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

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Message-ID: <DESNXS1K25LW.2E7ZWFWV56PZD@google.com>
Date: Mon, 08 Dec 2025 07:39:39 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Anshuman Khandual <anshuman.khandual@....com>, Brendan Jackman <jackmanb@...gle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Uladzislau Rezki <urezki@...il.com>
Cc: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/vmalloc: clarify why vmap_range_noflush() might sleep

Hi Anshuman, thanks a lot for taking a look.

On Mon Dec 8, 2025 at 6:41 AM UTC, Anshuman Khandual wrote:
> Please add <asm-generic/pgalloc.h> in mm/vmalloc.c - otherwise it does not
> get built as GFP_PGTABLE_KERNEL is not available. But otherwise LGTM.

Oh, but that's not correct, IIUC we shouldn't directly be including
asm-generic headers from here.

So while in principle GFP_PGTABLE_KERNEL is a sensible common
demoninator here, it doesn't actually exist at all everywhere, e.g. it
doesn't look like m68k defines it for Motorola. 

So maybe the best way here is a really vague:

/* 
 * Different archs allocate pagetables in different ways, assume
 * GFP_KERNEL as a common denominator.
 */
might_alloc(GFP_KERNEL)

... a bit yucky but I think still useful.

Any thoughts?