linux-kernel - Re: [PATCH v4 2/3] arm64: Support page mapping percpu first chunk allocator

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Message-ID: <dd6fb4f3-8baa-58b0-d4e9-6852acc82dcf@huawei.com>
Date:   Fri, 17 Sep 2021 15:24:31 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <will@...nel.org>, <catalin.marinas@....com>,
        <ryabinin.a.a@...il.com>, <andreyknvl@...il.com>,
        <dvyukov@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <elver@...gle.com>, <akpm@...ux-foundation.org>,
        <kasan-dev@...glegroups.com>
Subject: Re: [PATCH v4 2/3] arm64: Support page mapping percpu first chunk
 allocator


On 2021/9/17 15:04, Greg KH wrote:
> On Fri, Sep 17, 2021 at 02:55:18PM +0800, Kefeng Wang wrote:
>> On 2021/9/17 14:24, Greg KH wrote:
>>> On Fri, Sep 10, 2021 at 01:33:53PM +0800, Kefeng Wang wrote:
>>>> Percpu embedded first chunk allocator is the firstly option, but it
>>>> could fails on ARM64, eg,
>>>>     "percpu: max_distance=0x5fcfdc640000 too large for vmalloc space 0x781fefff0000"
>>>>     "percpu: max_distance=0x600000540000 too large for vmalloc space 0x7dffb7ff0000"
>>>>     "percpu: max_distance=0x5fff9adb0000 too large for vmalloc space 0x5dffb7ff0000"
>>>> then we could meet "WARNING: CPU: 15 PID: 461 at vmalloc.c:3087 pcpu_get_vm_areas+0x488/0x838",
>>>> even the system could not boot successfully.
>>>>
>>>> Let's implement page mapping percpu first chunk allocator as a fallback
>>>> to the embedding allocator to increase the robustness of the system.
>>>>
>>>> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>>>> ---
>>>>    arch/arm64/Kconfig       |  4 ++
>>>>    drivers/base/arch_numa.c | 82 +++++++++++++++++++++++++++++++++++-----
>>>>    2 files changed, 76 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>>> index 077f2ec4eeb2..04cfe1b4e98b 100644
>>>> --- a/arch/arm64/Kconfig
>>>> +++ b/arch/arm64/Kconfig
>>>> @@ -1042,6 +1042,10 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
>>>>    	def_bool y
>>>>    	depends on NUMA
>>>> +config NEED_PER_CPU_PAGE_FIRST_CHUNK
>>>> +	def_bool y
>>>> +	depends on NUMA
>>> Why is this a config option at all?
>> The config is introduced from
>>
>> commit 08fc45806103e59a37418e84719b878f9bb32540
>> Author: Tejun Heo <tj@...nel.org>
>> Date:   Fri Aug 14 15:00:49 2009 +0900
>>
>>      percpu: build first chunk allocators selectively
>>
>>      There's no need to build unused first chunk allocators in. Define
>>      CONFIG_NEED_PER_CPU_*_FIRST_CHUNK and let archs enable them
>>      selectively.
>>
>> For now, there are three ARCHs support both PER_CPU_EMBED_FIRST_CHUNK
>>
>> and PER_CPU_PAGE_FIRST_CHUNK.
>>
>>    arch/powerpc/Kconfig:config NEED_PER_CPU_PAGE_FIRST_CHUNK
>>    arch/sparc/Kconfig:config NEED_PER_CPU_PAGE_FIRST_CHUNK
>>    arch/x86/Kconfig:config NEED_PER_CPU_PAGE_FIRST_CHUNK
>>
>> and we have a cmdline to choose a alloctor.
>>
>>     percpu_alloc=   Select which percpu first chunk allocator to use.
>>                     Currently supported values are "embed" and "page".
>>                     Archs may support subset or none of the selections.
>>                     See comments in mm/percpu.c for details on each
>>                     allocator.  This parameter is primarily for debugging
>>                     and performance comparison.
>>
>> embed percpu first chunk allocator is the first choice, but it could fails
>> due to some
>>
>> memory layout(it does occurs on ARM64 too.), so page mapping percpu first
>> chunk
>>
>> allocator is as a fallback, that is what this patch does.
>>
>>>> +
>>>>    source "kernel/Kconfig.hz"
>>>>    config ARCH_SPARSEMEM_ENABLE
>>>> diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
>>>> index 46c503486e96..995dca9f3254 100644
>>>> --- a/drivers/base/arch_numa.c
>>>> +++ b/drivers/base/arch_numa.c
>>>> @@ -14,6 +14,7 @@
>>>>    #include <linux/of.h>
>>>>    #include <asm/sections.h>
>>>> +#include <asm/pgalloc.h>
>>>>    struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
>>>>    EXPORT_SYMBOL(node_data);
>>>> @@ -168,22 +169,83 @@ static void __init pcpu_fc_free(void *ptr, size_t size)
>>>>    	memblock_free_early(__pa(ptr), size);
>>>>    }
>>>> +#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
>>> Ick, no #ifdef in .c files if at all possible please.
>> The drivers/base/arch_numa.c is shared by RISCV/ARM64, so I add this config
>> to
>>
>> no need to build this part on RISCV.
> Ok, then you need to get reviews from the mm people as I know nothing
> about this at all, sorry.  This file ended up in drivers/base/ for some
> reason to make it easier for others to use cross-arches, not that it had
> much to do with the driver core :(

Ok, I has Cc'ed Andrew and mm list ;)

Hi Catalin and Will, this patchset is mostly changed for arm64,

and the change itself  is not too big,  could you pick it up from arm64

tree if there are no more comments,  many thanks.

>
> thanks,
>
> greg k-h
> .
>