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

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Message-ID: <20180419090512.apnalks6s5z63lqq@node.shutemov.name>
Date:   Thu, 19 Apr 2018 12:05:12 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, 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 Thu, Apr 19, 2018 at 01:28:10AM -0700, 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.

I agree. This looks like a better fit.

-- 
 Kirill A. Shutemov