Re: [PATCH] f2fs: allow out-place-update for direct IO in LFS mode

From: Chao Yu
Date: Tue Sep 18 2018 - 21:16:45 EST

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On 2018/9/19 0:27, Jaegeuk Kim wrote:
> 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@xxxxxxxxxx>
>>>>
>>>> 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.

As I explained above, even we always use buffered IO, there is no such
guarantee for serializing all async/sync IO in block layer, am I missing
something?

If you really don't want to change the logic for SMR, how about let me just
leave that case?

Thanks,

>
>>
>> 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@xxxxxxxxxx>
>>>> ---
>>>> 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
>>>
>>> .
>>>
>
> .
>

Next message: Alexandre Belloni: "[PATCH 1/2] rtc: test: make license text and module license match."
Previous message: Sergey Senozhatsky: "Re: [PATCH 14/33] vfs: Implement a filesystem superblock creation/configuration context [ver #11]"
In reply to: Jaegeuk Kim: "Re: [PATCH] f2fs: allow out-place-update for direct IO in LFS mode"
Next in thread: Jaegeuk Kim: "Re: [PATCH] f2fs: allow out-place-update for direct IO in LFS mode"
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