On Tue, Jul 21 2015 at 9:00pm -0400, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Wed, Jul 22, 2015 at 10:09:23AM +1000, Dave Chinner wrote: > > On Tue, Jul 21, 2015 at 01:47:53PM -0400, Mike Snitzer wrote: > > > On Tue, Jul 21 2015 at 11:34am -0400, Eric Sandeen <sandeen@xxxxxxxxxx> wrote: > > > > On 7/20/15 5:36 PM, Dave Chinner wrote: > > > > The issue we had discussed previously is that there is no agreement > > > > across block devices about whether ENOSPC is a permanent or temporary > > > > condition. Asking the admin to tune the fs to each block device's > > > > behavior sucks, IMHO. > > > > > > It does suck, but it beats the alternative of XFS continuing to do > > > nothing about the problem. > > > > Just a comment on that: doing nothing is better than doing the wrong > > thing and being stuck with it forever. :) > > > > > Disucssing more with Vivek, might be that XFS would be best served to > > > model what dm-thinp has provided with its 'no_space_timeout'. It > > > defaults to queueing IO for 60 seconds, once the timeout expires the > > > queued IOs getted errored. If set to 0 dm-thinp will queue IO > > > indefinitely. > > > > Yes, that's exactly what I proposed in the thread I referenced in > > my previous email, and what got stuck on the bikeshed wall because > > of these concerns about knob twiddling: > > > > http://oss.sgi.com/archives/xfs/2015-02/msg00346.html > > > > | e.g. if we need configurable error handling, it needs to be > > | configurable for different error types, and it needs to be > > | configurable on a per-mount basis. And it needs to be configurable > > | at runtime, not just at mount time. That kind of leads to using > > | sysfs for this. e.g. for each error type we ned to handle different > > | behaviour for: > > | > > | $ cat /sys/fs/xfs/vda/meta_write_errors/enospc/type > > | [transient] permanent > > | $ cat /sys/fs/xfs/vda/meta_write_errors/enospc/perm_timeout_seconds > > | 300 > > | $ cat > > | /sys/fs/xfs/vda/meta_write_errors/enospc/perm_max_retry_attempts > > | 50 > > | $ cat > > | /sys/fs/xfs/vda/meta_write_errors/enospc/transient_fail_at_umount > > | 1 > > > > I've rebased this patchset, and I'm cleaning it up now, so in a few > > days I'll have something for review, likely for the 4.3 merge > > window.... > > Just thinking a bit more on how to make this simpler to configure, > is there a simple way for the filesystem to determine the current > config of the dm thinp volume? i.e. if the dm-thinp volume is > configured to error out immediately on enospc, then XFS should > default to doing the same thing. having XFS be able to grab this > status at mount time and change the default ENOSPC error config from > transient to permanent on such dm-thinp volumes would go a long way > to making these configs Just Do The Right Thing on block dev enospc > errors... > > e.g. if dm-thinp is configured to queue for 60s and then fail on > ENOSPC, we want XFS to fail immediately on ENOSPC in metadata IO. If > dm-thinp is configured to ENOSPC instantly (i.e. no queueing) then > we want XFS to retry and use it's default retry maximums before > failing permanently. Yes, that'd be nice. But there isn't a way to easily get the DM thinp device's config from within the kernel (unless XFS wants to get into the business of issuing ioctls to DM devices.. unlikely). I could be persuaded to expose a per-device sysfs file to get the status (would avoid need for ioctl), e.g.: # cat /sys/block/dm-5/dm/status (but that doesn't _really_ help in-kernel access, awkward for filesystem code to be opening sysfs files!) SO userspace (mkfs.xfs) could easily check the thinp device's setup using 'dmsetup status <device>' (output will either contain 'queue_if_no_space' or 'error_if_no_space'). The DM thinp 'no_space_timeout' (applicable if queue_if_no_space) is a thinp global accessed using a module param: # cat /sys/module/dm_thin_pool/parameters/no_space_timeout 60 I'm open to considering alternative interfaces for getting you the info you need. I just don't have a great sense for what mechanism you'd like to use. Do we invent a new block device operations table method that sets values in a 'struct no_space_strategy' passed in to the blockdevice? -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
