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Subject: Re: [PATCH] mm/hugetlb: suppress wrong warning info when alloc
 gigantic page
To:     Chen Wandun <chenwandun@huawei.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20210219123909.13130-1-chenwandun@huawei.com>
From:   Mike Kravetz <mike.kravetz@oracle.com>
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Date:   Fri, 19 Feb 2021 11:14:00 -0800
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On 2/19/21 4:39 AM, Chen Wandun wrote:
> If hugetlb_cma is enabled, it will skip boot time allocation
> when allocating gigantic page, that doesn't means allocation
> failure, so suppress this warning info.
> 

Normally the addition of warning messages is discouraged.  However, in
this case the additional message provides value.  Why?

Prior to the commit cf11e85fc08c, one could have a kernel command line
that contains:

hugepagesz=1G hugepages=16

This would allocate 16 1G pages at boot time.

After the commit, someone could specify a command line containing:

hugepagesz=1G hugepages=16 hugetlb_cma=16G

In this case, 16G of CMA will be reserved for 1G huge page allocations
after boot time.  The parameter 'hugepages=16' is ignored, and the warning
message is logged.  The warning message should only be logged when the
kernel parameter 'hugepages=' is ignored.

IMO, it make sense to log a warning if ignoring a user specified parameter.
The user should not be attempting boot time allocation and CMA reservation
for 1G pages.

I do not think we should drop the warning as the it tells the user thay
have specified two incompatible allocation options.
-- 
Mike Kravetz


> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
> Signed-off-by: Chen Wandun <chenwandun@huawei.com>
> ---
>  mm/hugetlb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index b6992297aa16..98a49cb9250c 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2465,7 +2465,7 @@ static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
>  		if (hstate_is_gigantic(h)) {
>  			if (hugetlb_cma_size) {
>  				pr_warn_once("HugeTLB: hugetlb_cma is enabled, skip boot time allocation\n");
> -				break;
> +				goto free;
>  			}
>  			if (!alloc_bootmem_huge_page(h))
>  				break;
> @@ -2483,7 +2483,7 @@ static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
>  			h->max_huge_pages, buf, i);
>  		h->max_huge_pages = i;
>  	}
> -
> +free:
>  	kfree(node_alloc_noretry);
>  }
>  
>