On 23/09/2024 10:38, Yu Kuai wrote:
We need a new branch in read_balance() to choose a rdev with full
copy.
Sure, I do realize that the mirror'ing personalities need more
sophisticated error handling changes (than what I presented).
However, in raid1_read_request() we do the read_balance() and then
the bio_split() attempt. So what are you suggesting we do for the
bio_split() error? Is it to retry without the bio_split()?
To me bio_split() should not fail. If it does, it is likely ENOMEM
or some other bug being exposed, so I am not sure that retrying with
skipping bio_split() is the right approach (if that is what you are
suggesting).
bio_split_to_limits() is already called from md_submit_bio(), so here
bio should only be splitted because of badblocks or resync. We have to
return error for resync, however, for badblocks, we can still try to
find a rdev without badblocks so bio_split() is not needed. And we need
to retry and inform read_balance() to skip rdev with badblocks in this
case.
This can only happen if the full copy only exist in slow disks. This
really is corner case, and this is not related to your new error path by
atomic write. I don't mind this version for now, just something
I noticed if bio_spilit() can fail.
Hi Kuai,
I am just coming back to this topic now.
Previously I was saying that we should error and end the bio if we need
to split for an atomic write due to BB. Continued below..
Are you saying that some improvement needs to be made to the current
code for badblocks handling, like initially try to skip bio_split()?
Apart from that, what about the change in raid10_write_request(),
w.r.t error handling?
There, for an error in bio_split(), I think that we need to do some
tidy-up if bio_split() fails, i.e. undo increase in rdev->nr_pending
when looping conf->copies
BTW, feel free to comment in patch 6/6 for that.
Yes, raid1/raid10 write are the same. If you want to enable atomic write
for raid1/raid10, you must add a new branch to handle badblocks now,
otherwise, as long as one copy contain any badblocks, atomic write will
fail while theoretically I think it can work.
Can you please expand on what you mean by this last sentence, "I think
it can work".
Indeed, IMO, chance of encountering a device with BBs and supporting
atomic writes is low, so no need to try to make it work (if it were
possible) - I think that we just report EIO.
Thanks,
John
