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Date:   Thu, 12 May 2022 14:57:34 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <chao@kernel.org>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, Chao Yu <chao.yu@oppo.com>
Subject: Re: [PATCH] f2fs: separate NOCoW and pinfile semantics
Message-ID: <Yn2CztiJUY2UAjnd@google.com>
References: <20220512082116.2991611-1-chao@kernel.org>
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On 05/12, Chao Yu wrote:
> Pinning a file is heavy, because skipping pinned files make GC
> running with heavy load or no effect.
> 
> So that this patch proposes to separate nocow and pinfile semantics:
> - NOCoW flag can only be set on regular file.
> - NOCoW file will only trigger IPU at common writeback/flush.
> - NOCow file will do OPU during GC.
> 
> This flag can satisfying the demand of:
> 1) avoiding fragment of file's physical block
> 2) userspace doesn't want to pin file's physical address
> 
> Signed-off-by: Chao Yu <chao.yu@oppo.com>
> ---
>  fs/f2fs/data.c |  3 ++-
>  fs/f2fs/f2fs.h |  1 +
>  fs/f2fs/file.c | 25 ++++++++++++++++++++++++-
>  3 files changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 54a7a8ad994d..c8eab78f7d89 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2495,7 +2495,8 @@ bool f2fs_should_update_inplace(struct inode *inode, struct f2fs_io_info *fio)
>  	if (is_inode_flag_set(inode, FI_ALIGNED_WRITE))
>  		return false;
>  
> -	if (f2fs_is_pinned_file(inode))
> +	if (f2fs_is_pinned_file(inode) ||
> +			F2FS_I(inode)->i_flags & F2FS_NOCOW_FL)
>  		return true;
>  
>  	/* if this is cold file, we should overwrite to avoid fragmentation */
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 492af5b96de1..e91ece55f5e8 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -2916,6 +2916,7 @@ static inline void f2fs_change_bit(unsigned int nr, char *addr)
>  #define F2FS_NOCOMP_FL			0x00000400 /* Don't compress */
>  #define F2FS_INDEX_FL			0x00001000 /* hash-indexed directory */
>  #define F2FS_DIRSYNC_FL			0x00010000 /* dirsync behaviour (directories only) */
> +#define F2FS_NOCOW_FL			0x00800000 /* Do not cow file */
>  #define F2FS_PROJINHERIT_FL		0x20000000 /* Create with parents projid */
>  #define F2FS_CASEFOLD_FL		0x40000000 /* Casefolded file */
>  
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 09287876dbb7..7f92a3a157f7 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1851,6 +1851,20 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
>  	if (IS_NOQUOTA(inode))
>  		return -EPERM;
>  
> +	if ((iflags ^ masked_flags) & F2FS_NOCOW_FL) {
> +		int ret;
> +
> +		if (!S_ISREG(inode->i_mode))
> +			return -EINVAL;
> +		if (f2fs_should_update_outplace(inode, NULL))
> +			return -EINVAL;
> +		if (f2fs_is_pinned_file(inode))
> +			return -EINVAL;
> +		ret = f2fs_convert_inline_inode(inode);
> +		if (ret)
> +			return ret;
> +	}
> +
>  	if ((iflags ^ masked_flags) & F2FS_CASEFOLD_FL) {
>  		if (!f2fs_sb_has_casefold(F2FS_I_SB(inode)))
>  			return -EOPNOTSUPP;
> @@ -1926,6 +1940,7 @@ static const struct {
>  	{ F2FS_NOCOMP_FL,	FS_NOCOMP_FL },
>  	{ F2FS_INDEX_FL,	FS_INDEX_FL },
>  	{ F2FS_DIRSYNC_FL,	FS_DIRSYNC_FL },
> +	{ F2FS_NOCOW_FL,	FS_NOCOW_FL },
>  	{ F2FS_PROJINHERIT_FL,	FS_PROJINHERIT_FL },
>  	{ F2FS_CASEFOLD_FL,	FS_CASEFOLD_FL },
>  };
> @@ -1957,7 +1972,8 @@ static const struct {
>  		FS_NOCOMP_FL |		\
>  		FS_DIRSYNC_FL |		\
>  		FS_PROJINHERIT_FL |	\
> -		FS_CASEFOLD_FL)
> +		FS_CASEFOLD_FL |	\
> +		FS_NOCOW_FL)
>  
>  /* Convert f2fs on-disk i_flags to FS_IOC_{GET,SET}FLAGS flags */
>  static inline u32 f2fs_iflags_to_fsflags(u32 iflags)
> @@ -3081,6 +3097,13 @@ static int f2fs_ioc_set_pin_file(struct file *filp, unsigned long arg)
>  
>  	inode_lock(inode);
>  
> +	if (F2FS_I(inode)->i_flags & F2FS_NOCOW_FL) {
> +		f2fs_info(F2FS_I_SB(inode), "inode (%lu) is already NOCOW one",
> +			inode->i_ino);
> +		ret = -EINVAL;

Why rejecting this? We can pin the file to get 2MB-aligned allocation on the
NOCOW file.

> +		goto out;
> +	}
> +
>  	if (!pin) {
>  		clear_inode_flag(inode, FI_PIN_FILE);
>  		f2fs_i_gc_failures_write(inode, 0);
> -- 
> 2.25.1