[PATCH 0/9] mm/rmap: Optimize anonymous large folio unmapping

[Dev Jain]

Speed up unmapping of anonymous large folios by clearing the ptes, and
setting swap ptes, in one go.

The following benchmark (stolen from Barry at [1]) is used to measure the
time taken to swapout 256M worth of memory backed by 64K large folios:

 #define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
 #include <errno.h>

 #define SIZE_MB 256
 #define SIZE_BYTES (SIZE_MB * 1024 * 1024)

 int main() {
     void *addr = mmap(NULL, SIZE_BYTES, PROT_READ | PROT_WRITE,
                       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
     if (addr == MAP_FAILED) {
         perror("mmap failed");
         return 1;
     }

     memset(addr, 0, SIZE_BYTES);

     struct timespec start, end;
     clock_gettime(CLOCK_MONOTONIC, &start);

     if (madvise(addr, SIZE_BYTES, MADV_PAGEOUT) != 0) {
         perror("madvise(MADV_PAGEOUT) failed");
         munmap(addr, SIZE_BYTES);
         return 1;
     }

     clock_gettime(CLOCK_MONOTONIC, &end);

     long duration_ns = (end.tv_sec - start.tv_sec) * 1e9 +
                        (end.tv_nsec - start.tv_nsec);
     printf("madvise(MADV_PAGEOUT) took %ld ns (%.3f ms)\n",
            duration_ns, duration_ns / 1e6);

     munmap(addr, SIZE_BYTES);
     return 0;
 }

On arm64, only showing one of the middle values in the distribution:

without patch:
madvise(MADV_PAGEOUT) took 52192959 ns (52.193 ms)

with patch:
madvise(MADV_PAGEOUT) took 26676625 ns (26.677 ms)


[1] https://lore.kernel.org/all/20250513084620.58231-1-21cnbao@xxxxxxxxx/

---
Based on mm-unstable bb420884e9e0. mm-selftests pass.

Dev Jain (9):
  mm/rmap: make nr_pages signed in try_to_unmap_one
  mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one
  mm/rmap: refactor lazyfree unmap commit path to
    commit_ttu_lazyfree_folio()
  mm/memory: Batch set uffd-wp markers during zapping
  mm/rmap: batch unmap folios belonging to uffd-wp VMAs
  mm/swapfile: Make folio_dup_swap batchable
  mm/swapfile: Make folio_put_swap batchable
  mm/rmap: introduce folio_try_share_anon_rmap_ptes
  mm/rmap: enable batch unmapping of anonymous folios

 include/linux/mm_inline.h  |  37 +++--
 include/linux/page-flags.h |  11 ++
 include/linux/rmap.h       |  38 ++++-
 mm/internal.h              |  26 ++++
 mm/memory.c                |  26 +---
 mm/mprotect.c              |  17 ---
 mm/rmap.c                  | 274 ++++++++++++++++++++++++-------------
 mm/shmem.c                 |   8 +-
 mm/swap.h                  |  10 +-
 mm/swapfile.c              |  25 ++--
 10 files changed, 298 insertions(+), 174 deletions(-)

-- 
2.34.1