On 21.01.2020 17:43, Mike Snitzer wrote: > 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. I get your point. Thanks for the suggestion and comments, Mike. Kirill
