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Re: [PATCH 4/6] xfs: kill the b_strat callback in xfs_buf

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 4/6] xfs: kill the b_strat callback in xfs_buf
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 20 Jul 2010 17:41:29 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20100718203926.427127966@xxxxxxxxxxxxxxxxxxxxxx>
References: <20100718203848.927859114@xxxxxxxxxxxxxxxxxxxxxx> <20100718203926.427127966@xxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Sun, Jul 18, 2010 at 04:38:52PM -0400, Christoph Hellwig wrote:
> The b_strat callback is used by xfs_buf_iostrategy to perform additional
> checks before submitting a buffer.  It is used in xfs_bwrite and when
> writing out delayed buffers.  In xfs_bwrite it we can de-virtualize the
> call easily as b_strat is set a few lines above the call to
> xfs_buf_iostrategy.  For the delayed buffers the rationale is a bit
> more complicated:
> 
>  - there are three callers of xfs_buf_delwri_queue, which places buffers
>    on the delwri list:
>     (1) xfs_bdwrite - this sets up b_strat, so it's fine
>     (2) xfs_buf_iorequest.  None of the callers can have XBF_DELWRI set:
>       - xlog_bdstrat is only used for log buffers, which are never delwri
>       - _xfs_buf_read explicitly clears the delwri flag
>       - xfs_buf_iodone_work retries log buffers only
>       - xfsbdstrat - only used for reads, superblock writes without the
>         delwri flag, log I/O and file zeroing with explicitly allocated
>         buffers.
>       - xfs_buf_iostrategy - only calls xfs_buf_iorequest if b_strat is
>         not set
>     (3) xfs_buf_unlock
>       - only puts the buffer on the delwri list if the DELWRI flag is
>         already set.  The DELWRI flag is only ever set in xfs_bwrite,
>         xfs_buf_iodone_callbacks, or xfs_trans_log_buf.  For
>         xfs_buf_iodone_callbacks and xfs_trans_log_buf we require
>         an initialized buf item, which means b_strat was set to
>         xfs_bdstrat_cb in xfs_buf_item_init.
> 
> Conclusion: we can just get rid of the callback and replace it with
> explicit calls to xfs_bdstrat_cb.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

looks good.

Reviewed-by: Dave Chinner <david@xxxxxxxxxxxxx>

-- 
Dave Chinner
david@xxxxxxxxxxxxx

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