Messages in this thread | | | Date | Thu, 23 Jun 2016 21:49:30 -0400 | From | Mike Snitzer <> | Subject | Re: [PATCH v3 3/4] dm: add infrastructure for DAX support |
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On Thu, Jun 23 2016 at 7:36pm -0400, Kani, Toshimitsu <toshi.kani@hpe.com> wrote:
> On Thu, 2016-06-23 at 17:05 -0400, Mike Snitzer wrote: > : > > +static int device_supports_dax(struct dm_target *ti, struct dm_dev *dev, > > + sector_t start, sector_t len, void *data) > > +{ > > + struct request_queue *q = bdev_get_queue(dev->bdev); > > + > > + return q && blk_queue_dax(q); > > +} > > + > > +static bool dm_table_supports_dax(struct dm_table *t) > > +{ > > + struct dm_target *ti; > > + unsigned i = 0; > > + > > + /* Ensure that all targets support DAX. */ > > + while (i < dm_table_get_num_targets(t)) { > > + ti = dm_table_get_target(t, i++); > > + > > + if (!ti->type->direct_access) > > + return false; > > + > > + if (!ti->type->iterate_devices || > > + !ti->type->iterate_devices(ti, device_supports_dax, > > NULL)) > > + return false; > > + } > > + > > + return true; > > +} > > + > > Hi Mike, > > Thanks for the update. I have a question about the above change. Targets may > have their own parameters. For instance, dm-stripe has 'chunk_size', which is > checked in stripe_ctr(). DAX adds additional restriction that chunk_size > needs to be aligned by page size. So, I think we need to keep target > responsible to verify if DAX can be supported. What do you think?
We've never had to concern the dm-stripe target with hardware specific chunk_size validation. The user is able to specify the chunk_size via lvm2's lvcreate -I argument. Yes this gives users enough rope to hang themselves but it is very easy to configure a dm-stripe device with the appropriate chunk size (PAGE_SIZE) from userspace.
But lvm2 could even be trained to make sure the chunk_size is a factor of physical_block_size (PAGE_SIZE in the case of pmem) if the underlying devices export queue/dax=1
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