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Date:   Tue, 2 Feb 2021 09:26:03 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     David Rientjes <rientjes@...gle.com>
CC:     <akpm@...ux-foundation.org>, <mike.kravetz@...cle.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hugetlbfs: show pagesize in unit of GB if possible

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@...wei.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.

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