[Ocfs2-devel] [PATCH v2] ocfs2: Fix start offset to ocfs2_zero_range_for_truncate()
Ashish Samant
ashish.samant at oracle.com
Mon Aug 29 21:11:34 PDT 2016
Hmm, thats weird. I see this on 4.7 kernel without the patch:
# xfs_io -c 'pwrite -b 4k 0 10M' -f 10MBfile
wrote 10485760/10485760 bytes at offset 0
10 MiB, 2560 ops; 0.0000 sec (683.995 MiB/sec and 175102.5992 ops/sec)
# reflink -f 10MBfile reflnktest
# fallocate -p -o 0 -l 1048615 reflnktest
# dd if=10MBfile iflag=direct bs=1048576 count=1 | hexdump -C
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.0321517 s, 32.6 MB/s
00100000
and with patch
----
# dd if=10MBfile iflag=direct bs=1M count=1 | hexdump -C
00000000 cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd
|................|
*
1+0 records in
1+0 records out
00100000
Thanks,
Ashish
On 08/29/2016 08:33 PM, Eric Ren wrote:
> Hello,
>
> On 08/30/2016 03:23 AM, Ashish Samant wrote:
>> Hi Eric,
>>
>> The easiest way to reproduce this is :
>>
>> 1. Create a random file of say 10 MB
>> xfs_io -c 'pwrite -b 4k 0 10M' -f 10MBfile
>> 2. Reflink it
>> reflink -f 10MBfile reflnktest
>> 3. Punch a hole at starting at cluster boundary with range greater
>> that 1MB. You can also use a range that will put the end offset in
>> another extent.
>> fallocate -p -o 0 -l 1048615 reflnktest
>> 4. sync
>> 5. Check the first cluster in the source file. (It will be zeroed out).
>> dd if=10MBfile iflag=direct bs=<cluster size> count=1 | hexdump -C
>
> Thanks! I have a try myself, but I'm not sure what is our expected
> output and if the test result meet
> it:
>
> 1. After applying this patch:
> ocfs2dev1:/mnt/ocfs2 # rm 10MBfile reflnktest
> ocfs2dev1:/mnt/ocfs2 # xfs_io -c 'pwrite -b 4k 0 10M' -f 10MBfile
> wrote 10485760/10485760 bytes at offset 0
> 10 MiB, 2560 ops; 0.0000 sec (1.089 GiB/sec and 285427.5839 ops/sec)
> ocfs2dev1:/mnt/ocfs2 # reflink -f 10MBfile reflnktest
> ocfs2dev1:/mnt/ocfs2 # fallocate -p -o 0 -l 1048615 reflnktest
> ocfs2dev1:/mnt/ocfs2 # dd if=10MBfile iflag=direct bs=1048576 count=1
> | hexdump -C
> 00000000 cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd
> |................|
> *
> 1+0 records in
> 1+0 records out
> 1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0952464 s, 11.0 MB/s
> 00100000
>
> 2. Before this patch:
> ....
> ocfs2dev1:/mnt/ocfs2 # dd if=10MBfile iflag=direct bs=1048576 count=1
> | hexdump -C
> 00000000 cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd
> |................|
> *
> 1+0 records in
> 1+0 records out
> 1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0954648 s, 11.0 MB/s
> 00100000
>
> 3. debugfs.ocfs2 -R stats /dev/sdb
> ...
> Block Size Bits: 12 Cluster Size Bits: 20
> ...
>
> Eric
>>
>> Thanks,
>> Ashish
>>
>> On 08/28/2016 10:39 PM, Eric Ren wrote:
>>> Hi,
>>>
>>> Thanks for this fix. I'd like to reproduce this issue locally and
>>> test this patch,
>>> could you elaborate the detailed steps of reproduction?
