Re: [PATCH v2 0/3] mm: support huge vmalloc mapping on arm64/x86

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Kefeng Wang <wangkefeng.wang@huawei.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v2 0/3] mm: support huge vmalloc mapping on arm64/x86
Date: Sat, 15 Jan 2022 10:07:26 +0000	[thread overview]
Message-ID: <c2ca11b4-2802-3353-a9d4-a3108bfc9708@csgroup.eu> (raw)
In-Reply-To: <20211227145903.187152-1-wangkefeng.wang@huawei.com>

Le 27/12/2021 à 15:59, Kefeng Wang a écrit :
> Huge vmalloc mappings is supported on PPC[1], but this feature should
> be not only used on PPC, it could be used on arch support HAVE_ARCH_HUGE_VMAP
> and PMD sized vmap mappings. this patchset is to enable this feature
> on arm64/x86.
> 
> There are some disadvantages about this feature[2], one of the main

There are some disadvantage, ok, so are there advantages as well ?

> concerns is the possible memory fragmentation/waste in some scenarios,
> also archs must ensure that any arch specific vmalloc allocations that
> require PAGE_SIZE mappings(eg, module alloc with STRICT_MODULE_RWX)
> use the VM_NO_HUGE_VMAP flag to inhibit larger mappings.
> 
> Based on the above considerations, we add the first patch is to let
> user to control huge vmalloc mapping default behavior.  Meanwhile,
> add new kernel parameter hugevmalloc=on/off to enable/disable this
> feature at boot time, nohugevmalloc parameter is still supported.
> 
> The later two patches to enable this feature on arm64/x86, select
> HAVE_ARCH_HUGE_VMALLOC and mark VM_NO_HUGE_VMAP in arch's module_alloc().
> 
> This patchset based on next-20211224.
> 
> v2:
> - Default y for HUGE_VMALLOC_DEFAULT_ENABLED, not only select it on PPC
> - Fix copy/type error
> - Mark VM_NO_HUGE_VMAP in module_alloc() on arm64/x86
> 
> [1] https://lore.kernel.org/linux-mm/20210317062402.533919-1-npiggin@gmail.com/
> [2] https://lore.kernel.org/linux-mm/1616036421.amjz2efujj.astroid@bobo.none/
> 
> Kefeng Wang (3):
>    mm: vmalloc: Let user to control huge vmalloc default behavior
>    arm64: Support huge vmalloc mappings
>    x86: Support huge vmalloc mappings
> 
>   .../admin-guide/kernel-parameters.txt          | 14 +++++++++++++-
>   arch/arm64/Kconfig                             |  1 +
>   arch/arm64/kernel/module.c                     |  5 +++--
>   arch/x86/Kconfig                               |  1 +
>   arch/x86/kernel/module.c                       |  4 ++--
>   mm/Kconfig                                     |  8 ++++++++
>   mm/vmalloc.c                                   | 18 +++++++++++++++++-
>   7 files changed, 45 insertions(+), 6 deletions(-)
> 