linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: don't ignore writing pages on fsync during checkpoint=disable

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Message-ID: <d0a48947-e4df-9b0f-735e-6b306a64c4fe@kernel.org>
Date:   Wed, 25 Aug 2021 07:30:22 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: don't ignore writing pages on fsync
 during checkpoint=disable

On 2021/8/25 1:09, Jaegeuk Kim wrote:
> On 08/24, Chao Yu wrote:
>> On 2021/8/24 1:01, Jaegeuk Kim wrote:
>>> We must flush dirty pages when calling fsync() during checkpoint=disable.
>>> Returning zero makes inode being clear, which fails to flush them when
>>> enabling checkpoint back even by sync_inodes_sb().
>>
>> Without this patch, file can be persisted via checkpoint=enable as well, my
>> testcase:
>>
>> - mount -t f2fs -o checkpoint=disable,checkpoint_nomerge /dev/pmem0 /mnt/f2fs/
>> - cp file /mnt/f2fs/
>> - xfs_io /mnt/f2fs/file -c "fdatasync"
>> - mount -o remount,checkpoint=enable /dev/pmem0 /mnt/f2fs/
>> - umount /mnt/f2fs
>> - mount /dev/pmem0 /mnt/f2fs
>> - md5sum file /mnt/f2fs/file
>> chksum values are the same.
>>
>> Am I missing something?
> 
> I'm trying to address one subtle issue where a file has only NEW_ADDR by the

Oh, I doubt that we may failed to flush data of all inodes due to failures during
sync_inodes_sb(), additionally, how about adding retry logic for sync_inodes_sb()
if there is still any F2FS_DIRTY_DATA reference counts in f2fs_enable_checkpoint()
to mitigate this issue, e.g.:

f2fs_enable_checkpoint()

	do {
		sync_inode_sb();
		congestion_wait();
		cond_resched();
	} while (get_pages(sbi, F2FS_DIRTY_DATA) && retry_count--)

	if (get_pages(sbi, F2FS_DIRTY_DATA))
		f2fs_warm("");

Thanks,

> checkpoint=disable test. I don't think this hurts anything but can see
> some mitigation of the issue.
> 
>>
>> Thanks,