On Thu, Aug 13, 2009 at 4:44 PM, <david@xxxxxxx> wrote: > On Thu, 13 Aug 2009, Greg Freemyer wrote: > >> On Thu, Aug 13, 2009 at 12:33 PM, <david@xxxxxxx> wrote: >>> >>> On Thu, 13 Aug 2009, Markus Trippelsdorf wrote: >>> >>>> On Thu, Aug 13, 2009 at 08:13:12AM -0700, Matthew Wilcox wrote: >>>>> >>>>> I am planning a complete overhaul of the discard work. Users can send >>>>> down discard requests as frequently as they like. The block layer will >>>>> cache them, and invalidate them if writes come through. Periodically, >>>>> the block layer will send down a TRIM or an UNMAP (depending on the >>>>> underlying device) and get rid of the blocks that have remained >>>>> unwanted >>>>> in the interim. >>>> >>>> That is a very good idea. I've tested your original TRIM implementation >>>> on >>>> my Vertex yesterday and it was awful ;-). The SSD needs hundreds of >>>> milliseconds to digest a single TRIM command. And since your >>>> implementation >>>> sends a TRIM for each extent of each deleted file, the whole system is >>>> unusable after a short while. >>>> An optimal solution would be to consolidate the discard requests, bundle >>>> them and send them to the drive as infrequent as possible. >>> >>> or queue them up and send them when the drive is idle (you would need to >>> keep track to make sure the space isn't re-used) >>> >>> as an example, if you would consider spinning down a drive you don't hurt >>> performance by sending accumulated trim commands. >>> >>> David Lang >> >> An alternate approach is the block layer maintain its own bitmap of >> used unused sectors / blocks. Unmap commands from the filesystem just >> cause the bitmap to be updated. No other effect. > > how does the block layer know what blocks are unused by the filesystem? > > or would it be a case of the filesystem generating discard/trim requests to > the block layer so that it can maintain it's bitmap, and then the block > layer generating the requests to the drive below it? Perhaps an interface (ioctl, etc) can be added to ask a filesystem to discard all unused blocks in a certain range? (That is, have the filesystem validate the request under any necessary locks before passing it to the block IO layer) -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
