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f2fs: fix deadloop in foreground GC

PATCH Superseded Chao Yu 2 participants 3 messages Apr 30, 2022 – May 4, 2022

Subsystems (2)
Stable branch F2FS file system

v1 of 3 Superseded Latest is v3 →

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Chao Yu

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#0 lore raw

PATCH 1/1 f2fs: fix deadloop in foreground GC

As Yanming reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=215914

The root cause is: in a very small sized image, it's very easy to exceed threshold of foreground GC, if we calculate free space and dirty data based on section granularity, in corner case, has_not_enough_free_secs() will always return true, result in deadloop in f2fs_gc().

So this patch refactors has_not_enough_free_secs() as below to fix this issue:
1. calculate needed space based on block granularity, and separate all blocks to two parts, section part, and block part, comparing section part to free section, and comparing block part to free space in openned log.
2. account F2FS_DIRTY_NODES, F2FS_DIRTY_IMETA and F2FS_DIRTY_DENTS as node block consumer;
3. account F2FS_DIRTY_DENTS as data block consumer;

Cc [email protected]
Reported-by Ming Yan <[email protected]>
Signed-off-by Chao Yu <[email protected]>
---
 fs/f2fs/segment.h | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)
fs/f2fs/segment.h +17 -13
index 8a591455d796..28f7aa9b40bf 100644
@@ -575,11 +575,10 @@ static inline int reserved_sections(struct f2fs_sb_info *sbi)
 	return GET_SEC_FROM_SEG(sbi, reserved_segments(sbi));
 }
 
-static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi)
+static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi,
+			unsigned int node_blocks, unsigned int dent_blocks)
 {
-	unsigned int node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
-					get_pages(sbi, F2FS_DIRTY_DENTS);
-	unsigned int dent_blocks = get_pages(sbi, F2FS_DIRTY_DENTS);
+
 	unsigned int segno, left_blocks;
 	int i;
 

@@ -605,19 +604,24 @@ static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi)
 static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
 					int freed, int needed)
 {
-	int node_secs = get_blocktype_secs(sbi, F2FS_DIRTY_NODES);
-	int dent_secs = get_blocktype_secs(sbi, F2FS_DIRTY_DENTS);
-	int imeta_secs = get_blocktype_secs(sbi, F2FS_DIRTY_IMETA);
+	unsigned int total_node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
+					get_pages(sbi, F2FS_DIRTY_DENTS) +
+					get_pages(sbi, F2FS_DIRTY_IMETA);
+	unsigned int total_dent_blocks = get_pages(sbi, F2FS_DIRTY_DENTS);
+	unsigned int node_secs = total_node_blocks / BLKS_PER_SEC(sbi);
+	unsigned int dent_secs = total_dent_blocks / BLKS_PER_SEC(sbi);
+	unsigned int node_blocks = total_node_blocks % BLKS_PER_SEC(sbi);
+	unsigned int dent_blocks = total_dent_blocks % BLKS_PER_SEC(sbi);
 
 	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
 		return false;
 
-	if (free_sections(sbi) + freed == reserved_sections(sbi) + needed &&
-			has_curseg_enough_space(sbi))
-		return false;
-	return (free_sections(sbi) + freed) <=
-		(node_secs + 2 * dent_secs + imeta_secs +
-		reserved_sections(sbi) + needed);
+	if (free_sections(sbi) + freed <=
+			node_secs + dent_secs + reserved_sections(sbi) + needed)
+		return true;
+	if (!has_curseg_enough_space(sbi, node_blocks, dent_blocks))
+		return true;
+	return false;
 }
 
 static inline bool f2fs_is_checkpoint_ready(struct f2fs_sb_info *sbi)
Signature · 1 line
2.32.0
maintainer
#1 lore raw
Quoted 9 lines · Chao Yu

As Yanming reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=215914

The root cause is: in a very small sized image, it's very easy to exceed threshold of foreground GC, if we calculate free space and dirty data based on section granularity, in corner case, has_not_enough_free_secs() will always return true, result in deadloop in f2fs_gc().

Performance regression was reported. Can we check this for very small sized image only?

Quoted 73 lines

So this patch refactors has_not_enough_free_secs() as below to fix this issue:
1. calculate needed space based on block granularity, and separate all blocks to two parts, section part, and block part, comparing section part to free section, and comparing block part to free space in openned log.
2. account F2FS_DIRTY_NODES, F2FS_DIRTY_IMETA and F2FS_DIRTY_DENTS as node block consumer;
3. account F2FS_DIRTY_DENTS as data block consumer;

Cc [email protected]
Reported-by Ming Yan <[email protected]>
Signed-off-by Chao Yu <[email protected]>
---
 fs/f2fs/segment.h | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)
fs/f2fs/segment.h +17 -13
index 8a591455d796..28f7aa9b40bf 100644
@@ -575,11 +575,10 @@ static inline int reserved_sections(struct f2fs_sb_info *sbi)
 	return GET_SEC_FROM_SEG(sbi, reserved_segments(sbi));
 }
 
-static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi)
+static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi,
+			unsigned int node_blocks, unsigned int dent_blocks)
 {
-	unsigned int node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
-					get_pages(sbi, F2FS_DIRTY_DENTS);
-	unsigned int dent_blocks = get_pages(sbi, F2FS_DIRTY_DENTS);
+
 	unsigned int segno, left_blocks;
 	int i;
 

