linux-kernel - Re: [PATCH] x86/mm: Check return value from memblock_phys_alloc

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Message-ID: <76fc49d-2c45-e45-60bc-5579cfc72c6@rarity.fan>
Date: Wed, 20 Nov 2024 02:56:31 +0300
From: gldrk <me@...ity.fan>
To: Ingo Molnar <mingo@...nel.org>
cc: Dave Hansen <dave.hansen@...ux.intel.com>, 
    Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
    x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm: Check return value from
 memblock_phys_alloc_range()

> 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@...ity.fan>
---
  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