On Thu, Jul 5, 2018 at 6:25 PM, Dan Williams dan.j.williams@intel.com wrote:
On Thu, Jul 5, 2018 at 1:17 PM, Keith Busch keith.busch@intel.com wrote:
This patch will find the max contiguous area to determine the largest namespace size that can be created. If the requested size exceeds the largest available, ENOSPC error will be returned.
This fixes the allocation underrun error and wrong error return code that have otherwise been observed as the following kernel warning:
WARNING: CPU: <CPU> PID: <PID> at drivers/nvdimm/namespace_devs.c:913 size_store
Fixes: a1f3e4d6a0c3 ("libnvdimm, region: update nd_region_available_dpa() for multi-pmem support") Cc: stable@vger.kernel.org Signed-off-by: Keith Busch keith.busch@intel.com
v1 -> v2:
Updated changelog to indicate the warning this patch fixes and copy stable.
Fixed code comments with the correct name of a function
drivers/nvdimm/dimm_devs.c | 29 +++++++++++++++++++++++++++++ drivers/nvdimm/namespace_devs.c | 2 +- drivers/nvdimm/nd-core.h | 3 +++ drivers/nvdimm/region_devs.c | 23 +++++++++++++++++++++++ 4 files changed, 56 insertions(+), 1 deletion(-)
diff --git a/drivers/nvdimm/dimm_devs.c b/drivers/nvdimm/dimm_devs.c index 8d348b22ba45..791a93cd8eb1 100644 --- a/drivers/nvdimm/dimm_devs.c +++ b/drivers/nvdimm/dimm_devs.c @@ -536,6 +536,35 @@ resource_size_t nd_blk_available_dpa(struct nd_region *nd_region) return info.available; }
+/** x + * nd_pmem_max_contiguous_dpa - For the given dimm+region, return the max
contiguous unallocated dpa range.
- @nd_region: constrain available space check to this reference region
- @nd_mapping: container of dpa-resource-root + labels
- */
+resource_size_t nd_pmem_max_contiguous_dpa(struct nd_region *nd_region,
struct nd_mapping *nd_mapping)+{
struct nvdimm_drvdata *ndd = to_ndd(nd_mapping);resource_size_t start, end, max = 0;struct resource *res;if (!ndd)return 0;start = nd_mapping->start;end = start + nd_mapping->size;for_each_dpa_resource(ndd, res) {if ((res->start - start) > max)max = res->start - start;start = res->start + resource_size(res);}if (start < end && end - start > max)max = end - start;return max;+}
So, I liked how simple and straightforward this was, but the unit test reminded me how complicated the free space allocation could be given that we still might need to account for aliased BLK capacity.
A few things I now notice:
- It is possible for a dpa resource to start before nd_mapping->start
and/or end after nd_mapping->size. See the diagram in tools/testing/nvdimm/test/nfit.c
- We need to be summing the max extents across all DIMMs in the set
while also accounting for this BLK overlap problem that nd_pmem_available_dpa() handles.
The original bug arose from the fact that the nd_region_available_dpa() accounts for total busy capacity and the allocation path looks for extents. It would be nice to unify those two functions... or maybe standardize on scan_allocate() everywhere.
I think you can redo this using reserve_free_pmem() and then find the largest free space reservation after accounting for blk_max_overlap as calculated by nd_region_available_dpa().
reserve_free_pmem() inserts resources into the dpa resource tree with the name "pmem-reserve" then you need to filter those against blk_max_overlap to find which ones might appear free, but shadowed by a BLK allocation on one of the DIMMs in the set. Yes, it allocates memory and is heavy handed, but I'm having a hard time thinking of something better at the moment.