On 2/18/19 4:08 PM, jianchao.wang wrote:
> Hi Bob
>
> On 2/13/19 5:50 PM, Bob Liu wrote:
>> Motivation:
>> When fs data/metadata checksum mismatch, lower block devices may have other
>> correct copies. e.g. If XFS successfully reads a metadata buffer off a raid1 but
>> decides that the metadata is garbage, today it will shut down the entire
>> filesystem without trying any of the other mirrors. This is a severe
>> loss of service, and we propose these patches to have XFS try harder to
>> avoid failure.
>>
>> This patch prototype this mirror retry idea by:
>> * Adding @nr_mirrors to struct request_queue which is similar as
>> blk_queue_nonrot(), filesystem can grab device request queue and check max
>> mirrors this block device has.
>> Helper functions were also added to get/set the nr_mirrors.
>>
>> * Introducing bi_rd_hint just like bi_write_hint, but bi_rd_hint is a long bitmap
>> in order to support stacked layer case.
>
> Why does we need a bitmap to know which underlying device has been tried ?
> For example, the following scenario,
>
> md8
> / | \
> sda sdb sdc
>
> If the the raid read the data from sda and fs check and find the data is corrupted.
> Then we may just need to let raid1 know that the data is from sda. Then based on this
> hint, raid1 could handle it with handle_read_error to try other replica and fix the
> error.
This doesn't work.
The md raid1 can only see IO success or failure, so fix_read_error won't fix this.
Sorry for the noise.
Thanks
Jianchao
>
> If this is feasible, we just need to modify the bio as following and needn't add any
> bytes in it.
>
> struct bio {
> ...
> union {
> unsigned short bi_write_hint;
> unsigned short bi_read_hint;
> }
> ...
> }
>
> Thanks
> Jianchao
>>
>> * Modify md/raid1 to support this retry feature.
>>
>> * Adapter xfs to use this feature.
>> If the read verify fails, we loop over the available mirrors and retry the read.
>>
>> * Rewrite retried read
>> When the read verification fails, but the retry succeedes
>> write the buffer back to correct the bad mirror
>>
>> * Add tracepoints and logging to alternate device retry.
>> This patch adds new log entries and trace points to the alternate device retry
>> error path.
>>
>> Changes v2:
>> - No more reuse bi_write_hint
>> - Stacked layer support(see patch 4/9)
>> - Other feedback fix
>>
>> Allison Henderson (5):
>> Add b_alt_retry to xfs_buf
>> xfs: Add b_rd_hint to xfs_buf
>> xfs: Add device retry
>> xfs: Rewrite retried read
>> xfs: Add tracepoints and logging to alternate device retry
>>
>> Bob Liu (4):
>> block: add nr_mirrors to request_queue
>> block: add rd_hint to bio and request
>> md:raid1: set mirrors correctly
>> md:raid1: rd_hint support and consider stacked layer case
>>
>> Documentation/block/biodoc.txt | 3 +
>> block/bio.c | 1 +
>> block/blk-core.c | 4 ++
>> block/blk-merge.c | 6 ++
>> block/blk-settings.c | 24 +++++++
>> block/bounce.c | 1 +
>> drivers/md/raid1.c | 123 ++++++++++++++++++++++++++++++++-
>> fs/xfs/xfs_buf.c | 58 +++++++++++++++-
>> fs/xfs/xfs_buf.h | 14 ++++
>> fs/xfs/xfs_trace.h | 6 +-
>> include/linux/blk_types.h | 1 +
>> include/linux/blkdev.h | 4 ++
>> include/linux/types.h | 3 +
>> 13 files changed, 244 insertions(+), 4 deletions(-)
>>
>
