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envelope-from=jgg@nvidia.com; helo=NAM10-BN7-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Nov 28, 2022 at 11:50:03AM -0700, Alex Williamson wrote: > There's a claim here about added complexity that I'm not really seeing. > It looks like we simply make an ioctl call here and scale our buffer > based on the minimum of the returned device estimate or our upper > bound. I'm not keen on this, for something like mlx5 that has a small precopy size and large post-copy size it risks running with an under allocated buffer, which is harmful to performance. It is a mmap space, if we don't touch the pages they don't get allocated from the OS, I think this is micro-optimizing. Jason