bd0b0f0da3b1ec11cbcc798eb0ef747a1184077 ("memblock: Reimplement memblock allocation using reverse free area iterato") in v3.3-rc0

[Tejun Heo <tj@xxxxxxxxxx>]

Hello,

On Tue, Jan 10, 2012 at 05:45:37PM -0500, Konrad Rzeszutek Wilk wrote:
> (early) [    0.000000] memblock_find: [0x0, 0xfcdd000) size=8409088 
> align=4096 nid=1024
> (early) [    0.000000] memblock_find: [0x805000, 0xfcdd000) - adjusted
> (early) [    0.000000] memblock_find: cand [0x10567000, 0x100000000) -> 
> (early) [0xfcdd000, 0xfcdd000) (early) - rejected
> (early) [    0.000000] memblock_find: cand [0x1e03000, 0x220a000) -> (early) 
> [0x1e03000, 0x220a000) (early) - rejected
> (early) [    0.000000] memblock_find: cand [0x100000, 0x1000000) -> (early) 
> [0x805000, 0x1000000) (early) - rejected
> (early) [    0.000000] memblock_find: cand [0x10000, 0x9b000) -> (early) 
> [0x805000, 0x805000) (early) - rejected
> (early) [    0.000000] Kernel panic - not syncing: Cannot find space for the 
> kernel page tables

So, it actually is a legitimate alloc failure.  It seems I've tried a
bit too hard at simplifying the allocator.  Does the following fix the
problem?

Thanks.

diff --git a/mm/memblock.c b/mm/memblock.c
index 2f55f19..77b5f22 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -106,14 +106,17 @@ phys_addr_t __init_memblock 
memblock_find_in_range_node(phys_addr_t start,
        if (end == MEMBLOCK_ALLOC_ACCESSIBLE)
                end = memblock.current_limit;
 
-       /* adjust @start to avoid underflow and allocating the first page */
-       start = max3(start, size, (phys_addr_t)PAGE_SIZE);
+       /* avoid allocating the first page */
+       start = max_t(phys_addr_t, start, PAGE_SIZE);
        end = max(start, end);
 
        for_each_free_mem_range_reverse(i, nid, &this_start, &this_end, NULL) {
                this_start = clamp(this_start, start, end);
                this_end = clamp(this_end, start, end);
 
+               if (this_end < size)
+                       continue;
+
                cand = round_down(this_end - size, align);
                if (cand >= this_start)
                        return cand;


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