linux-kernel - Re: [PATCH] vmalloc: Removing incorrect logs when vmalloc failed

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Date:   Thu, 9 Jul 2020 09:03:13 +0800
From:   "tiantao (H)" <tiantao6@...wei.com>
To:     Uladzislau Rezki <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Anshuman Khandual <anshuman.khandual@....com>,
        Tian Tao <tiantao6@...ilicon.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>
Subject: Re: [PATCH] vmalloc: Removing incorrect logs when vmalloc failed



在 2020/7/8 21:48, Uladzislau Rezki 写道:
>>>> On 07/07/2020 02:43 PM, Tian Tao wrote:
>>>>> It is not possible to increase size with vmalloc=<size> in arm64
>>>>> architecture and it will mislead.however vmalloc return failure
>>>>> is a rare occurrence in 'many architectures including arm64'.
>>>>
>>>> But there is a chance that vmalloc() might work on architectures
>>>> that support 'vmalloc=' command line i.e after a change and this
>>>> information here might be helpful in those cases.
>>>>
>>> Agree. At least i see a few users of it:
>>>
>>> <snip>
>>> urezki@...38:~/data/coding/linux-next.git$ grep -rn early_param ./arch/ | grep vmalloc
>>> ./arch/arm/mm/mmu.c:1152:early_param("vmalloc", early_vmalloc);
>>> ./arch/unicore32/mm/mmu.c:276:early_param("vmalloc", early_vmalloc);
>>> ./arch/x86/mm/pgtable_32.c:86:early_param("vmalloc", parse_vmalloc);
>>> urezki@...38:~/data/coding/linux-next.git$
>>> <snip>
>>>
>> I'm actually having this problem with the arm64 architecture at centos 7.6
>> and pagesize is 64K.
>> I followed the prompts and added vmalloc=<size> to the command to increase
>> the size of the vmalloc.and found out it's not worked.
>> It took me some time to find out that this doesn't work for the arm64
>> architecture, so this log is misleading on arm64.
>>
> Agree, it can take time to understand some code or logic behind of it.
> So in that case having good documentation or comments always help.
> 
>> I think it's better not to be prompted than to be prompted incorrectly.
>> I'm sure there will be others with similar problems.
>> So I'd like to solve this problem this time, Please help me with your
>> suggestions.
>> If I change the PATCH to the following, will you accept it?
>>
> Actually it is not up to me to decide what to take or not. Andrew Morton
> is the key person here :) I can just review or make some comments same
> as others.
> 
>>        if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit())
>> +#ifdef CONFIG_ARM64 && CONFIG_XXX
>> +        pr_warn("vmap allocation for size %lu failed\n", size);
>> +#else
>>            pr_warn("vmap allocation for size %lu failed: use vmalloc=<size>
>> to increase size\n",
>>                size);
>> +#endif
>>
> I do not have a strong opinion here, but counting arches seems odd.
> Maybe modify the string with following message:
> 
> <snip>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 1f46c3b86f9f..0aa26bc128d7 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1202,7 +1202,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>          }
>   
>          if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit())
> -               pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size\n",
> +               pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size, if your ARCH supports it\n",
>                          size);
>   
>          kmem_cache_free(vmap_area_cachep, va);
> <snip>
> 
Thanks, that's a good suggestion, I'll send v2 as you suggested!
> --
> Vlad Rezki
> 
> .
>