@@ -605,19 +604,24 @@ static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi)
 static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
 					int freed, int needed)
 {
-	int node_secs = get_blocktype_secs(sbi, F2FS_DIRTY_NODES);
-	int dent_secs = get_blocktype_secs(sbi, F2FS_DIRTY_DENTS);
-	int imeta_secs = get_blocktype_secs(sbi, F2FS_DIRTY_IMETA);
+	unsigned int total_node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
+					get_pages(sbi, F2FS_DIRTY_DENTS) +
+					get_pages(sbi, F2FS_DIRTY_IMETA);
+	unsigned int total_dent_blocks = get_pages(sbi, F2FS_DIRTY_DENTS);
+	unsigned int node_secs = total_node_blocks / BLKS_PER_SEC(sbi);
+	unsigned int dent_secs = total_dent_blocks / BLKS_PER_SEC(sbi);
+	unsigned int node_blocks = total_node_blocks % BLKS_PER_SEC(sbi);
+	unsigned int dent_blocks = total_dent_blocks % BLKS_PER_SEC(sbi);
 
 	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
 		return false;
 
-	if (free_sections(sbi) + freed == reserved_sections(sbi) + needed &&
-			has_curseg_enough_space(sbi))
-		return false;
-	return (free_sections(sbi) + freed) <=
-		(node_secs + 2 * dent_secs + imeta_secs +
-		reserved_sections(sbi) + needed);
+	if (free_sections(sbi) + freed <=
+			node_secs + dent_secs + reserved_sections(sbi) + needed)
+		return true;
+	if (!has_curseg_enough_space(sbi, node_blocks, dent_blocks))
+		return true;
+	return false;
 }
 
 static inline bool f2fs_is_checkpoint_ready(struct f2fs_sb_info *sbi)
Signature · 1 line
2.32.0
author maintainer
#2 lore raw
Quoted 5 lines · Jaegeuk Kim
Quoted 4 lines · Chao Yu

As Yanming reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=215914

Quoted 8 lines
Quoted 5 lines

The root cause is: in a very small sized image, it's very easy to exceed threshold of foreground GC, if we calculate free space and dirty data based on section granularity, in corner case, has_not_enough_free_secs() will always return true, result in deadloop in f2fs_gc().

Performance regression was reported. Can we check this for very small sized image only?

I noticed that, I've fixed the issue in v2, could you please take a look?

Thanks,

Quoted 74 lines
Quoted 74 lines

So this patch refactors has_not_enough_free_secs() as below to fix this issue:
1. calculate needed space based on block granularity, and separate all blocks to two parts, section part, and block part, comparing section part to free section, and comparing block part to free space in openned log.
2. account F2FS_DIRTY_NODES, F2FS_DIRTY_IMETA and F2FS_DIRTY_DENTS as node block consumer;
3. account F2FS_DIRTY_DENTS as data block consumer;

Cc [email protected]
Reported-by Ming Yan <[email protected]>
Signed-off-by Chao Yu <[email protected]>
---
  fs/f2fs/segment.h | 30 +++++++++++++++++-------------
  1 file changed, 17 insertions(+), 13 deletions(-)
fs/f2fs/segment.h +17 -13
index 8a591455d796..28f7aa9b40bf 100644
@@ -575,11 +575,10 @@ static inline int reserved_sections(struct f2fs_sb_info *sbi)
  	return GET_SEC_FROM_SEG(sbi, reserved_segments(sbi));
  }
 
-static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi)
+static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi,
+			unsigned int node_blocks, unsigned int dent_blocks)
  {
-	unsigned int node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
-					get_pages(sbi, F2FS_DIRTY_DENTS);
-	unsigned int dent_blocks = get_pages(sbi, F2FS_DIRTY_DENTS);
+
  	unsigned int segno, left_blocks;
  	int i;
 

@@ -605,19 +604,24 @@ static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi)
  static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
  					int freed, int needed)
  {
-	int node_secs = get_blocktype_secs(sbi, F2FS_DIRTY_NODES);
-	int dent_secs = get_blocktype_secs(sbi, F2FS_DIRTY_DENTS);
-	int imeta_secs = get_blocktype_secs(sbi, F2FS_DIRTY_IMETA);
+	unsigned int total_node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
+					get_pages(sbi, F2FS_DIRTY_DENTS) +
+					get_pages(sbi, F2FS_DIRTY_IMETA);
+	unsigned int total_dent_blocks = get_pages(sbi, F2FS_DIRTY_DENTS);
+	unsigned int node_secs = total_node_blocks / BLKS_PER_SEC(sbi);
+	unsigned int dent_secs = total_dent_blocks / BLKS_PER_SEC(sbi);
+	unsigned int node_blocks = total_node_blocks % BLKS_PER_SEC(sbi);
+	unsigned int dent_blocks = total_dent_blocks % BLKS_PER_SEC(sbi);
 
  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
  		return false;
 
-	if (free_sections(sbi) + freed == reserved_sections(sbi) + needed &&
-			has_curseg_enough_space(sbi))
-		return false;
-	return (free_sections(sbi) + freed) <=
-		(node_secs + 2 * dent_secs + imeta_secs +
-		reserved_sections(sbi) + needed);
+	if (free_sections(sbi) + freed <=
+			node_secs + dent_secs + reserved_sections(sbi) + needed)
+		return true;
+	if (!has_curseg_enough_space(sbi, node_blocks, dent_blocks))
+		return true;
+	return false;
  }
 
  static inline bool f2fs_is_checkpoint_ready(struct f2fs_sb_info *sbi)
Signature · 1 line
2.32.0