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

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Message-ID: <8d090981-629c-95fb-fe45-fe26b3c2165f@oracle.com>
Date:   Tue, 21 Nov 2017 16:40:15 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Khalid Aziz <khalid.aziz@...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 11/21/2017 08:32 AM, Khalid Aziz wrote:
> 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?

Thanks Khalid,

I was aware of this situation when creating the patch.  It was broken out
as above simply to make it easier to review/understand.  Not sure if that
is actually the case.  The other option was as you suggested to simply
combine the add/remove as a single patch.

I am somewhat waiting to see how Marc-André Lureau's file sealing series
progresses as this series touches the same code.
-- 
Mike Kravetz