Re: [PATCH 2/3] xfs: only invalidate blocks if we're going to free them

[Brian Foster <bfoster@redhat.com>]

On Wed, Oct 09, 2019 at 09:48:47AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> When we're discarding old btree blocks after a repair, only invalidate
> the buffers for the ones that we're freeing -- if the metadata was
> crosslinked with another data structure, we don't want to touch it.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/scrub/repair.c |   76 +++++++++++++++++++++++--------------------------
>  fs/xfs/scrub/repair.h |    1 -
>  2 files changed, 35 insertions(+), 42 deletions(-)
> 
> 
> diff --git a/fs/xfs/scrub/repair.c b/fs/xfs/scrub/repair.c
> index 3a58788e0bd8..e21faef6db5a 100644
> --- a/fs/xfs/scrub/repair.c
> +++ b/fs/xfs/scrub/repair.c
...
> @@ -515,6 +477,35 @@ xrep_put_freelist(
>  	return 0;
>  }
>  
> +/* Try to invalidate the incore buffer for a block that we're about to free. */
> +STATIC void
> +xrep_reap_invalidate_block(
> +	struct xfs_scrub	*sc,
> +	xfs_fsblock_t		fsbno)
> +{
> +	struct xfs_buf		*bp;
> +
> +	/*
> +	 * For each block in each extent, see if there's an incore buffer for
> +	 * exactly that block; if so, invalidate it.  The buffer cache only
> +	 * lets us look for one buffer at a time, so we have to look one block
> +	 * at a time.  Avoid invalidating AG headers and post-EOFS blocks
> +	 * because we never own those; and if we can't TRYLOCK the buffer we
> +	 * assume it's owned by someone else.
> +	 */
> +	/* Skip AG headers and post-EOFS blocks */

The comment doesn't seem to quite go with the implementation any longer.
Also, there's probably no need to have two separate comments here.
Otherwise looks Ok.

Brian

> +	if (!xfs_verify_fsbno(sc->mp, fsbno))
> +		return;
> +	bp = xfs_buf_incore(sc->mp->m_ddev_targp,
> +			XFS_FSB_TO_DADDR(sc->mp, fsbno),
> +			XFS_FSB_TO_BB(sc->mp, 1), XBF_TRYLOCK);
> +	if (!bp)
> +		return;
> +
> +	xfs_trans_bjoin(sc->tp, bp);
> +	xfs_trans_binval(sc->tp, bp);
> +}
> +
>  /* Dispose of a single block. */
>  STATIC int
>  xrep_reap_block(
> @@ -568,12 +559,15 @@ xrep_reap_block(
>  	 * blow on writeout, the filesystem will shut down, and the admin gets
>  	 * to run xfs_repair.
>  	 */
> -	if (has_other_rmap)
> +	if (has_other_rmap) {
>  		error = xfs_rmap_free(sc->tp, agf_bp, agno, agbno, 1, oinfo);
> -	else if (resv == XFS_AG_RESV_AGFL)
> +	} else if (resv == XFS_AG_RESV_AGFL) {
> +		xrep_reap_invalidate_block(sc, fsbno);
>  		error = xrep_put_freelist(sc, agbno);
> -	else
> +	} else {
> +		xrep_reap_invalidate_block(sc, fsbno);
>  		error = xfs_free_extent(sc->tp, fsbno, 1, oinfo, resv);
> +	}
>  	if (agf_bp != sc->sa.agf_bp)
>  		xfs_trans_brelse(sc->tp, agf_bp);
>  	if (error)
> diff --git a/fs/xfs/scrub/repair.h b/fs/xfs/scrub/repair.h
> index 60c61d7052a8..eab41928990f 100644
> --- a/fs/xfs/scrub/repair.h
> +++ b/fs/xfs/scrub/repair.h
> @@ -31,7 +31,6 @@ int xrep_init_btblock(struct xfs_scrub *sc, xfs_fsblock_t fsb,
>  struct xfs_bitmap;
>  
>  int xrep_fix_freelist(struct xfs_scrub *sc, bool can_shrink);
> -int xrep_invalidate_blocks(struct xfs_scrub *sc, struct xfs_bitmap *btlist);
>  int xrep_reap_extents(struct xfs_scrub *sc, struct xfs_bitmap *exlist,
>  		const struct xfs_owner_info *oinfo, enum xfs_ag_resv_type type);
>  
>