Messages in this thread | | | Date | Tue, 28 Nov 2017 16:11:54 +0800 | From | alex chen <> | Subject | Re: [Ocfs2-devel] [PATCH 2/3] ocfs2: add ocfs2_overwrite_io function |
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Hi Gang,
On 2017/11/28 15:38, Gang He wrote: > Hi Alex, > > >>>> >> Hi Gang, >> >> On 2017/11/28 13:33, Gang He wrote: >>> Hello Alex, >>> >>> >>>>>> >>>> Hi Gang, >>>> >>>> On 2017/11/27 17:46, Gang He wrote: >>>>> Add ocfs2_overwrite_io function, which is used to judge if >>>>> overwrite allocated blocks, otherwise, the write will bring extra >>>>> block allocation overhead. >>>>> >>>>> Signed-off-by: Gang He <ghe@suse.com> >>>>> --- >>>>> fs/ocfs2/extent_map.c | 67 >>>> +++++++++++++++++++++++++++++++++++++++++++++++++++ >>>>> fs/ocfs2/extent_map.h | 3 +++ >>>>> 2 files changed, 70 insertions(+) >>>>> >>>>> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c >>>>> index e4719e0..98bf325 100644 >>>>> --- a/fs/ocfs2/extent_map.c >>>>> +++ b/fs/ocfs2/extent_map.c >>>>> @@ -832,6 +832,73 @@ int ocfs2_fiemap(struct inode *inode, struct >>>> fiemap_extent_info *fieinfo, >>>>> return ret; >>>>> } >>>>> >>>>> +/* Is IO overwriting allocated blocks? */ >>>>> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len, >>>>> + int wait) >>>>> +{ >>>>> + int ret = 0, is_last; >>>>> + u32 mapping_end, cpos; >>>>> + struct ocfs2_super *osb = OCFS2_SB(inode->i_sb); >>>>> + struct buffer_head *di_bh = NULL; >>>>> + struct ocfs2_extent_rec rec; >>>>> + >>>>> + if (wait) >>>>> + ret = ocfs2_inode_lock(inode, &di_bh, 0); >>>>> + else >>>>> + ret = ocfs2_try_inode_lock(inode, &di_bh, 0); >>>>> + if (ret) >>>>> + goto out; >>>>> + >>>>> + if (wait) >>>>> + down_read(&OCFS2_I(inode)->ip_alloc_sem); >>>>> + else { >>>>> + if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) { >>>>> + ret = -EAGAIN; >>>>> + goto out_unlock1; >>>>> + } >>>>> + } >>>>> + >>>>> + if ((OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) && >>>>> + ((map_start + map_len) <= i_size_read(inode))) >>>>> + goto out_unlock2; >>>>> + >>>>> + cpos = map_start >> osb->s_clustersize_bits; >>>>> + mapping_end = ocfs2_clusters_for_bytes(inode->i_sb, >>>>> + map_start + map_len); >>>>> + is_last = 0; >>>>> + while (cpos < mapping_end && !is_last) { >>>>> + ret = ocfs2_get_clusters_nocache(inode, di_bh, cpos, >>>>> + NULL, &rec, &is_last); >>>>> + if (ret) { >>>>> + mlog_errno(ret); >>>>> + goto out_unlock2; >>>>> + } >>>>> + >>>>> + if (rec.e_blkno == 0ULL) >>>>> + break; >>>> I think here the blocks is not overwrite, because the hold is found and the >>>> blocks >>>> should be allocated. >>> If the rec.e_blkno == NULL, this means there is a hole. >>> The file hole means that these blocks are not allocated, it does not like >> unwritten block. >>> The unwritten blocks means that these blocks are allocated, but still have >> not been unwritten. >>> >> If we break the loop when we find the hold, out of this function we will >> allocate the blocks in >> ocfs2_file_write_iter()->..->ocfs2_direct_IO->__blockdev_direct_IO->..->ocfs2_dio_wr_g >> et_block() >> ->ocfs2_write_begin_nolock. Does this violate the semantics of 'IOCB_NOWAIT'; > Yes, then we need to check if this is a overwrite before doing direct-io. >
I mean here we should return 0 instead of break and we should immediately return -EAGAIN to upper apps, otherwise, some block allocation will be happen, which violates the semantics of 'IOCB_NOWAIT'.
Thanks, Alex
>> >> BTW, should we consider the down_write() and ocfs2_inode_lock() in >> ocfs2_dio_wr_get_block() when >> the flag 'IOCB_NOWAIT' is set; > I think that we should not consider that layer lock, otherwise, the code change will become more and more complex and big. > I also refer to ext4 file system code change for this feature(728fbc0e10b7f3ce2ee043b32e3453fd5201c055), they did not do any change in that layer. >
OK.
> Thanks > Gang > >> >>>>> + >>>>> + if (rec.e_flags & OCFS2_EXT_REFCOUNTED) >>>>> + break; >>>>> + >>>>> + cpos = le32_to_cpu(rec.e_cpos) + >>>>> + le16_to_cpu(rec.e_leaf_clusters); >>>>> + } >>>>> + >>>>> + if (cpos < mapping_end) >>>>> + ret = 1; >>>>> + >>>>> +out_unlock2: >>>> >>>> I think the 'out_up_read' is more readable than the 'out_unlock2' . >>> Ok, I will use more readable tag here. >>>> >>>>> + brelse(di_bh); >>>>> + >>>>> + up_read(&OCFS2_I(inode)->ip_alloc_sem); >>>>> + >>>>> +out_unlock1: >>>> >>>> We should release buffer head here. >>>> >>>>> + ocfs2_inode_unlock(inode, 0); >>>>> + >>>>> +out: >>>>> + return (ret ? 0 : 1); >>>>> +} >>>>> + >>>>> int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int >>>> whence) >>>>> { >>>>> struct inode *inode = file->f_mapping->host; >>>>> diff --git a/fs/ocfs2/extent_map.h b/fs/ocfs2/extent_map.h >>>>> index 67ea57d..fd9e86a 100644 >>>>> --- a/fs/ocfs2/extent_map.h >>>>> +++ b/fs/ocfs2/extent_map.h >>>>> @@ -53,6 +53,9 @@ int ocfs2_extent_map_get_blocks(struct inode *inode, u64 >>>> v_blkno, u64 *p_blkno, >>>>> int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, >>>>> u64 map_start, u64 map_len); >>>>> >>>>> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len, >>>>> + int wait); >>>>> + >>>>> int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int >>>> origin); >>>>> >>>>> int ocfs2_xattr_get_clusters(struct inode *inode, u32 v_cluster, >>>>> >>> >>> >>> . >>> > > . >
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