Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] hugetlbfs: show pagesize in unit of GB if possible
To:     David Rientjes <rientjes@google.com>
CC:     <akpm@linux-foundation.org>, <mike.kravetz@oracle.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
References: <20210130090339.4378-1-linmiaohe@huawei.com>
 <f5ac7d57-6653-aae-f119-b87d72acf192@google.com>
 <24ab70d6-1d23-d118-f1e7-473f01615dcc@huawei.com>
 <c755cad3-1020-46bc-2c4c-7e382ad366f5@google.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <0c9187f0-39c8-8f7d-79a7-9823cba43c5c@huawei.com>
Date:   Tue, 2 Feb 2021 09:26:03 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <c755cad3-1020-46bc-2c4c-7e382ad366f5@google.com>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi:
On 2021/2/2 5:31, David Rientjes wrote:
> On Mon, 1 Feb 2021, Miaohe Lin wrote:
> 
>>>> Hugepage size in unit of GB is supported. We could show pagesize in unit of
>>>> GB to make it more friendly to read. Also rework the calculation code of
>>>> page size unit to make it more readable.
>>>>
>>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>>> ---
>>>>  fs/hugetlbfs/inode.c | 12 ++++++++----
>>>>  1 file changed, 8 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>>>> index 3a08fbae3b53..40a9795f250a 100644
>>>> --- a/fs/hugetlbfs/inode.c
>>>> +++ b/fs/hugetlbfs/inode.c
>>>> @@ -1014,11 +1014,15 @@ static int hugetlbfs_show_options(struct seq_file *m, struct dentry *root)
>>>>  	if (sbinfo->max_inodes != -1)
>>>>  		seq_printf(m, ",nr_inodes=%lu", sbinfo->max_inodes);
>>>>  
>>>> -	hpage_size /= 1024;
>>>> -	mod = 'K';
>>>> -	if (hpage_size >= 1024) {
>>>> -		hpage_size /= 1024;
>>>> +	if (hpage_size >= SZ_1G) {
>>>> +		hpage_size /= SZ_1G;
>>>> +		mod = 'G';
>>>> +	} else if (hpage_size >= SZ_1M) {
>>>> +		hpage_size /= SZ_1M;
>>>>  		mod = 'M';
>>>> +	} else {
>>>> +		hpage_size /= SZ_1K;
>>>> +		mod = 'K';
>>>>  	}
>>>>  	seq_printf(m, ",pagesize=%lu%c", hpage_size, mod);
>>>>  	if (spool) {
>>>
>>> NACK, this can break existing userspace parsing.
>>> .
>>>
>>
>> I see. I should take care of this. Many thanks.
>>
> 
> Thanks.  It's an important point to emphasize because it shows how 
> important user-facing interfaces are.  Once the hugetlbfs mount options 
> are printed in the way they are, it becomes very difficult to change them 
> because there can be userspace in the wild that would break as a result.  
> This is why it's crucial to be very careful when specifying user-facing 
> interfaces the first time so they are extensible.
> .
> 

Many thanks for detailed explanation! I will keep this in mind! Thanks again.