linux-kernel - Re: [RFC PATCH 0/3] restructure memfd code

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Date:   Tue, 21 Nov 2017 09:32:15 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Marc-André Lureau 
        <marcandre.lureau@...hat.com>,
        David Herrmann <dh.herrmann@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 0/3] restructure memfd code

On Wed, 2017-11-08 at 17:41 -0800, Mike Kravetz wrote:
> With the addition of memfd hugetlbfs support, we now have the
> situation
> where memfd depends on TMPFS -or- HUGETLBFS.  Previously, memfd was
> only
> supported on tmpfs, so it made sense that the code resides in
> shmem.c.
> 
> This patch series moves the memfd code to separate files (memfd.c and
> memfd.h).  It creates a new config option MEMFD_CREATE that is
> defined
> if either TMPFS or HUGETLBFS is defined.
> 
> In the current code, memfd is only functional if TMPFS is
> defined.  If
> HUGETLFS is defined and TMPFS is not defined, then memfd
> functionality
> will not be available for hugetlbfs.  This does not cause BUGs, just
> a
> potential lack of desired functionality.
> 
> Another way to approach this issue would be to simply make HUGETLBFS
> depend on TMPFS.
> 
> This patch series is built on top of the Marc-André Lureau v3 series
> "memfd: add sealing to hugetlb-backed memory":
> http://lkml.kernel.org/r/20171107122800.25517-1-marcandre.lureau@redh
> at.com
> 
> Mike Kravetz (3):
>   mm: hugetlbfs: move HUGETLBFS_I outside #ifdef CONFIG_HUGETLBFS
>   mm: memfd: split out memfd for use by multiple filesystems
>   mm: memfd: remove memfd code from shmem files and use new memfd
> files
> 

Hi Mike,

This looks like a useful change. After applying patch 2, you end up
with duplicate definitions of number of symbols though. Although those
duplicates will not cause compilation problems since memfd.c is not
compiled until after patch 3 has been applied, would it make more sense
to combine moving of all code in one patch?

--
Khalid