On Tue, Mar 18 2014 at 3:41am -0400, Shaohua Li <shli@xxxxxxxxxx> wrote: > On Mon, Mar 17, 2014 at 04:00:40PM -0400, Mike Snitzer wrote: > > > > I folded your changes in, and then committed a patch ontop that cleans > > some code up. But added 2 FIXMEs that still speak to pretty fundamental > > problems with the architecture of the dm-insitu-comp target, see: > > https://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=for-3.15-insitu-comp&id=8565ab6b04837591d03c94851c2f9f9162ce12f4 > > > > Unfortunately the single insitu_comp_wq workqueue that all insitu-comp > > targets are to share isn't a workable solution. Each target needs to > > have resource isolation from other targets (imagine insitu-comp used for > > multiple SSDs). This is important for suspend too because you'll need > > to flush/stop the workqueue. > > Is this just because of suspend? I didn't see fundamental reason why the > workqueue can't be shared even for several targets. I'm not seeing how you are guaranteeing that all queued work is completed during suspend. insitu_comp_queue_req() just calls queue_work_on(). BTW, queue_work_on()'s comment above its implementation says: "We queue the work to a specific CPU, the caller must ensure it can't go away." -- you're not able to insure a cpu isn't hotplugged so... but I also see you've used it in your raid5 perf improvement changes so you obviously have experience with using this interface. > > You introduced a state machine for tracking suspending, suspended, > > resumed. This really isn't necessary. During suspend you need to > > flush_workqueue(). On resume you shouldn't need to do anything special. > > > > As I noted in the commit, the thin and cache targets can serve as > > references for how you can manage the workqueue across suspend/resume > > and the lifetime of these workqueues relative to .ctr and .dtr. > > As far as I checking the code, .postsuspend is called after all requests are > finished. This already guarantees no pending requests running in insitu-comp > workqueue. I could easily be missing something obvious, but I don't see where that guarantee is implemented. > Doing a workqueue flush isn't required. The writeback thread is > running in background and waiting for requests completion can't guarantee the > thread isn't running, so we must make sure it is safely parked. Sure, but you don't need a state machine to do that. The DM core takes care of calling these hooks, so you just need to stop the writeback thread during suspend and (re)start/kick it on resume (preresume). -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
