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Date: Tue, 18 Sep 2018 09:27:19 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: Chao Yu <chao@...nel.org>, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: allow out-place-update for direct IO in LFS mode
On 09/18, Chao Yu wrote:
> On 2018/9/18 9:27, Jaegeuk Kim wrote:
> > On 09/16, Chao Yu wrote:
> >> From: Chao Yu <yuchao0@...wei.com>
> >>
> >> Normally, DIO uses in-pllace-update, but in LFS mode, f2fs doesn't
> >> allow triggering any in-place-update writes, so we fallback direct
> >> write to buffered write, result in bad performance of large size
> >> write.
> >
> > I remember this is to serialize all the IOs in one buffered IO path to keep
> > the IO sequence espeicially useful for SMR drivers. Could you confirm whether
> > there is any IO reordering problem?
>
> IMO, buffered IO will encounter reordering issue more easily, for example:
>
> User write 2mb data via DIO, but according to policy on LFS mode, it will
> fallback to buffered IO.
>
> Before dio triggers writeback, an async writeback from background is
> triggered, so all IO distribution can be:
>
> page LBA range
> async IO: 0 - 255 x + 0, x + 255
> sync IO: 256 - 511 x + 256, x + 511
>
> Then block IO scheduler can issue sync IO before async IO, result IO
> reordering.
>
> Anyway, in DIO path we will suffer less IO reordering issue.
My concern was on mixed DIO and buffered IOs where we don't have a way to
serialize all the IOs.
>
> Thanks,
>
> >
> >>
> >> This patch adds to support triggering out-place-update for direct IO
> >> to enhance its performance.
> >>
> >> Note that it needs to exclude direct read IO during direct write,
> >> since new data writing to new block address will no be valid until
> >> write finished.
> >>
> >> storage: zram
> >>
> >> time xfs_io -f -d /mnt/f2fs/file -c "pwrite 0 1073741824" -c "fsync"
> >>
> >> Before:
> >> real 0m13.061s
> >> user 0m0.327s
> >> sys 0m12.486s
> >>
> >> After:
> >> real 0m6.448s
> >> user 0m0.228s
> >> sys 0m6.212s
> >>
> >> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> >> ---
> >> fs/f2fs/data.c | 41 +++++++++++++++++++++++++++++++++--------
> >> fs/f2fs/f2fs.h | 39 +++++++++++++++++++++++++++++++++++----
> >> fs/f2fs/file.c | 3 ++-
> >> 3 files changed, 70 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >> index 048f9cf1d589..9937dc2f384a 100644
> >> --- a/fs/f2fs/data.c
> >> +++ b/fs/f2fs/data.c
> >> @@ -894,7 +894,7 @@ static int __allocate_data_block(struct dnode_of_data *dn, int seg_type)
> >>
> >> dn->data_blkaddr = datablock_addr(dn->inode,
> >> dn->node_page, dn->ofs_in_node);
> >> - if (dn->data_blkaddr == NEW_ADDR)
> >> + if (dn->data_blkaddr != NULL_ADDR)
> >> goto alloc;
> >>
> >> if (unlikely((err = inc_valid_block_count(sbi, dn->inode, &count))))
> >> @@ -950,7 +950,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
> >>
> >> if (direct_io) {
> >> map.m_seg_type = f2fs_rw_hint_to_seg_type(iocb->ki_hint);
> >> - flag = f2fs_force_buffered_io(inode, WRITE) ?
> >> + flag = f2fs_force_buffered_io(inode, iocb, from) ?
> >> F2FS_GET_BLOCK_PRE_AIO :
> >> F2FS_GET_BLOCK_PRE_DIO;
> >> goto map_blocks;
> >> @@ -1069,7 +1069,15 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
> >> goto sync_out;
> >> }
> >>
> >> - if (!is_valid_data_blkaddr(sbi, blkaddr)) {
> >> + if (is_valid_data_blkaddr(sbi, blkaddr)) {
> >> + /* use out-place-update for driect IO under LFS mode */
> >> + if (test_opt(sbi, LFS) && create &&
> >> + flag == F2FS_GET_BLOCK_DEFAULT) {
> >> + err = __allocate_data_block(&dn, map->m_seg_type);
> >> + if (!err)
> >> + set_inode_flag(inode, FI_APPEND_WRITE);
> >> + }
> >> + } else {
> >> if (create) {
> >> if (unlikely(f2fs_cp_error(sbi))) {
> >> err = -EIO;
> >> @@ -2491,36 +2499,53 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> >> struct address_space *mapping = iocb->ki_filp->f_mapping;
> >> struct inode *inode = mapping->host;
> >> struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >> + struct f2fs_inode_info *fi = F2FS_I(inode);
> >> size_t count = iov_iter_count(iter);
> >> loff_t offset = iocb->ki_pos;
