Messages in this thread | | | Subject | Re: about TRIM/DISCARD support and barriers | From | James Bottomley <> | Date | Mon, 24 Nov 2008 07:52:56 +0900 |
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On Sun, 2008-11-23 at 13:39 +0000, David Woodhouse wrote: > > We don't attempt to put non-contiguous ranges into a single TRIM yet. > > We don't even merge contiguous ranges -- I still need to fix the > elevators to stop writes crossing writes,
I don't think we want to do that ... it's legal if the write isn't a barrier and it will inhibit merging. That may be just fine for a SSD, but it's not for spinning media since they get better performance out of merged writes.
> before we can stop discards > from also being barriers. (Discards are just writes, for the purpose of > that conversation).
Perhaps they shouldn't be ... they have different characteristics. For instance, a discard may cross a read or write that has no sectors in common with it; a discard may be merged as a non contiguous range (assuming the drive supports multiple ranges), etc.
I think it might be better to give it its own type for the elevators.
James
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