[PATCH] f2fs: refactor f2fs_gc to call checkpoint in urgent condition

[Jaegeuk Kim]

The major change is to call checkpoint, if there's not enough space while having
some prefree segments in FG_GC case.

Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
---
 fs/f2fs/gc.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index c748cdfb0501..0a823d2e8b9d 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1829,7 +1829,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 		goto stop;
 	}
 
-	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) {
+	/* Let's run FG_GC, if we don't have enough space. */
+	if (has_not_enough_free_secs(sbi, 0, 0)) {
+		gc_type = FG_GC;
+
 		/*
 		 * For example, if there are many prefree_segments below given
 		 * threshold, we can make them free by checkpoint. Then, we
@@ -1840,8 +1843,6 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 			if (ret)
 				goto stop;
 		}
-		if (has_not_enough_free_secs(sbi, 0, 0))
-			gc_type = FG_GC;
 	}
 
 	/* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
@@ -1868,19 +1869,14 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 	if (seg_freed == f2fs_usable_segs_in_sec(sbi, segno))
 		sec_freed++;
 
-	if (gc_type == FG_GC)
+	if (gc_type == FG_GC) {
 		sbi->cur_victim_sec = NULL_SEGNO;
 
-	if (gc_control->init_gc_type == FG_GC ||
-	    !has_not_enough_free_secs(sbi,
-				(gc_type == FG_GC) ? sec_freed : 0, 0)) {
-		if (gc_type == FG_GC && sec_freed < gc_control->nr_free_secs)
-			goto go_gc_more;
-		goto stop;
-	}
-
-	/* FG_GC stops GC by skip_count */
-	if (gc_type == FG_GC) {
+		if (!has_not_enough_free_secs(sbi, sec_freed, 0)) {
+			if (sec_freed < gc_control->nr_free_secs)
+				goto go_gc_more;
+			goto stop;
+		}
 		if (sbi->skipped_gc_rwsem)
 			skipped_round++;
 		round++;
@@ -1889,6 +1885,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 			ret = f2fs_write_checkpoint(sbi, &cpc);
 			goto stop;
 		}
+	} else if (!has_not_enough_free_secs(sbi, 0, 0)) {
+		goto stop;
 	}
 
 	__get_secs_required(sbi, NULL, &upper_secs, NULL);
-- 
2.40.0.577.gac1e443424-goog


> 
> Thanks,
> 
> > 
> > 1832
> > 1833         if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) {
> > 1834                 /*
> > 1835                  * For example, if there are many prefree_segments below given
> > 1836                  * threshold, we can make them free by checkpoint. Then, we
> > 1837                  * secure free segments which doesn't need fggc any more.
> > 1838                  */
> > 1839                 if (prefree_segments(sbi)) {
> > 1840                         ret = f2fs_write_checkpoint(sbi, &cpc);
> > 1841                         if (ret)
> > 1842                                 goto stop;
> > 1843                 }
> > 1844                 if (has_not_enough_free_secs(sbi, 0, 0))
> > 1845                         gc_type = FG_GC;
> > 1846         }
> > 
> > > 
> > > One other concern is for those path as below:
> > > - disable_checkpoint
> > > - ioc_gc
> > > - ioc_gc_range
> > > - ioc_resize
> > > ...
> > 
> > I think the upper caller should decide to call checkpoint, if they want to
> > reclaim the prefree likewise f2fs_disable_checkpoint.
> > 
> > > 
> > > We've passed gc_type as FG_GC, but the demand here is to migrate block in time,
> > > rather than dirtying blocks, and callers don't expect checkpoint in f2fs_gc(),
> > > instead the callers will do the checkpoit as it needs.
> > > 
> > > That means it's better to decouple FG_GC and write_checkpoint behavior, so I
> > > added another parameter .reclaim_space to just let f2fs_balance_fs() to trigger
> > > checkpoit in the end of f2fs_gc().
> > 
> > > 
> > > Thanks,
> > > 
> > > > +	} else if (gc_type == FG_GC) {
> > > > +		/* FG_GC stops GC by skip_count */
> > > >    		if (sbi->skipped_gc_rwsem)
> > > >    			skipped_round++;
> > > >    		round++;
> > > >    		if (skipped_round > MAX_SKIP_GC_COUNT &&
> > > > -				skipped_round * 2 >= round) {
> > > > -			ret = f2fs_write_checkpoint(sbi, &cpc);
> > > > -			goto stop;
> > > > -		}
> > > > +				skipped_round * 2 >= round)
> > > > +			stop_gc = true;
> > > >    	}
> > > >    	__get_secs_required(sbi, NULL, &upper_secs, NULL);
> > > > @@ -1901,12 +1898,13 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
> > > >    				prefree_segments(sbi)) {
> > > >    		ret = f2fs_write_checkpoint(sbi, &cpc);
> > > >    		if (ret)
> > > > -			goto stop;
> > > > +			stop_gc = true;
> > > >    	}
> > > >    go_gc_more:
> > > > -	segno = NULL_SEGNO;
> > > > -	goto gc_more;
> > > > -
> > > > +	if (!stop_gc) {
> > > > +		segno = NULL_SEGNO;
> > > > +		goto gc_more;
> > > > +	}
> > > >    stop:
> > > >    	SIT_I(sbi)->last_victim[ALLOC_NEXT] = 0;
> > > >    	SIT_I(sbi)->last_victim[FLUSH_DEVICE] = gc_control->victim_segno;