Messages in this thread | | | Date | Sun, 16 Aug 2009 12:59:43 -0400 | From | Christoph Hellwig <> | Subject | Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) |
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On Sun, Aug 16, 2009 at 10:52:07AM -0500, James Bottomley wrote: > However, the enterprise has been doing UNMAP for a while, so we can draw > inferences from them since the SSD FTL will operate similarly. For > them, UNMAP is the same cost in terms of time regardless of the number > of extents. The reason is that it's moving the blocks from the global > in use list to the global free list. Part of the problem is that this > involves locking and quiescing, so UNMAP ends up being quite expensive > to the array but constant in terms of cost (hence they want as few > unmaps for as many sectors as possible).
How are they doing the unmaps? Using something similar to Mark's wiper script and using SG_IO? Because right now we do not actually implement UNMAP support in the kernel. I'd really love to test the XFS batched discard support with a real UNMAP implementation.
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