Messages in this thread | | | Date | Tue, 28 Nov 2017 21:22:13 +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 16:32, Gang He wrote: > Hi Alex, > > >>>> >> 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'. > Before we do a direct-io, I need to check if this is a overwrite allocated blocks IO. > If not, we will return -EAGAIN in 'IOCB_NOWAIT' mode. this should not trigger any block allocation. > I am not sure if we understand your concern totally. >
Yes, your description is correct. So we should return 0 instead of break when we find the hold in ocfs2_overwrite_io();
> Thanks > Gang > >> >> 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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