linux-kernel - [PATCH v3 2/2] x86/mm: Use GFP_KERNEL for alloc_low

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Message-ID: <92894a9b-3088-4cf7-83bb-ea7382a35d82@neon.tech>
Date: Tue, 10 Jun 2025 11:17:36 +0100
From: Em Sharnoff <sharnoff@...n.tech>
To: linux-kernel@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org
Cc: Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski
 <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
 "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 Oleg Vasilev <oleg@...n.tech>, Arthur Petukhovsky <arthur@...n.tech>,
 Stefan Radig <stefan@...n.tech>, Misha Sakhnov <misha@...n.tech>
Subject: [PATCH v3 2/2] x86/mm: Use GFP_KERNEL for alloc_low_pages() after
 boot

Currently it's GFP_ATOMIC. GFP_KERNEL seems more correct.

>From Ingo M. [1]

> There's no real reason why it should be GFP_ATOMIC AFAICS, other than
> some historic inertia that nobody bothered to fix.

and previously Mike R. [2]

> The few callers that effectively use page allocator for the direct map
> updates are gart_iommu_init() and memory hotplug. Neither of them
> happen in an atomic context so there is no reason to use GFP_ATOMIC
> for these allocations.
>
> Replace GFP_ATOMIC with GFP_KERNEL to avoid using atomic reserves for
> allocations that do not require that.

[1]: https://lore.kernel.org/all/aEE6_S2a-1tk1dtI@gmail.com/
[2]: https://lore.kernel.org/all/20211111110241.25968-5-rppt@kernel.org/

Signed-off-by: Em Sharnoff <sharnoff@...n.tech>
---
Changelog:
- v2: Add this patch
- v3: No changes
---
 arch/x86/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index a2665b6fe376..3a25cd9e9076 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -131,7 +131,7 @@ __ref void *alloc_low_pages(unsigned int num)
 		unsigned int order;

 		order = get_order((unsigned long)num << PAGE_SHIFT);
-		return (void *)__get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
+		return (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
 	}

 	if ((pgt_buf_end + num) > pgt_buf_top || !can_use_brk_pgt) {
-- 
2.39.5