> >> int rw = iov_iter_rw(iter);
> >> int err;
> >> enum rw_hint hint = iocb->ki_hint;
> >> int whint_mode = F2FS_OPTION(sbi).whint_mode;
> >> + bool lock_read;
> >>
> >> err = check_direct_IO(inode, iter, offset);
> >> if (err)
> >> return err < 0 ? err : 0;
> >>
> >> - if (f2fs_force_buffered_io(inode, rw))
> >> + if (f2fs_force_buffered_io(inode, iocb, iter))
> >> return 0;
> >>
> >> + lock_read = allow_outplace_dio(inode, iocb, iter);
> >> +
> >> trace_f2fs_direct_IO_enter(inode, offset, count, rw);
> >>
> >> if (rw == WRITE && whint_mode == WHINT_MODE_OFF)
> >> iocb->ki_hint = WRITE_LIFE_NOT_SET;
> >>
> >> - if (!down_read_trylock(&F2FS_I(inode)->i_gc_rwsem[rw])) {
> >> - if (iocb->ki_flags & IOCB_NOWAIT) {
> >> + if (iocb->ki_flags & IOCB_NOWAIT) {
> >> + if (!down_read_trylock(&fi->i_gc_rwsem[rw])) {
> >> + iocb->ki_hint = hint;
> >> + err = -EAGAIN;
> >> + goto out;
> >> + }
> >> + if (lock_read && !down_read_trylock(&fi->i_gc_rwsem[READ])) {
> >> + up_read(&fi->i_gc_rwsem[rw]);
> >> iocb->ki_hint = hint;
> >> err = -EAGAIN;
> >> goto out;
> >> }
> >> - down_read(&F2FS_I(inode)->i_gc_rwsem[rw]);
> >> + } else {
> >> + down_read(&fi->i_gc_rwsem[rw]);
> >> + if (lock_read)
> >> + down_read(&fi->i_gc_rwsem[READ]);
> >> }
> >>
> >> err = blockdev_direct_IO(iocb, inode, iter, get_data_block_dio);
> >> - up_read(&F2FS_I(inode)->i_gc_rwsem[rw]);
> >> +
> >> + if (lock_read)
> >> + up_read(&fi->i_gc_rwsem[READ]);
> >> +
> >> + up_read(&fi->i_gc_rwsem[rw]);
> >>
> >> if (rw == WRITE) {
> >> if (whint_mode == WHINT_MODE_OFF)
> >> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >> index 6f59ad180be7..a6dc9d581ee4 100644
> >> --- a/fs/f2fs/f2fs.h
> >> +++ b/fs/f2fs/f2fs.h
> >> @@ -8,6 +8,7 @@
> >> #ifndef _LINUX_F2FS_H
> >> #define _LINUX_F2FS_H
> >>
> >> +#include <linux/uio.h>
> >> #include <linux/types.h>
> >> #include <linux/page-flags.h>
> >> #include <linux/buffer_head.h>
> >> @@ -3461,11 +3462,41 @@ static inline bool f2fs_may_encrypt(struct inode *inode)
> >> #endif
> >> }
> >>
> >> -static inline bool f2fs_force_buffered_io(struct inode *inode, int rw)
> >> +static inline int block_unaligned_IO(struct inode *inode,
> >> + struct kiocb *iocb, struct iov_iter *iter)
> >> {
> >> - return (f2fs_post_read_required(inode) ||
> >> - (rw == WRITE && test_opt(F2FS_I_SB(inode), LFS)) ||
> >> - F2FS_I_SB(inode)->s_ndevs);
> >> + unsigned int i_blkbits = READ_ONCE(inode->i_blkbits);
> >> + unsigned int blocksize_mask = (1 << i_blkbits) - 1;
> >> + loff_t offset = iocb->ki_pos;
> >> + unsigned long align = offset | iov_iter_alignment(iter);
> >> +
> >> + return align & blocksize_mask;
> >> +}
> >> +
> >> +static inline int allow_outplace_dio(struct inode *inode,
> >> + struct kiocb *iocb, struct iov_iter *iter)
> >> +{
> >> + struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >> + int rw = iov_iter_rw(iter);
> >> +
> >> + return (test_opt(sbi, LFS) && (rw == WRITE) &&
> >> + !block_unaligned_IO(inode, iocb, iter));
> >> +}
> >> +
> >> +static inline bool f2fs_force_buffered_io(struct inode *inode,
> >> + struct kiocb *iocb, struct iov_iter *iter)
> >> +{
> >> + struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >> + int rw = iov_iter_rw(iter);
> >> +
> >> + if (f2fs_post_read_required(inode))
> >> + return true;
> >> + if (sbi->s_ndevs)
> >> + return true;
> >> + if (test_opt(sbi, LFS) && (rw == WRITE) &&
> >> + block_unaligned_IO(inode, iocb, iter))
> >> + return true;
> >> + return false;
> >> }
> >>
> >> #ifdef CONFIG_F2FS_FAULT_INJECTION
> >> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >> index 428e7398bd89..70491631e040 100644
> >> --- a/fs/f2fs/file.c
> >> +++ b/fs/f2fs/file.c
> >> @@ -3018,7 +3018,8 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
> >> if (!f2fs_overwrite_io(inode, iocb->ki_pos,
> >> iov_iter_count(from)) ||
> >> f2fs_has_inline_data(inode) ||
> >> - f2fs_force_buffered_io(inode, WRITE)) {
> >> + f2fs_force_buffered_io(inode,
> >> + iocb, from)) {
> >> clear_inode_flag(inode,
> >> FI_NO_PREALLOC);
> >> inode_unlock(inode);
> >> --
> >> 2.18.0
> >
> > .
> >
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