On 09/12/2013 02:47 PM, Theodore Ts'o wrote:
On Thu, Sep 12, 2013 at 10:52:38AM -0500, Eric Sandeen wrote:
However, it seems a little odd to me that ext4 feels it necessary to issue
discards on blocks which have been fallocated but not written to, I'll have
to think about that part (doesn't really matter for your case, it's just a
curiosity).
For fstrim, we issue discards based on blocks which are not in use
according to the block allocation bitmap.
It shouldn't matter that we've issued discard on blocks which had been
previously discarded, and in fact, it might help, since sometimes
storage devices only traces block usage on large granularities ---
that is, it might only releases blocks on a thin provisioned storage
when a full megabyte worth of blocks are discarded.
- Ted
It is the right thing to do to re-issue the trims I think for exactly that
reason. Devices are allowed by the spec to ignore requests that are not aligned
to their needs, so this lets us try to get back in sync.
ric
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