linux-kernel - Re: [PATCH 5/5] hugetlbfs: fix confusing hugetlbfs stat

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Date:   Fri, 22 Jul 2022 14:38:10 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
CC:     <akpm@...ux-foundation.org>, <songmuchun@...edance.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] hugetlbfs: fix confusing hugetlbfs stat

On 2022/7/22 8:28, Mike Kravetz wrote:
> On 07/21/22 21:16, Miaohe Lin wrote:
>> When size option is not specified, f_blocks, f_bavail and f_bfree will be
>> set to -1 instead of 0. Likewise, when nr_inodes is not specified, f_files
>> and f_ffree will be set to -1 too. Check max_hpages and max_inodes against
>> -1 first to make sure 0 is reported for max/free/used when no limit is set
>> as the comment states.
> 
> Just curious, where are you seeing values reported as -1?  The check

>From the standard statvfs() function.

> for sbinfo->spool was supposed to handle these cases.  Seems like it

sbinfo->spool could be created when ctx->max_hpages == -1 while
ctx->min_hpages != -1 in hugetlbfs_fill_super.

> should handle the max_hpages == -1 case.  But, it doesn't look like it
> considers the max_inodes == -1 case.
> 
> If I create/mount a hugetlb filesystem without specifying size or nr_inodes,
> df seems to report zero instead of -1.
> 
> Just want to understand the reasoning behind the change.

I wrote a test program:

#include <sys/statvfs.h>
#include <stdio.h>

int main(void)
{
	struct statvfs buf;

	if (statvfs("/root/huge/", &buf) == -1) {
 		printf("statvfs() error\n");
		return -1;
	}
	printf("f_blocks %lld, f_bavail %lld, f_bfree %lld, f_files %lld, f_ffree %lld\n",
		buf.f_blocks, buf.f_bavail, buf.f_bfree, buf.f_files, buf.f_ffree);
	return 0;
}

And test it in my env:
[root@...alhost ~]# mount -t hugetlbfs none /root/huge/
[root@...alhost ~]# ./stat
f_blocks 0, f_bavail 0, f_bfree 0, f_files 0, f_ffree 0
[root@...alhost ~]# umount /root/huge/
[root@...alhost ~]# mount -t hugetlbfs -o min_size=32M none /root/huge/
[root@...alhost ~]# ./stat
f_blocks -1, f_bavail -1, f_bfree -1, f_files -1, f_ffree -1
[root@...alhost ~]# umount /root/huge/
[root@...alhost ~]# mount -t hugetlbfs -o min_size=32M,size=64M none /root/huge/
[root@...alhost ~]# ./stat
f_blocks 32, f_bavail 32, f_bfree 32, f_files -1, f_ffree -1
[root@...alhost ~]# umount /root/huge/
[root@...alhost ~]# mount -t hugetlbfs -o min_size=32M,size=64M,nr_inodes=1024 none /root/huge/
[root@...alhost ~]# ./stat
f_blocks 32, f_bavail 32, f_bfree 32, f_files 1024, f_ffree 1023
[root@...alhost ~]# umount /root/huge/

Or am I miss something?

> 

Thanks.