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

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Message-ID: <c2ca11b4-2802-3353-a9d4-a3108bfc9708@csgroup.eu>
Date:   Sat, 15 Jan 2022 10:07:26 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
CC:     Nicholas Piggin <npiggin@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 0/3] mm: support huge vmalloc mapping on arm64/x86



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(-)
>