linux-ext4 - Re: [PATCH 2/9] xfs: introduce and use KM_NOLOCKDEP to silence reclaim lockdep false positives

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Message-ID: <20161219220619.GA7296@birch.djwong.org>
Date:   Mon, 19 Dec 2016 14:06:19 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Theodore Ts'o" <tytso@....edu>, Chris Mason <clm@...com>,
        David Sterba <dsterba@...e.cz>, Jan Kara <jack@...e.cz>,
        ceph-devel@...r.kernel.org, cluster-devel@...hat.com,
        linux-nfs@...r.kernel.org, logfs@...fs.org,
        linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-mtd@...ts.infradead.org,
        reiserfs-devel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 2/9] xfs: introduce and use KM_NOLOCKDEP to silence
 reclaim lockdep false positives

On Tue, Dec 20, 2016 at 08:24:13AM +1100, Dave Chinner wrote:
> On Thu, Dec 15, 2016 at 03:07:08PM +0100, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > Now that the page allocator offers __GFP_NOLOCKDEP let's introduce
> > KM_NOLOCKDEP alias for the xfs allocation APIs. While we are at it
> > also change KM_NOFS users introduced by b17cb364dbbb ("xfs: fix missing
> > KM_NOFS tags to keep lockdep happy") and use the new flag for them
> > instead. There is really no reason to make these allocations contexts
> > weaker just because of the lockdep which even might not be enabled
> > in most cases.
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> 
> I'd suggest that it might be better to drop this patch for now -
> it's not necessary for the context flag changeover but does
> introduce a risk of regressions if the conversion is wrong.

I was just about to write in that while I didn't see anything obviously
wrong with the NOFS removals, I also don't know for sure that we can't
end up recursively in those code paths (specifically the directory
traversal thing).

--D

> Hence I think this is better as a completely separate series
> which audits and changes all the unnecessary KM_NOFS allocations
> in one go. I've never liked whack-a-mole style changes like this -
> do it once, do it properly....
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com
> --
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