linux-kernel - Re: [PATCH 5/6] shmem: update documentation

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Date:   Wed, 8 Mar 2023 14:16:02 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     hughd@...gle.com, akpm@...ux-foundation.org, willy@...radead.org,
        brauner@...nel.org, linux-mm@...ck.org, p.raghav@...sung.com,
        da.gomez@...sung.com, a.manzanares@...sung.com, dave@...olabs.net,
        yosryahmed@...gle.com, keescook@...omium.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] shmem: update documentation

On Mon, Mar 06, 2023 at 03:04:57PM +0100, David Hildenbrand wrote:
> On 03.03.23 00:27, Luis Chamberlain wrote:
> > Update the docs to reflect a bit better why some folks prefer tmpfs
> > over ramfs and clarify a bit more about the difference between brd
> > ramdisks.
> > 
> > Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> > ---
> >   Documentation/filesystems/tmpfs.rst | 27 +++++++++++++++++++--------
> >   1 file changed, 19 insertions(+), 8 deletions(-)
> > 
> > diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
> > index 0408c245785e..e77ebdacadd0 100644
> > --- a/Documentation/filesystems/tmpfs.rst
> > +++ b/Documentation/filesystems/tmpfs.rst
> > @@ -13,14 +13,25 @@ everything stored therein is lost.
> >   tmpfs puts everything into the kernel internal caches and grows and
> >   shrinks to accommodate the files it contains and is able to swap
> > -unneeded pages out to swap space. It has maximum size limits which can
> > -be adjusted on the fly via 'mount -o remount ...'
> > -
> > -If you compare it to ramfs (which was the template to create tmpfs)
> > -you gain swapping and limit checking. Another similar thing is the RAM
> > -disk (/dev/ram*), which simulates a fixed size hard disk in physical
> > -RAM, where you have to create an ordinary filesystem on top. Ramdisks
> > -cannot swap and you do not have the possibility to resize them.
> > +unneeded pages out to swap space.
> 
> I suppose, in contrast to ramfs, tmpfs also supports THP. Maybe worth adding
> as well.

Good call, both the mount and the sysfs file (which is registered by
THP) lacks any documentation so I'll just add docs for both.

  Luis