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bh=g9RvAI6uRrnZhaoxjUI04YdZRMrZ80xSpJJR25dnKgk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=gQo+D8FKH6tXI3+ox34wHy8t/QPnafy7eFKiPdN54CFWadsZCuuDbANMx8GdTqvUU 2XLBLWTPdI2YrYHD1cwmJb+4MHHAn2OBq3xpcNt3lu30i1lauXgLD6ox6cBOq7jZgb 7iEvYSxeR4KiIXLuw2sqk5y2l7hyYBAIZGoKQpuo= Date: Fri, 17 Mar 2023 16:39:36 -0700 From: Andrew Morton To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Matthew Wilcox , Vlastimil Babka Subject: Re: [PATCH 0/2] Refactor do_fault_around() Message-Id: <20230317163936.06d9c7d032a5c2296075caa1@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A264B1C0014 X-Stat-Signature: 4dis6xizg6s9n5g63atkumd7j3htcy5o X-Rspam-User: X-HE-Tag: 1679096378-516655 X-HE-Meta: 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 J5KT+wU0 WwZalCGcdJFXCG9agwWOsNKeHohLZGRy0sI2VXCMaOJo7hwpG+qS2g7lT+TylOq5w3Vi6ePEjy8Fm0fWrwGWFZDixH0uP7xJiAjCiyTSr3JIHBWt/+e/c8WzVY2+IEIMNgJfOqekCGTS1+vVLResJTIIhz8Ur35pCQM9kyceLCAr+KGjNqd4Ln9+Jqm63YSOxa5lxcpajngGuFnYxzF0S5l0IvxqI6YdEqREQ11rkvnSai+sMwBL27HkppFNl9+X52joBVRl8Dpep5p73O5DskiQozdxOBshiaILX/YfrtnGlTTxxLjRV6sOL6YLqmx4R8VvOBkSYT9siG0N3sE6FYZI1f7myzJa3Oq44sAs+Am9hH4toecBOP18dhLOwIMvDFGZcOC4KjdUIFHBQw3Jqz5Ve5sfDpuAdphNO X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 17 Mar 2023 21:58:24 +0000 Lorenzo Stoakes wrote: > Refactor do_fault_around() to avoid bitwise tricks and arather difficult to > follow logic. Additionally, prefer fault_around_pages to > fault_around_bytes as the operations are performed at a base page > granularity. > > I have run this code against a small program I wrote which generates > significant input data and compares output with the original function to > ensure that it behaves the same as the old code across varying vmf, vma and > fault_around_pages inputs. Well, what changes were you looking for in that testing? do_fault_around() could become a no-op and most tests wouldn't notice. What we'd be looking for to test these changes is performance differences. Perhaps one could add a tracepoint to do_fault_around()'s call to ->map_pages, check that the before-and-after traces are identical. Or, if you're old school and lazy, if (!strcmp(current->comm, "name-of-my-test-program")) printk("name-of-my-test-program: %lu %lu\n", start_pgoff, end_pgoff) then grep-n-diff the dmesg output.