Re: [RFC PATCH] fs: introduce ST_HUGE flag and set it to tmpfs and hugetlbfs

From: Yang Shi
Date: Thu Apr 19 2018 - 20:18:48 EST

On 4/19/18 1:28 AM, Christoph Hellwig wrote:
On Wed, Apr 18, 2018 at 11:18:25AM -0700, Yang Shi wrote:
Yes, thanks for the suggestion. I did think about it before I went with the
new flag. Not like hugetlb, THP will *not* guarantee huge page is used all
the time, it may fallback to regular 4K page or may get split. I'm not sure
how the applications use f_bsize field, it might break existing applications
and the value might be abused by applications to have counter optimization.
So, IMHO, a new flag may sound safer.
But st_blksize isn't the block size, that is why I suggested it. It is
the preferred I/O size, and various file systems can report way
larger values than the block size already.

Thanks. If it is safe to applications, It definitely can return huge page size via st_blksize.

Is it safe to return huge page size via statfs->f_bsize? It sounds it has not to be the physical block size too. The man page says it is "Optimal transfer block size".