Commit 83bac569 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Carlos Maiolino
Browse files

xfs: prevent gc from picking the same zone twice 



When we are picking a zone for gc it might already be in the pipeline
which can lead to us moving the same data twice resulting in in write
amplification and a very unfortunate case where we keep on garbage
collecting the zone we just filled with migrated data stopping all
forward progress.

Fix this by introducing a count of on-going GC operations on a zone, and
skip any zone with ongoing GC when picking a new victim.

Fixes: 080d01c4 ("xfs: implement zoned garbage collection")
Signed-off-by: default avatarHans Holmberg <hans.holmberg@wdc.com>
Co-developed-by: default avatarHans Holmberg <hans.holmberg@wdc.com>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDamien Le Moal <dlemoal@kernel.org>
Reviewed-by: default avatarCarlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <djwong@kernel.org>
Tested-by: default avatarDamien Le Moal <dlemoal@kernel.org>
Signed-off-by: default avatarCarlos Maiolino <cem@kernel.org>
parent f477af0c

fs/xfs/libxfs/xfs_rtgroup.h

+6 −0
Original line number Diff line number Diff line
@@ -50,6 +50,12 @@ struct xfs_rtgroup { 
		uint8_t			*rtg_rsum_cache;

		struct xfs_open_zone	*rtg_open_zone;

	};



	/*

	 * Count of outstanding GC operations for zoned XFS.  Any RTG with a

	 * non-zero rtg_gccount will not be picked as new GC victim.

	 */

	atomic_t		rtg_gccount;

};



/*

fs/xfs/xfs_zone_gc.c

+27 −0
Original line number Diff line number Diff line
@@ -114,6 +114,8 @@ struct xfs_gc_bio { 
	/* Open Zone being written to */

	struct xfs_open_zone		*oz;



	struct xfs_rtgroup		*victim_rtg;



	/* Bio used for reads and writes, including the bvec used by it */

	struct bio_vec			bv;

	struct bio			bio;	/* must be last */
@@ -264,6 +266,7 @@ xfs_zone_gc_iter_init( 
	iter->rec_count = 0;

	iter->rec_idx = 0;

	iter->victim_rtg = victim_rtg;

	atomic_inc(&victim_rtg->rtg_gccount);

}



/*
@@ -362,6 +365,7 @@ xfs_zone_gc_query( 


	return 0;

done:

	atomic_dec(&iter->victim_rtg->rtg_gccount);

	xfs_rtgroup_rele(iter->victim_rtg);

	iter->victim_rtg = NULL;

	return 0;
@@ -451,6 +455,20 @@ xfs_zone_gc_pick_victim_from( 
		if (!rtg)

			continue;



		/*

		 * If the zone is already undergoing GC, don't pick it again.

		 *

		 * This prevents us from picking one of the zones for which we

		 * already submitted GC I/O, but for which the remapping hasn't

		 * concluded yet.  This won't cause data corruption, but

		 * increases write amplification and slows down GC, so this is

		 * a bad thing.

		 */

		if (atomic_read(&rtg->rtg_gccount)) {

			xfs_rtgroup_rele(rtg);

			continue;

		}



		/* skip zones that are just waiting for a reset */

		if (rtg_rmap(rtg)->i_used_blocks == 0 ||

		    rtg_rmap(rtg)->i_used_blocks >= victim_used) {
@@ -688,6 +706,9 @@ xfs_zone_gc_start_chunk( 
	chunk->scratch = &data->scratch[data->scratch_idx];

	chunk->data = data;

	chunk->oz = oz;

	chunk->victim_rtg = iter->victim_rtg;

	atomic_inc(&chunk->victim_rtg->rtg_group.xg_active_ref);

	atomic_inc(&chunk->victim_rtg->rtg_gccount);



	bio->bi_iter.bi_sector = xfs_rtb_to_daddr(mp, chunk->old_startblock);

	bio->bi_end_io = xfs_zone_gc_end_io;
@@ -710,6 +731,8 @@ static void 
xfs_zone_gc_free_chunk(

	struct xfs_gc_bio	*chunk)

{

	atomic_dec(&chunk->victim_rtg->rtg_gccount);

	xfs_rtgroup_rele(chunk->victim_rtg);

	list_del(&chunk->entry);

	xfs_open_zone_put(chunk->oz);

	xfs_irele(chunk->ip);
@@ -770,6 +793,10 @@ xfs_zone_gc_split_write( 
	split_chunk->oz = chunk->oz;

	atomic_inc(&chunk->oz->oz_ref);



	split_chunk->victim_rtg = chunk->victim_rtg;

	atomic_inc(&chunk->victim_rtg->rtg_group.xg_active_ref);

	atomic_inc(&chunk->victim_rtg->rtg_gccount);



	chunk->offset += split_len;

	chunk->len -= split_len;

	chunk->old_startblock += XFS_B_TO_FSB(data->mp, split_len);