linux-kernel - [PATCH v2] mm/vmalloc: clarify why vmap_range

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Message-ID: <20251209-b4-vmalloc-might_alloc-v2-1-2462ba26ead1@google.com>
Date: Tue, 09 Dec 2025 05:44:14 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>, Uladzislau Rezki <urezki@...il.com>
Cc: Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH v2] mm/vmalloc: clarify why vmap_range_noflush() might sleep

The only reason vmap_range_noflush() can sleep is because of pagetable
allocations.

The actual allocation mechanism is arch-specific so might_alloc()
doesn't work here (what GFP flags would be used?). Hence, just add a
comment.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
Changes in v2:
- Switched from might_alloc() to keeping might_sleep() + comment
- Link to v1: https://lore.kernel.org/r/20251208-b4-vmalloc-might_alloc-v1-1-94a9bb8ecb08@google.com
---
 mm/vmalloc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a53c7462671bdd896f95712af71398ffbe22fb80..c23d378dd4446e2784505ec3d5bb9568fb0d3c9a 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -305,6 +305,7 @@ static int vmap_range_noflush(unsigned long addr, unsigned long end,
 	int err;
 	pgtbl_mod_mask mask = 0;
 
+	/* Might allocate pagetables. */
 	might_sleep();
 	BUG_ON(addr >= end);
 

---
base-commit: ecc46e02e0abe025a6e840cba2d647f23fd1d721
change-id: 20251208-b4-vmalloc-might_alloc-754a791e4e10

Best regards,
-- 
Brendan Jackman <jackmanb@...gle.com>