On Tue, Nov 20, 2018 at 09:35:07PM -0800, Sagi Grimberg wrote: >> Given it is over TCP, I guess it should be doable for you to preallocate one >> 256-bvec table in one page for each request, then sets the max segment size as >> (unsigned int)-1, and max segment number as 256, the preallocated table >> should work anytime. > > 256 bvec table is really a lot to preallocate, especially when its not > needed, I can easily initialize the bvec_iter on the bio bvec. If this > involves preallocation of the worst-case than I don't consider this to > be an improvement. Ok, I took a look at the nvme-tcp code and it seems you care about bios because you want a contiguos bio chunk for sending it down the networking code. Yes, in that case we sort of need to iterate over bios. But you already have a special case for discard, so you don't really need any of the magic in the bio_bvecs() helper either can can just count bi_vcnt in the bio.
