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

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Message-ID: <YSa2v7oLMAWZP+b5@google.com>
Date:   Wed, 25 Aug 2021 14:31:43 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...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 08/25, Chao Yu wrote:
> 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("");

Agreed. Sent v2.

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