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

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Date:   Thu, 19 Apr 2018 17:18:20 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     viro@...iv.linux.org.uk, nyc@...omorphy.com,
        mike.kravetz@...cle.com, kirill.shutemov@...ux.intel.com,
        hughd@...gle.com, akpm@...ux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] fs: introduce ST_HUGE flag and set it to tmpfs and
 hugetlbfs



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".

Yang