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Date:   Thu, 12 May 2022 13:50:19 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [PATCH 4/5 v2] f2fs: do not stop GC when requiring a free section
Message-ID: <Yn1zC6MUZOEbSlWK@google.com>
References: <20220506232032.1264078-1-jaegeuk@kernel.org>
 <20220506232032.1264078-4-jaegeuk@kernel.org>
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The f2fs_gc uses a bitmap to indicate pinned sections, but when disabling
chckpoint, we call f2fs_gc() with NULL_SEGNO which selects the same dirty
segment as a victim all the time, resulting in checkpoint=disable failure,
for example. Let's pick another one, if we fail to collect it.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---

 Change log from v1:
  - refactor the code path to avoid ambiguous condition like BG_GC/sec_freed

 fs/f2fs/f2fs.h              |  1 +
 fs/f2fs/file.c              | 12 ++++++++----
 fs/f2fs/gc.c                | 14 +++++++++-----
 fs/f2fs/segment.c           |  3 ++-
 fs/f2fs/super.c             |  3 ++-
 include/trace/events/f2fs.h | 11 ++++++++---
 6 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9920b2d6af8f..492af5b96de1 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1271,6 +1271,7 @@ struct f2fs_gc_control {
 	bool no_bg_gc;			/* check the space and stop bg_gc */
 	bool should_migrate_blocks;	/* should migrate blocks */
 	bool err_gc_skipped;		/* return EAGAIN if GC skipped */
+	unsigned int nr_free_secs;	/* # of free sections to do GC */
 };
 
 /* For s_flag in struct f2fs_sb_info */
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index d0547bef0851..216081ea8c81 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1650,7 +1650,8 @@ static int expand_inode_data(struct inode *inode, loff_t offset,
 	struct f2fs_gc_control gc_control = { .victim_segno = NULL_SEGNO,
 			.init_gc_type = FG_GC,
 			.should_migrate_blocks = false,
-			.err_gc_skipped = true };
+			.err_gc_skipped = true,
+			.nr_free_secs = 0 };
 	pgoff_t pg_start, pg_end;
 	loff_t new_size = i_size_read(inode);
 	loff_t off_end;
@@ -2350,7 +2351,8 @@ static int f2fs_ioc_gc(struct file *filp, unsigned long arg)
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct f2fs_gc_control gc_control = { .victim_segno = NULL_SEGNO,
 			.no_bg_gc = false,
-			.should_migrate_blocks = false };
+			.should_migrate_blocks = false,
+			.nr_free_secs = 0 };
 	__u32 sync;
 	int ret;
 
@@ -2391,7 +2393,8 @@ static int __f2fs_ioc_gc_range(struct file *filp, struct f2fs_gc_range *range)
 			.init_gc_type = range->sync ? FG_GC : BG_GC,
 			.no_bg_gc = false,
 			.should_migrate_blocks = false,
-			.err_gc_skipped = range->sync };
+			.err_gc_skipped = range->sync,
+			.nr_free_secs = 0 };
 	u64 end;
 	int ret;
 
@@ -2837,7 +2840,8 @@ static int f2fs_ioc_flush_device(struct file *filp, unsigned long arg)
 	struct f2fs_gc_control gc_control = {
 			.init_gc_type = FG_GC,
 			.should_migrate_blocks = true,
-			.err_gc_skipped = true };
+			.err_gc_skipped = true,
+			.nr_free_secs = 0 };
 	int ret;
 
 	if (!capable(CAP_SYS_ADMIN))
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index e275b72bc65f..10b24b0f13a5 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -147,6 +147,7 @@ static int gc_thread_func(void *data)
 
 		gc_control.init_gc_type = sync_mode ? FG_GC : BG_GC;
 		gc_control.no_bg_gc = foreground;
+		gc_control.nr_free_secs = foreground ? 1 : 0;
 
 		/* if return value is not zero, no victim was selected */
 		if (f2fs_gc(sbi, &gc_control))
@@ -1761,6 +1762,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 	unsigned int skipped_round = 0, round = 0;
 
 	trace_f2fs_gc_begin(sbi->sb, gc_type, gc_control->no_bg_gc,
+				gc_control->nr_free_secs,
 				get_pages(sbi, F2FS_DIRTY_NODES),
 				get_pages(sbi, F2FS_DIRTY_DENTS),
 				get_pages(sbi, F2FS_DIRTY_IMETA),
@@ -1823,12 +1825,13 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 	if (gc_type == FG_GC)
 		sbi->cur_victim_sec = NULL_SEGNO;
 
