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linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jul 18, 2025 at 03:20:16PM +0530, Dev Jain wrote: > > On 18/07/25 2:32 pm, Dev Jain wrote: > > Use folio_pte_batch() to optimize change_pte_range(). On arm64, if the ptes > > are painted with the contig bit, then ptep_get() will iterate through all > > 16 entries to collect a/d bits. Hence this optimization will result in > > a 16x reduction in the number of ptep_get() calls. Next, > > ptep_modify_prot_start() will eventually call contpte_try_unfold() on > > every contig block, thus flushing the TLB for the complete large folio > > range. Instead, use get_and_clear_full_ptes() so as to elide TLBIs on > > each contig block, and only do them on the starting and ending > > contig block. > > > > For split folios, there will be no pte batching; the batch size returned > > by folio_pte_batch() will be 1. For pagetable split folios, the ptes will > > still point to the same large folio; for arm64, this results in the > > optimization described above, and for other arches, a minor improvement > > is expected due to a reduction in the number of function calls. > > > > mm-selftests pass on arm64. I have some failing tests on my x86 VM already; > > no new tests fail as a result of this patchset. > > > > We use the following test cases to measure performance, mprotect()'ing > > the mapped memory to read-only then read-write 40 times: > > > > Test case 1: Mapping 1G of memory, touching it to get PMD-THPs, then > > pte-mapping those THPs > > Test case 2: Mapping 1G of memory with 64K mTHPs > > Test case 3: Mapping 1G of memory with 4K pages > > > > Average execution time on arm64, Apple M3: > > Before the patchset: > > T1: 2.1 seconds T2: 2 seconds T3: 1 second > > > > After the patchset: > > T1: 0.65 seconds T2: 0.7 seconds T3: 1.1 seconds > > > > For the note: the numbers are different from the previous versions. > I must have run the test for more number of iterations and then > pasted the test program here for 40 iterations, that's why the mismatch. > Thanks for this clarification!