> On Aug 7, 2017, at 7:40 AM, Xiangdong <[email protected]> wrote: > > Hi Barry, > > Thanks for your response. So these extra allocated memory is just a waste of > memory, but no harm for other mat related computation. Is it correct?
Yes, and given how virtual memory works with pages it isn't even much of a waste of memory. > > Thank you. > > Xiangdong > > On Fri, Aug 4, 2017 at 4:52 PM, Barry Smith <[email protected]> wrote: > > > On Aug 4, 2017, at 2:52 PM, Xiangdong <[email protected]> wrote: > > > > Hello everyone, > > > > I have a quick questions on the MatMPIAIJSetPreallocation. If we do not > > pass the exact number of nonzeros for o_nnz and d_nnz, (for example, > > MAT_INFO_NZ_ALLOCATED is 50% more than MAT_INFO_NZ_USED), will the > > performance of MatMult be affected? What effect will these allocated but > > unused memory cause? > > It is not a big deal to have extra memory, it won't slow things down. If > you under estimate it can slow things down a lot. > > > > > Thank you. > > > > Best, > > Xiangdong > >
