linux-kernel - Re: [PATCHv2 1/1] ext4: don't put symlink in pagecache into highmem

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Message-ID: <20180206231149.GC1977@thunk.org>
Date:   Tue, 6 Feb 2018 18:11:49 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Jin Qian <jinqian@...roid.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jin Qian <jinqian@...gle.com>,
        stable@...r.kernel.org
Subject: Re: [PATCHv2 1/1] ext4: don't put symlink in pagecache into highmem

On Tue, Feb 06, 2018 at 12:39:53PM -0800, Greg KH wrote:
> On Tue, Feb 06, 2018 at 11:09:37AM -0800, Jin Qian wrote:
> > From: Jin Qian <jinqian@...gle.com>
> > 
> > partial backport from 21fc61c73c3903c4c312d0802da01ec2b323d174 upstream
> > to v4.4 to prevent virt_to_page on highmem.
>
> Ted, any objection to this patch?

No objections with my ext4 hat on.

It should be noted though that this is a partial backport because it
only fixes ext4, while Al's original upstream fix addressed a much
larger set of file systems.  In the Android kernel the f2fs fix had
been backported separately.  But for the upstream kernel, it *might*
be the case that we should try backporting the original commit so that
in case there is some other general purpose distribution decides (a)
to base their system on 4.4, and (b) support a 32-bit kernel, they get
the more general bug fixes which applies for btrfs, isofs, ocfs2, nfs,
etc.

I haevn't been paying attention to what LTS kernels general purpose
distro's are using, so I don't know how important this would be.  And
if there are companies like Cloudflare which are using upstream LTS
kernel, it seems unlikely they would want to use a 32-bit kernel,
so.... shrug.  Greg, I'll let you decide if you want to backport the
full commit or not.

(We had a similar discussion on the AOSP kernel, and came to the
conclusion that we only needed to make the patch support ext4.  No one
was going to test the other file systems besides ext4 and f2fs,
anyway.  But the calculus might be different might be different for
the general upstream LTS kernel.)

				- Ted