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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 May 2025 16:27:17.2696 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c27efd19-76d6-4f64-8249-08dd9d3b58b9 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM4PEPF00027A6B.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR08MB5979 On 27/05/25 4:20 pm, Lorenzo Stoakes wrote: > I seem to recall we agreed you'd hold off on this until the mprotect work > was done :>) I see a lot of review there and was expecting a respin, unless Oh, my interpretation was that you requested to hold this off for a bit to get some review on the mprotect series first, apologies if you meant otherwise! I posted that one or so week before so I thought enough time has passed : ) > I'm mistaken? > > At any rate we're in the merge window now so it's maybe not quite as > important now :) > > We're pretty close to this being done anyway, just need some feedback on > points raised (obviously David et al. may have further comments). > > Thanks, Lorenzo > > On Tue, May 27, 2025 at 01:20:47PM +0530, Dev Jain wrote: >> Currently move_ptes() iterates through ptes one by one. If the underlying >> folio mapped by the ptes is large, we can process those ptes in a batch >> using folio_pte_batch(), thus clearing and setting the PTEs in one go. >> For arm64 specifically, this results in a 16x reduction in the number of >> ptep_get() calls (since on a contig block, ptep_get() on arm64 will iterate >> through all 16 entries to collect a/d bits), and we also elide extra TLBIs >> through get_and_clear_full_ptes, replacing ptep_get_and_clear. > OK this is more general than the stuff in 2/2, so you are doing this work > for page-table split large folios also. > > I do think this _should_ be fine for that unless I've missed something. At > any rate I've commented on this in 2/2. > >> Mapping 1M of memory with 64K folios, memsetting it, remapping it to >> src + 1M, and munmapping it 10,000 times, the average execution time >> reduces from 1.9 to 1.2 seconds, giving a 37% performance optimization, >> on Apple M3 (arm64). No regression is observed for small folios. >> >> The patchset is based on mm-unstable (6ebffe676fcf). >> >> Test program for reference: >> >> #define _GNU_SOURCE >> #include >> #include >> #include >> #include >> #include >> #include >> >> #define SIZE (1UL << 20) // 1M >> >> int main(void) { >> void *new_addr, *addr; >> >> for (int i = 0; i < 10000; ++i) { >> addr = mmap((void *)(1UL << 30), SIZE, PROT_READ | PROT_WRITE, >> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); >> if (addr == MAP_FAILED) { >> perror("mmap"); >> return 1; >> } >> memset(addr, 0xAA, SIZE); >> >> new_addr = mremap(addr, SIZE, SIZE, MREMAP_MAYMOVE | MREMAP_FIXED, addr + SIZE); >> if (new_addr != (addr + SIZE)) { >> perror("mremap"); >> return 1; >> } >> munmap(new_addr, SIZE); >> } >> >> } >> >> v2->v3: >> - Refactor mremap_folio_pte_batch, drop maybe_contiguous_pte_pfns, fix >> indentation (Lorenzo), fix cover letter description (512K -> 1M) >> >> v1->v2: >> - Expand patch descriptions, move pte declarations to a new line, >> reduce indentation in patch 2 by introducing mremap_folio_pte_batch(), >> fix loop iteration (Lorenzo) >> - Merge patch 2 and 3 (Anshuman, Lorenzo) >> - Fix maybe_contiguous_pte_pfns (Willy) >> >> Dev Jain (2): >> mm: Call pointers to ptes as ptep >> mm: Optimize mremap() by PTE batching >> >> mm/mremap.c | 57 +++++++++++++++++++++++++++++++++++++++-------------- >> 1 file changed, 42 insertions(+), 15 deletions(-) >> >> -- >> 2.30.2 >>