Re: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during writeback for various fses

Jan Kara [off-list ref] writes:

quoted

I see. So many block layer stuff sounds like broken on corner case? If
so, I more feel this approach should be temporary workaround, and should
use another less-blocking approach.

  Not many but some... The alternative to less blocking approach is to do
copy-out before a page is submitted for IO (or various middle ground
alternatives of doing sometimes copyout, sometimes blocking...). That costs
some performance as well. We talked about it at LSF and the approach
Darrick is implementing was considered the least intrusive. There's really
no way to fix these corner cases and keep performance.

You already considered, to copy only if page was writeback (like
copy-on-write). I.e. if page is on I/O, copy, then switch the page for
writing new data.

Yes, it is complex. But I think blocking and overhead is minimum, and
this can be used as infrastructure for copy-on-write FS.

Thanks.
-- 
OGAWA Hirofumi [off-list ref]

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