>>>
>>> Thanks,
>>> Eric
>>>
>>> On 08/27/2016 07:04 AM, Ashish Samant wrote:
>>>> If we punch a hole on a reflink such that following conditions are
>>>> met:
>>>>
>>>> 1. start offset is on a cluster boundary
>>>> 2. end offset is not on a cluster boundary
>>>> 3. (end offset is somewhere in another extent) or
>>>> (hole range > MAX_CONTIG_BYTES(1MB)),
>>>>
>>>> we dont COW the first cluster starting at the start offset. But in
>>>> this
>>>> case, we were wrongly passing this cluster to
>>>> ocfs2_zero_range_for_truncate() to zero out. This will modify the
>>>> cluster
>>>> in place and zero it in the source too.
>>>>
>>>> Fix this by skipping this cluster in such a scenario.
>>>>
>>>> Reported-by: Saar Maoz <saar.maoz at oracle.com>
>>>> Signed-off-by: Ashish Samant <ashish.samant at oracle.com>
>>>> Reviewed-by: Srinivas Eeda <srinivas.eeda at oracle.com>
>>>> ---
>>>> v1->v2:
>>>> -Changed the commit msg to include a better and generic description of
>>>> the problem, for all cluster sizes.
>>>> -Added Reported-by and Reviewed-by tags.
>>>> fs/ocfs2/file.c | 34 ++++++++++++++++++++++++----------
>>>> 1 file changed, 24 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>>>> index 4e7b0dc..0b055bf 100644
>>>> --- a/fs/ocfs2/file.c
>>>> +++ b/fs/ocfs2/file.c
>>>> @@ -1506,7 +1506,8 @@ static int ocfs2_zero_partial_clusters(struct
>>>> inode *inode,
>>>> u64 start, u64 len)
>>>> {
>>>> int ret = 0;
>>>> - u64 tmpend, end = start + len;
>>>> + u64 tmpend = 0;
>>>> + u64 end = start + len;
>>>> struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>>> unsigned int csize = osb->s_clustersize;
>>>> handle_t *handle;
>>>> @@ -1538,18 +1539,31 @@ static int
>>>> ocfs2_zero_partial_clusters(struct inode *inode,
>>>> }
>>>> /*
>>>> - * We want to get the byte offset of the end of the 1st cluster.
>>>> + * If start is on a cluster boundary and end is somewhere in
>>>> another
>>>> + * cluster, we have not COWed the cluster starting at start,
>>>> unless
>>>> + * end is also within the same cluster. So, in this case, we
>>>> skip this
>>>> + * first call to ocfs2_zero_range_for_truncate() truncate and
>>>> move on
>>>> + * to the next one.
>>>> */
>>>> - tmpend = (u64)osb->s_clustersize + (start &
>>>> ~(osb->s_clustersize - 1));
>>>> - if (tmpend > end)
>>>> - tmpend = end;
>>>> + if ((start & (csize - 1)) != 0) {
>>>> + /*
>>>> + * We want to get the byte offset of the end of the 1st
>>>> + * cluster.
>>>> + */
>>>> + tmpend = (u64)osb->s_clustersize +
>>>> + (start & ~(osb->s_clustersize - 1));
>>>> + if (tmpend > end)
>>>> + tmpend = end;
>>>> - trace_ocfs2_zero_partial_clusters_range1((unsigned long
>>>> long)start,
>>>> - (unsigned long long)tmpend);
>>>> + trace_ocfs2_zero_partial_clusters_range1(
>>>> + (unsigned long long)start,
>>>> + (unsigned long long)tmpend);
>>>> - ret = ocfs2_zero_range_for_truncate(inode, handle, start,
>>>> tmpend);
>>>> - if (ret)
>>>> - mlog_errno(ret);
>>>> + ret = ocfs2_zero_range_for_truncate(inode, handle, start,
>>>> + tmpend);
>>>> + if (ret)
>>>> + mlog_errno(ret);
>>>> + }
>>>> if (tmpend < end) {
>>>> /*
>>>
>>>
>>
>
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