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Subject: Re: [PATCH] mm/hugetlb: suppress wrong warning info when alloc
 gigantic page
To:     David Hildenbrand <david@redhat.com>,
        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>
 <46e76ac3-def1-80d4-14f1-61f7cd00d033@oracle.com>
 <cf79e9a4-72ba-8fa0-0710-5e82a5b5e4d5@redhat.com>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <2cb384b9-1301-59a8-f678-c67ee26053b3@oracle.com>
Date:   Thu, 4 Mar 2021 09:20:23 -0800
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On 3/4/21 1:35 AM, David Hildenbrand wrote:
> On 19.02.21 20:14, Mike Kravetz wrote:
>> 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.
>>
> 
> I agree. It has value.
> 

Hi David,

Sorry my above reply was too quick as I did not take a close look at
the code/patch.  See,

https://lore.kernel.org/mm-commits/YDAbeDsG7GhV6s6B@carbon.dhcp.thefacebook.com/

This patch is actually in Andrew's tree.
-- 
Mike Kravetz