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

[OGAWA Hirofumi]

Jan Kara <jack@xxxxxxx> writes:

>> 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 <hirofumi@xxxxxxxxxxxxxxxxxx>
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