Unexpected SU+J inconsistency AGAIN -- please, don't shift topic to ZFS!

[Ivan Voras]

On 28/02/2013 15:56, Lev Serebryakov wrote:

>   One time, Kirk say, that delayed writes are Ok for SU until bottom
>  layer doesn't lie about operation completeness. geom_raid5 could
>  delay writes (in hope that next writes will combine nicely and allow
>  not to do read-calculate-write cycle for read alone), but it never
>  mark BIO complete until it is really completed (layers down to
>  geom_raid5 returns completion). So, every BIO in wait queue is "in
>  flight" from GEOM/VFS point of view. Maybe, it is fatal for journal :(

It shouldn't be - it could be a bug.

>   And want I really want to see is "SYNC" flag for BIO and that all
>  journal-related writes will be marked with it. Also all commits
>  originated with fsync() MUST be marked in same way, really. Alexander
>  Motin (ahci driver author) assured me, that he'll add support for
>  such flag in driver to flush drive cache too, if it will be
>  introduced.

Hmmm, once upon a time I actually tried to add it:

http://people.freebsd.org/~ivoras/diffs/fsync_flush.patch

This is from 2011, and was never really reviewed. Kirk said it was a
good idea (meaning the implementation could be wrong, YMMV) :)


I don't know whether it's significant, but ffs_softdep.c contains 6
bawrite() calls (meaning buf async write), in softdep_process_journal(),
softdep_journal_freeblocks(), softdep_fsync_mountdev(), sync_cgs(), and
flush_deplist().

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