On Tue, Jan 21 2020 at 9:20am -0500, Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote: > On 21.01.2020 16:48, Mike Snitzer wrote: > > On Tue, Jan 21 2020 at 8:33am -0500, > > Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote: > > > >> On 21.01.2020 15:36, Kirill Tkhai wrote: > >>> On 21.01.2020 15:24, Mike Snitzer wrote: > >>>> On Tue, Jan 21 2020 at 5:42am -0500, > >>>> Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote: > >>>> > >>>>> Since dm inherits limits from underlining block devices, > >>>>> this patch directly disables max_allocate_sectors for dm > >>>>> till full allocation support is implemented. > >>>>> > >>>>> This prevents high-level primitives (generic_make_request_checks(), > >>>>> __blkdev_issue_write_zeroes(), ...) from sending REQ_ALLOCATE > >>>>> requests. > >>>>> > >>>>> Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> > >>>>> --- > >>>>> drivers/md/dm-table.c | 2 ++ > >>>>> drivers/md/md.h | 1 + > >>>>> 2 files changed, 3 insertions(+) > >>>> > >>>> You're mixing DM and MD changes in the same patch. > >>>> > >>>> But I'm wondering if it might be best to set this default for stacking > >>>> devices in blk_set_stacking_limits()? > >>>> > >>>> And then it is up to each stacking driver to override as needed. > >>> > >>> Hm. Sound like a good idea. This "lim->max_allocate_sectors = 0" in blk_set_stacking_limits() > >>> should work for dm's dm_calculate_queue_limits(), since it calls blk_stack_limits(), which is: > >>> > >>> t->max_allocate_sectors = min(t->max_allocate_sectors, > >>> b->max_allocate_sectors); > >>> > >>> Could you please tell is this fix is also enough for md? > >> > >> It looks like it's enough since queue defaults are set in md_alloc()->blk_set_stacking_limits(). > >> In case of we set "max_allocate_sectors = 0", in further it can be changed only manually, > >> but nobody does this. > > > > Yes, it will work to disable this capability for MD and DM. > > > > But if/when a stacked device _dooes_ want to support this then it'll be > > awkward to override this stacking default to allow blk_stack_limits() > > to properly stack up this limit. blk_limits are extremely fiddley so > > this isn't necessarily new. But by explicitly defaulting to 0 and then > > having blk_stack_limits use min() for this limit: it results in stacking > > drivers needing to clumsily unwind the default. E.g. DM will need to > > tweak its blk_stack_limits() related code to allow override that > > actually _does_ stack up the underlying devices' capability (and not > > just impose its own limit that ignores the underlying devices). > > > > So I'm not convinced this is the right way to go (be it the v4 approach > > you took or the cleaner use of blk_set_stacking_limits I suggested). > > Is there a strong vision about the way we should go? Or you leave this choose > up to me? I don't have time to work through it at the moment (e.g. implementing dm-thinp support to know what the block core code should be) so I'll just defer to you on a disabling it for now. > > And to be clear, I'm interested in having DM thinp support this > > capability to preallocate blocks. > > My opinion is it would be better to not mix several subsystem related > support in a single patch set. Both of the approaches (v4 or that you > suggested) do not prevents us to implement allocation support in next > patch series. After we have the base functionality enabled, we may add > support in other subsystems and drivers one by one with more focus > on the subsystem specificities and with the best possible attention. Yeah, I'm aware nothing is ever set in stone. Setting to 0 in blk_set_stacking_limits() is OK for now. Thanks, Mike
