On Mon, Jun 03, 2019 at 10:46:08AM -0400, Mike Snitzer wrote: > On Mon, Jun 03 2019 at 10:18am -0400, > zhangyi (F) <yi.zhang@xxxxxxxxxx> wrote: > > > Currently, although we submit super bios in log-write thread orderly > > (the super.nr_entries is incremented by each logged entry), the > > submit_bio() cannot make sure that each super sector is written to log > > device in order. So the submitting bio of each super sector may be > > out-of-order, and then the final nr_entries maybe small than the real > > entries submitted. > > > > This problem can be reproduced by the xfstests generic/455 with ext4, > > which may complained below after running the test: > > > > QA output created by 455 > > -Silence is golden > > +mark 'end' does not exist > > > > This patch serialize submitting super secotrs to make sure each super > > sectors are written to log disk in order. > > > > Signed-off-by: zhangyi (F) <yi.zhang@xxxxxxxxxx> > > This doesn't feel right. > > You raised 2 things you're trying to address: > 1) IO is out of order > 2) accounting (nr_entries) isn't correct > > I'll need to reviewer closer but serializing "super" bios doesn't seem > like the best fix. > > Josef, any chance you can weigh in on this? AFAIK you are still "the > man" for dm-log-writes ;) > Well the #2 is caused by #1, we submit the bio for a super two times in a row and it's a crapshoot which one makes it to disk. So he's right, and it's kind of funny because this is the sort of problem that dm-log-writes was written to catch, and I fucked it up here ;). That being said this is a bit over-engineered, can we just add a completion to the log buff and do a wait_for_completion() when we're writing out the super? It's not like this thing needs to be super performant. Thanks, Josef -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
