On Mon, Jun 05, 2017 at 11:17:49AM -0600, Jason Gunthorpe wrote: > On Mon, Jun 05, 2017 at 08:08:25PM +0300, Leon Romanovsky wrote: > > On Mon, Jun 05, 2017 at 11:44:00AM -0500, Christoph Lameter wrote: > > > On Wed, 10 May 2017, ahmad omary wrote: > > > > > > > We have considered using mmap(), but As the size of device memory may be limited > > > > ,the way to access it from host cpu may differ from vendor to vendor, due to > > > > the 4K (page) aligment limitation of mmap() and the need not to directly > > > > allow user to access the device memory, there is a need for a wrapper access > > > > methods API that allows allocating and managing chunks that are smaller than > > > > 4KB and not necessarily aligned to 4KB (page size). > > > > > > Why are 4k sized chunks a problem given that there are megabytes of memory > > > in these devices? We are using various adapters already with an mmapped > > > solution here. > > > > Ahmad presented use case where he needs access to small objects > > (semaphores) in large scale (MPI). 1MB in the granularity of 4k will give us > > 256 chunks only, and it is definitely not enough. > > Is 256 chunks per machine not enough? A single process could carve out > smaller regions from the 4k kernel allocation. It is rough calculation for 1MB, when I asked Ahmad about this limitation (4K) he explained to me that exposed device memory is less than 1MB. Thanks > > Jason > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
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