On Wed, May 04 2011 at 12:50pm -0400, Martin K. Petersen <martin.petersen@xxxxxxxxxx> wrote: > >>>>> "Mike" == Mike Snitzer <snitzer@xxxxxxxxxx> writes: > > Mike> lim->discard_zeroes_data = -1; was suspect to me too. > Mike> But why default to 1 here? > > Because otherwise DM would default to having dzd to "unsupported", > meaning the feature would never be turned on regardless of the bottom > device capabilities. > > The old approach used the -1 value to indicate "has not been set". That > was only really intended as a value for the stacking drivers, not for > the LLDs. It was a bit of a hack and I'd rather deal with dzd the same > way as we do with clustering. > > > >> @@ -166,6 +166,7 @@ void blk_queue_make_request(struct request_queue > >> *q, make_request_fn *mfn) > >> > >> blk_set_default_limits(&q->limits); > >> blk_queue_max_hw_sectors(q, BLK_SAFE_MAX_SECTORS); > >> + q->limits.discard_zeroes_data = 0; > >> > >> /* > >> * by default assume old behaviour and bounce for any highmem page > > Mike> Only to then reset to 0 here? Shouldn't we default to 0 and only > Mike> set to 1 where applicable (e.g. sd_config_discard)? > > My first approach was to set it in dm-table.c before stacking. But I > thought it was icky to have the stacking driver ask for defaults and > then have to tweak them for things to work correctly. > > The other option is to have blk_set_default_stacking_limits(). Or we > could add a flag to blk_set_default_limits to indicate whether this is a > LLD or a stacking driver. > > We already special-case BLK_SAFE_MAX_SECTORS when setting the request > function. And that's the only non-stacking user of the default limits > call. So that's why I disabled dzd there. Since this is a stable bugfix > I also wanted to keep it small and simple. But I'm totally open to > suggestions. Your current approach sounds good. Might be good to briefly speak to the duality of the stacking vs non-stacking approach in the associated patch header. Thanks for clarifying. Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
