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

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Date:   Wed, 8 Jul 2020 15:48:04 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     "tiantao (H)" <tiantao6@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Tian Tao <tiantao6@...ilicon.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com
Subject: Re: [PATCH] vmalloc: Removing incorrect logs when vmalloc failed

> > > 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>

--
Vlad Rezki