[PATCH] f2fs: modify f2fs_is_checkpoint_ready logic to allow more data to be written with the CP disable

[Qi Han]

When the free segment is used up during CP disable, many write or
ioctl operations will get ENOSPC error codes, even if there are
still many blocks available. We can reproduce it in the following
steps:

dd if=/dev/zero of=f2fs.img bs=1M count=55
mkfs.f2fs -f f2fs.img
mount f2fs.img f2fs_dir -o checkpoint=disable:10%
cd f2fs_dir
dd if=/dev/zero of=bigfile bs=1M count=50
sync
rm bigfile
i=1; while [[ $i -lt 10000000 ]]; do (file_name=./file$i; dd \
if=/dev/random of=$file_name bs=1M count=0); i=$((i+1)); done
stat -f ./

In f2fs_need_SSR() function, it is allowed to use SSR to allocate
blocks when CP is disabled, so in f2fs_is_checkpoint_ready function,
can we judge the number of invalid blocks when free segment is not
enough, and return ENOSPC only if the number of invalid blocks is
also not enough?

Signed-off-by: Qi Han <hanqi@xxxxxxxx>
---
 fs/f2fs/segment.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 71adb4a43bec..9bf0cf3a6a31 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -637,12 +637,33 @@ static inline bool has_enough_free_secs(struct f2fs_sb_info *sbi,
 	return !has_not_enough_free_secs(sbi, freed, needed);
 }
 
+static inline bool has_enough_available_blocks(struct f2fs_sb_info *sbi)
+{
+	unsigned int total_free_blocks = sbi->user_block_count -
+					valid_user_blocks(sbi) -
+					sbi->current_reserved_blocks;
+
+	if (total_free_blocks <= sbi->unusable_block_count)
+		total_free_blocks = 0;
+	else
+		total_free_blocks -= sbi->unusable_block_count;
+
+	if (total_free_blocks > F2FS_OPTION(sbi).root_reserved_blocks)
+		total_free_blocks -= F2FS_OPTION(sbi).root_reserved_blocks;
+	else
+		total_free_blocks = 0;
+
+	return (total_free_blocks > 0) ? true : false;
+}
+
 static inline bool f2fs_is_checkpoint_ready(struct f2fs_sb_info *sbi)
 {
 	if (likely(!is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
 		return true;
 	if (likely(has_enough_free_secs(sbi, 0, 0)))
 		return true;
+	if (likely(has_enough_available_blocks(sbi)))
+		return true;
 	return false;
 }
 
-- 
2.39.0