From: Jason Gunthorpe Subject: Re: [PATCH 0/6] nouveau/hmm: add support for mapping large pages Date: Mon, 25 May 2020 10:41:18 -0300 Message-ID: <20200525134118.GA2536@ziepe.ca> References: <20200508192009.15302-1-rcampbell@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200508192009.15302-1-rcampbell-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ralph Campbell Cc: nouveau-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jerome Glisse , John Hubbard , Christoph Hellwig , Ben Skeggs , Andrew Morton , Shuah Khan List-Id: nouveau.vger.kernel.org On Fri, May 08, 2020 at 12:20:03PM -0700, Ralph Campbell wrote: > hmm_range_fault() returns an array of page frame numbers and flags for > how the pages are mapped in the requested process' page tables. The PFN > can be used to get the struct page with hmm_pfn_to_page() and the page size > order can be determined with compound_order(page) but if the page is larger > than order 0 (PAGE_SIZE), there is no indication that the page is mapped > using a larger page size. To be fully general, hmm_range_fault() would need > to return the mapping size to handle cases like a 1GB compound page being > mapped with 2MB PMD entries. However, the most common case is the mapping > size the same as the underlying compound page size. > This series adds a new output flag to indicate this so that callers know it > is safe to use a large device page table mapping if one is available. > Nouveau and the HMM tests are updated to use the new flag. > > Note that this series depends on a patch queued in Ben Skeggs' nouveau > tree ("nouveau/hmm: map pages after migration") and the patches queued > in Jason's HMM tree. > There is also a patch outstanding ("nouveau/hmm: fix nouveau_dmem_chunk > allocations") that is independent of the above and could be applied > before or after. Did Christoph and Matt's remarks get addressed here? I think ODP could use something like this, currently it checks every page to get back to the huge page size and this flag would optimze that Jason