Re: [PATCH 5/5] hugetlbfs: fix confusing hugetlbfs stat

Mike Kravetz
2022-07-22T22:55:57Z

On 07/22/22 14:38, Miaohe Lin wrote:
> 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.

Thanks for the additional information (and test program)!

From the hugetlbfs documentation:
"If the ``size``, ``min_size`` or ``nr_inodes`` option is not provided on
command line then no limits are set."

So, having those values set to -1 indicates there is no limit set.

With this change, 0 is reported for the case where there is no limit set as
well as the case where the max value is 0.

There may be some value in reporting -1 as is done today.

To be honest, I am not sure what is the correct behavior here. Unless
there is a user visible issue/problem, I am hesitant to change. Other
opinions are welcome.
--
Mike Kravetz

>
> 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@localhost ~]# mount -t hugetlbfs none /root/huge/
> [root@localhost ~]# ./stat
> f_blocks 0, f_bavail 0, f_bfree 0, f_files 0, f_ffree 0
> [root@localhost ~]# umount /root/huge/
> [root@localhost ~]# mount -t hugetlbfs -o min_size=32M none /root/huge/
> [root@localhost ~]# ./stat
> f_blocks -1, f_bavail -1, f_bfree -1, f_files -1, f_ffree -1
> [root@localhost ~]# umount /root/huge/
> [root@localhost ~]# mount -t hugetlbfs -o min_size=32M,size=64M none /root/huge/
> [root@localhost ~]# ./stat
> f_blocks 32, f_bavail 32, f_bfree 32, f_files -1, f_ffree -1
> [root@localhost ~]# umount /root/huge/
> [root@localhost ~]# mount -t hugetlbfs -o min_size=32M,size=64M,nr_inodes=1024 none /root/huge/
> [root@localhost ~]# ./stat
> f_blocks 32, f_bavail 32, f_bfree 32, f_files 1024, f_ffree 1023
> [root@localhost ~]# umount /root/huge/
>
> Or am I miss something?
>
> >
>
> Thanks.