On Fri, Aug 14, 2009 at 6:03 PM, Mark Lord<liml@xxxxxx> wrote: > James Bottomley wrote: >> >> On Thu, 2009-08-13 at 14:15 -0400, 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. >>> >>> (Big unknown: Where will the bitmap live between reboots? Require DM >>> volumes so we can have a dedicated bitmap volume in the mix to store >>> the bitmap to? Maybe on mount, the filesystem has to be scanned to >>> initially populate the bitmap? Other options?) >> >> I wouldn't really have it live anywhere. Discard is best effort; it's >> not required for fs integrity. As long as we don't discard an in-use >> block we're free to do anything else (including forget to discard, >> rediscard a discarded block etc). >> >> It is theoretically possible to run all of this from user space using >> the fs mappings, a bit like a defrag command. > > .. > > Already a work-in-progress -- see my wiper.sh script on the hdparm page > at sourceforge. Trimming 50+GB of free space on a 120GB Vertex > (over 100 million sectors) takes a *single* TRIM command, > and completes in only a couple of seconds. > > Cheers > Mark, What filesystems does your script support? Running a tool like this in the middle of the night makes a lot of since to me even from the perspective of many / most enterprise users. How do prevent a race where a block becomes used between userspace asking status and it sending the discard request? ps: I tried to pull wiper.sh straight from sourceforge, but I'm getting some crazy page asking all sorts of questions and not letting me bypass it. I hope sourceforge is broken. The other option is they meant to do this. :( Greg -- Greg Freemyer -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
