Re: [PATCH] xfs: Correctly invert xfs_buftarg LRU isolation logic

[Darrick J. Wong]

On Mon, Mar 05, 2018 at 11:19:46AM +0100, Vratislav Bendel wrote:
> (In response to Luis' comment:)
> > Can you add a respective Fixes: tag?
> 
> It was apparently present since LRU was added to xfs buffer cache via:
> commit 430cbeb86fdcbbdabea7d4aa65307de8de425350
> [xfs: add a lru to the XFS buffer cache]
> 
> But I wouldn't say this patch "fixes" that commit.
> What do you think? Should a fixes tag be added in this case?
> 
> 
> > Also what effects are observed by
> > the user when this happens on the kernel log?
> 
> I haven't spotted any differences visible to user, nor in the kernel log.
> 
> (In response to Brian's comment:)
> >> However, as per documentation, atomic_add_unless() returns _zero_
> >> if the atomic value was originally equal to the specified *unsless* value.
> >>
> > Nit:                                                         unless
> 
> Thanks very much for feedback. Since it's my very first upstream
> commit-proposal,
> I expected that some polish would be needed.
> 
> 
> > It might be worth pointing out in the commit log that currently isolated
> > buffers end up right back on the LRU once they are released, because
> > ->b_lru_ref remains elevated. Therefore, this patch essentially fixes
> > that circuitous route by leaving them on the LRU as originally intended.
> > Otherwise this looks Ok to me:
> 
> So the final commit message could be:
> ~~~
> Currently the xfs_buftarg_isolate() is causing an xfs_buffer

"Due to an inverted logic mistake in xfs_buftarg_isolate()..."?

> with zero b_lru_ref, to take another trip around LRU, while

                   ^^^^ no need for this comma

> isolating buffers with non-zero b_lru_ref.
> 
> Additionally those isolated buffers end up right back on the LRU
> once they are released, because ->b_lru_ref remains elevated.
> 
> Fix that circuitous route by leaving them on the LRU
> as originally intended.

Otherwise this seems fine to me; can you please resend the patch w/
updated change log and reviewed-by tags?

Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>

--D

> 
> >> Signed-off-by: Vratislav Bendel <vbendel@xxxxxxxxxx>
> > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> > ---
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