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 01:28:10 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     Christoph Hellwig <hch@...radead.org>, 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 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.