Ted Ts'o <tytso@xxxxxxx> writes: > On Wed, Aug 04, 2010 at 11:26:56AM -0400, Greg Freemyer wrote: >> >> Since the proposed patch is not aggregating discards into multiple >> ranges per ATA command, I thought some of the non-optimized devices >> would take minutes / hours? >> >> If true, a way to control the progress from userspace is important. >> >> If in general it is only going to take a few seconds for a full FITRIM >> to run, it is much less important, but I suppose the the RT project >> might find even that problematic. Few second may not being true, We always have to think about crazy user, and crazy fs-layouts. My SSD is able to process 8*10^3 requests per second So in worst case( where 1k fs block are bysy like this 010101010101) it can process about 10^3/s * 2*1Kb = 16Mb/s Which is no good. > > Even if it without the RT project, if disk activity is slowed or > completely stopped for a few seconds, I can think of plenty of > workloads where this would be totally unacceptable. Suppose you are > running a web site; it doesn't really matter whether it is at Google, > Facebook, Twitter, etc. If this means that one or more web pages get > stalled by "a few seconds" while the FITRIM is going on, this is > generally not considered acceptable. Even if it slows down the server > by 30-50%, for some sites this would also be quite unacceptable. > > This is a hard problem to solve, though, especially if there is an > insistence to solve it in a fs-independent fashion. I could imagine > doing this at work, by doing things one block group at a time, and > then I could measure, for our specific hardware, how badly disk > performance would get hit, and for how long, and then the userspace > daemon could control how many block groups to do per unit time. > But this would be of necessity ext2/3/4 specific.... > > So I'm not sure what to suggest here. Maybe the answer is we can have > a fs-independent ioctl for desktop workloads, and one which gives more > fine-grained control for those who need it? That seems ugly, but it > might be the best compromise. Why do we have to invent a wheel again? We already have BLKDISCARD which has following arguments: uint64_t range[2] So IMHO it is reasonable that FITRIM should have following arguments uint64_t start, uint64_t len, uint64_t minlen. No problems with compat, no problems with interactivity. User who does not care about interactivity may just call ioctl(fd, FITRIM, 0, LLONG_MAX, 0), > > - Ted > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
