On Mon, Feb 06 2017 at 9:49pm -0500, Kent Overstreet <kent.overstreet@xxxxxxxxx> wrote: > On Mon, Feb 06, 2017 at 04:47:24PM -0900, Kent Overstreet wrote: > > On Mon, Feb 06, 2017 at 01:53:09PM +0100, Pavel Machek wrote: > > > Still there on v4.9, 36 threads on nokia n900 cellphone. > > > > > > So.. what needs to be done there? > > > But, I just got an idea for how to handle this that might be halfway sane, maybe > > I'll try and come up with a patch... > > Ok, here's such a patch, only lightly tested: > > -- >8 -- > Subject: [PATCH] block: Make rescuer threads per request_queue, not per bioset > > Note: this patch is very lightly tested. > > Also, trigger rescuing whenever with bios on current->bio_list, instead > of only when we block in bio_alloc_bioset(). This is more correct, and > should result in fewer rescuer threads. > > XXX: The current->bio_list plugging needs to be unified with the > blk_plug mechanism. > > TODO: If we change normal request_queue drivers to handle arbitrary size > bios by processing requests incrementally, instead of splitting bios, > then we can get rid of rescuer threads from those devices. Hi Kent, I really appreciate you working on this further. Thanks. As I think you're probably already aware, a long standing issue with the per bio_set rescuer is this bug (which manifests in dm-snapshot deadlocks): https://bugzilla.kernel.org/show_bug.cgi?id=119841 Please also see this patch header, from a private branch from a while ago, that describes the problem in detail: http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=cd2c760b5a609e2aaf3735a7b9503a953535c368 Would welcome your consideration of that BZ as you think further and/or iterate on this line of work. Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
