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Date:   Fri, 27 May 2022 21:33:55 +0000
From:   Eric Biggers <ebiggers@kernel.org>
To:     Jaegeuk Kim <jaegeuk@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net,
        linux-block@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH] f2fs: add sysfs entry to avoid FUA
Message-ID: <YpFDw3mQjN1LBd2j@gmail.com>
References: <20220527205955.3251982-1-jaegeuk@kernel.org>
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[+Cc linux-block for FUA, and linux-xfs for iomap]

On Fri, May 27, 2022 at 01:59:55PM -0700, Jaegeuk Kim wrote:
> Some UFS storage gives slower performance on FUA than write+cache_flush.
> Let's give a way to manage it.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Should the driver even be saying that it has FUA support in this case?  If the
driver didn't claim FUA support, that would also solve this problem.

> ---
>  Documentation/ABI/testing/sysfs-fs-f2fs | 7 +++++++
>  fs/f2fs/data.c                          | 2 ++
>  fs/f2fs/f2fs.h                          | 1 +
>  fs/f2fs/sysfs.c                         | 2 ++
>  4 files changed, 12 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> index 9b583dd0298b..cd96b09d7182 100644
> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> @@ -434,6 +434,7 @@ Date:		April 2020
>  Contact:	"Daeho Jeong" <daehojeong@google.com>
>  Description:	Give a way to change iostat_period time. 3secs by default.
>  		The new iostat trace gives stats gap given the period.
> +
>  What:		/sys/fs/f2fs/<disk>/max_io_bytes
>  Date:		December 2020
>  Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
> @@ -442,6 +443,12 @@ Description:	This gives a control to limit the bio size in f2fs.
>  		whereas, if it has a certain bytes value, f2fs won't submit a
>  		bio larger than that size.
>  
> +What:		/sys/fs/f2fs/<disk>/no_fua_dio
> +Date:		May 2022
> +Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
> +Description:	This gives a signal to iomap, which should not use FUA for
> +		direct IOs. Default: 0.

iomap is an implementation detail, so it shouldn't be mentioned in UAPI
documentation.  UAPI documentation should describe user-visible behavior only.

> +
>  What:		/sys/fs/f2fs/<disk>/stat/sb_status
>  Date:		December 2020
>  Contact:	"Chao Yu" <yuchao0@huawei.com>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index f5f2b7233982..23486486eab2 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -4153,6 +4153,8 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  	if ((inode->i_state & I_DIRTY_DATASYNC) ||
>  	    offset + length > i_size_read(inode))
>  		iomap->flags |= IOMAP_F_DIRTY;
> +	if (F2FS_I_SB(inode)->no_fua_dio)
> +		iomap->flags |= IOMAP_F_DIRTY;

This is overloading the IOMAP_F_DIRTY flag to mean something other than dirty.
Perhaps this flag needs to be renamed, or a new flag should be added?

> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index e10838879538..c2400ea0080b 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1671,6 +1671,7 @@ struct f2fs_sb_info {
>  	int dir_level;				/* directory level */
>  	int readdir_ra;				/* readahead inode in readdir */
>  	u64 max_io_bytes;			/* max io bytes to merge IOs */
> +	int no_fua_dio;				/* avoid FUA in DIO */

Make this a bool?

> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> index 4c50aedd5144..24d628ca92cc 100644
> --- a/fs/f2fs/sysfs.c
> +++ b/fs/f2fs/sysfs.c
> @@ -771,6 +771,7 @@ F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, iostat_period_ms, iostat_period_ms);
>  #endif
>  F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, readdir_ra, readdir_ra);
>  F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, max_io_bytes, max_io_bytes);
> +F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, no_fua_dio, no_fua_dio);
>  F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, gc_pin_file_thresh, gc_pin_file_threshold);
>  F2FS_RW_ATTR(F2FS_SBI, f2fs_super_block, extension_list, extension_list);
>  #ifdef CONFIG_F2FS_FAULT_INJECTION
> @@ -890,6 +891,7 @@ static struct attribute *f2fs_attrs[] = {
>  #endif
>  	ATTR_LIST(readdir_ra),
>  	ATTR_LIST(max_io_bytes),
> +	ATTR_LIST(no_fua_dio),

Where is it validated that only valid values (0 or 1) can be written to this
file?

- Eric