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

From: Chao Yu
Date: Thu Oct 17 2024 - 05:56:53 EST


On 2024/10/9 18:27, Qi Han wrote:
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?

Can you please try below patch?

From 38b7c97dcc55ba83de4220c3dc54c2eb66148dd5 Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@xxxxxxxxxx>
Date: Thu, 17 Oct 2024 17:07:05 +0800
Subject: [PATCH] f2fs: revalidate empty segment when checkpoint is disabled

If checkpoint is off, let's set segment as free once all newly
written datas were removed.

Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
---
fs/f2fs/segment.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index f8d6e601e084..9bad13d70afb 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -853,6 +853,17 @@ static void locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno)
valid_blocks = get_valid_blocks(sbi, segno, false);
ckpt_valid_blocks = get_ckpt_valid_blocks(sbi, segno, false);

+ /*
+ * If checkpoint is off, let's set segment as free once all newly
+ * written datas were removed.
+ */
+ if (is_sbi_flag_set(sbi, SBI_CP_DISABLED) &&
+ valid_blocks == 0 && ckpt_valid_blocks == 0) {
+ __remove_dirty_segment(sbi, segno, DIRTY);
+ __set_test_and_free(sbi, segno, false);
+ goto out_lock;
+ }
+
if (valid_blocks == 0 && (!is_sbi_flag_set(sbi, SBI_CP_DISABLED) ||
ckpt_valid_blocks == usable_blocks)) {
__locate_dirty_segment(sbi, segno, PRE);
@@ -863,7 +874,7 @@ static void locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno)
/* Recovery routine with SSR needs this */
__remove_dirty_segment(sbi, segno, DIRTY);
}
-
+out_lock:
mutex_unlock(&dirty_i->seglist_lock);
}

--
2.40.1


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;
}