-	if (gc_control->init_gc_type == FG_GC)
-		goto stop;
-
-	if (!has_not_enough_free_secs(sbi,
-			(gc_type == FG_GC) ? sec_freed : 0, 0))
+	if (gc_control->init_gc_type == FG_GC ||
+	    !has_not_enough_free_secs(sbi,
+				(gc_type == FG_GC) ? sec_freed : 0, 0)) {
+		if (gc_mode == 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) {
@@ -1849,6 +1852,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
 		if (ret)
 			goto stop;
 	}
+go_gc_more:
 	segno = NULL_SEGNO;
 	goto gc_more;
 
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 8b4f2b1d2cca..0a4180f64291 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -404,7 +404,8 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
 				.init_gc_type = BG_GC,
 				.no_bg_gc = true,
 				.should_migrate_blocks = false,
-				.err_gc_skipped = false };
+				.err_gc_skipped = false,
+				.nr_free_secs = 1 };
 			f2fs_down_write(&sbi->gc_lock);
 			f2fs_gc(sbi, &gc_control);
 		}
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index a28c27eed6d0..63daae67a9d9 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2080,7 +2080,8 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
 			.victim_segno = NULL_SEGNO,
 			.init_gc_type = FG_GC,
 			.should_migrate_blocks = false,
-			.err_gc_skipped = true };
+			.err_gc_skipped = true,
+			.nr_free_secs = 1 };
 
 		f2fs_down_write(&sbi->gc_lock);
 		err = f2fs_gc(sbi, &gc_control);
diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
index 54ec9e543f09..16c67ede85b6 100644
--- a/include/trace/events/f2fs.h
+++ b/include/trace/events/f2fs.h
@@ -645,18 +645,21 @@ TRACE_EVENT(f2fs_background_gc,
 TRACE_EVENT(f2fs_gc_begin,
 
 	TP_PROTO(struct super_block *sb, int gc_type, bool no_bg_gc,
+			unsigned int nr_free_secs,
 			long long dirty_nodes, long long dirty_dents,
 			long long dirty_imeta, unsigned int free_sec,
 			unsigned int free_seg, int reserved_seg,
 			unsigned int prefree_seg),
 
-	TP_ARGS(sb, gc_type, no_bg_gc, dirty_nodes, dirty_dents, dirty_imeta,
+	TP_ARGS(sb, gc_type, no_bg_gc, nr_free_secs, dirty_nodes,
+		dirty_dents, dirty_imeta,
 		free_sec, free_seg, reserved_seg, prefree_seg),
 
 	TP_STRUCT__entry(
 		__field(dev_t,		dev)
 		__field(int,		gc_type)
 		__field(bool,		no_bg_gc)
+		__field(unsigned int,	nr_free_secs)
 		__field(long long,	dirty_nodes)
 		__field(long long,	dirty_dents)
 		__field(long long,	dirty_imeta)
@@ -670,6 +673,7 @@ TRACE_EVENT(f2fs_gc_begin,
 		__entry->dev		= sb->s_dev;
 		__entry->gc_type	= gc_type;
 		__entry->no_bg_gc	= no_bg_gc;
+		__entry->nr_free_secs	= nr_free_secs;
 		__entry->dirty_nodes	= dirty_nodes;
 		__entry->dirty_dents	= dirty_dents;
 		__entry->dirty_imeta	= dirty_imeta;
@@ -679,12 +683,13 @@ TRACE_EVENT(f2fs_gc_begin,
 		__entry->prefree_seg	= prefree_seg;
 	),
 
-	TP_printk("dev = (%d,%d), gc_type = %s, no_background_GC = %d, nodes = %lld, "
-		"dents = %lld, imeta = %lld, free_sec:%u, free_seg:%u, "
+	TP_printk("dev = (%d,%d), gc_type = %s, no_background_GC = %d, nr_free_secs = %u, "
+		"nodes = %lld, dents = %lld, imeta = %lld, free_sec:%u, free_seg:%u, "
 		"rsv_seg:%d, prefree_seg:%u",
 		show_dev(__entry->dev),
 		show_gc_type(__entry->gc_type),
 		(__entry->gc_type == BG_GC) ? __entry->no_bg_gc : -1,
+		__entry->nr_free_secs,
 		__entry->dirty_nodes,
 		__entry->dirty_dents,
 		__entry->dirty_imeta,
-- 
2.36.0.550.gb090851708-goog