Patch series "Optimize mprotect() for large folios", v5. 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 Observing T1/T2 and T3 before the patchset, we also remove the regression introduced by ptep_get() on a contpte block. And, for large folios we get an almost 74% performance improvement, albeit the trade-off being a slight degradation in the small folio case. For x86: Before the patchset: T1: 3.75 seconds T2: 3.7 seconds T3: 3.85 seconds After the patchset: T1: 3.7 seconds T2: 3.7 seconds T3: 3.9 seconds So there is a minor improvement due to reduction in number of function calls, and a slight degradation in the small folio case due to the overhead of vm_normal_folio() + folio_test_large(). Here is the test program: #define _GNU_SOURCE #include <sys/mman.h> #include <stdlib.h> #include <string.h> #include <stdio.h> #include <unistd.h> #define SIZE (1024*1024*1024) unsigned long pmdsize = (1UL << 21); unsigned long pagesize = (1UL << 12); static void pte_map_thps(char *mem, size_t size) { size_t offs; int ret = 0; /* PTE-map each THP by temporarily splitting the VMAs. */ for (offs = 0; offs < size; offs += pmdsize) { ret |= madvise(mem + offs, pagesize, MADV_DONTFORK); ret |= madvise(mem + offs, pagesize, MADV_DOFORK); } if (ret) { fprintf(stderr, "ERROR: mprotect() failed\n"); exit(1); } } int main(int argc, char *argv[]) { char *p; int ret = 0; p = mmap((1UL << 30), SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (p != (1UL << 30)) { perror("mmap"); return 1; } memset(p, 0, SIZE); if (madvise(p, SIZE, MADV_NOHUGEPAGE)) perror("madvise"); explicit_bzero(p, SIZE); pte_map_thps(p, SIZE); for (int loops = 0; loops < 40; loops++) { if (mprotect(p, SIZE, PROT_READ)) perror("mprotect"), exit(1); if (mprotect(p, SIZE, PROT_READ|PROT_WRITE)) perror("mprotect"), exit(1); explicit_bzero(p, SIZE); } } This patch (of 7): Reduce indentation by refactoring the prot_numa case into a new function. No functional change intended. Link: https://lkml.kernel.org/r/20250718090244.21092-1-dev.jain@arm.com Link: https://lkml.kernel.org/r/20250718090244.21092-2-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Barry Song <baohua@kernel.org> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Lance Yang <ioworker0@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Cc: Yang Shi <yang@os.amperecomputing.com> Cc: Yicong Yang <yangyicong@hisilicon.com> Cc: Zhenhua Huang <quic_zhenhuah@quicinc.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>