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

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Message-ID: <20161219212413.GN4326@dastard>
Date:   Tue, 20 Dec 2016 08:24:13 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     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 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.

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