Re: [PATCH] x86/mm: Check return value from memblock_phys_alloc_range()

[gldrk]

> Just curious: what type of system has < 4 MiB of contiguous free memory
> available in early boot? Or was it something intentionally constrained
> via qemu?

Yes, I was able to boot a basic Alpine system off virtiofs with a few MiB
total and a stripped-down config.  I happen to have a memory-starved 486
machine that is technically "supported", but it's not running Linux just
yet.

Here's an updated patch.

Signed-off-by: Philip Redkin <me@xxxxxxxxxx>
---
 arch/x86/mm/init.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index eb503f5..6c4ec4f 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -640,8 +640,13 @@ static void __init memory_map_top_down(unsigned long map_start,
 	 */
 	addr = memblock_phys_alloc_range(PMD_SIZE, PMD_SIZE, map_start,
 					 map_end);
-	memblock_phys_free(addr, PMD_SIZE);
-	real_end = addr + PMD_SIZE;
+	if (!addr) {
+		pr_warn("Failed to release memory for alloc_low_pages()");
+		real_end = max(map_start, ALIGN_DOWN(map_end, PMD_SIZE));
+	} else {
+		memblock_phys_free(addr, PMD_SIZE);
+		real_end = addr + PMD_SIZE;
+	}

 	/* step_size need to be small so pgt_buf from BRK could cover it */
 	step_size = PMD_SIZE;
--
2.34.0