mm: support batched unmap for lazyfree large folios during reclamation

Currently, the PTEs and rmap of a large folio are removed one at a time.
This is not only slow but also causes the large folio to be unnecessarily
added to deferred_split, which can lead to races between the
deferred_split shrinker callback and memory reclamation. This patch
releases all PTEs and rmap entries in a batch. Currently, it only handles
lazyfree large folios.

The below microbench tries to reclaim 128MB lazyfree large folios
whose sizes are 64KiB:

#include <stdio.h>
#include <sys/mman.h>
#include <string.h>
#include <time.h>

#define SIZE 128*1024*1024 // 128 MB

unsigned long read_split_deferred()
{
FILE *file = fopen("/sys/kernel/mm/transparent_hugepage"
"/hugepages-64kB/stats/split_deferred", "r");
if (!file) {
perror("Error opening file");
return 0;
}

unsigned long value;
if (fscanf(file, "%lu", &value) != 1) {
perror("Error reading value");
fclose(file);
return 0;
}

fclose(file);
return value;
}

int main(int argc, char *argv[])
{
while(1) {
volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

memset((void *)p, 1, SIZE);

madvise((void *)p, SIZE, MADV_FREE);

clock_t start_time = clock();
unsigned long start_split = read_split_deferred();
madvise((void *)p, SIZE, MADV_PAGEOUT);
clock_t end_time = clock();
unsigned long end_split = read_split_deferred();

double elapsed_time = (double)(end_time - start_time) / CLOCKS_PER_SEC;
printf("Time taken by reclamation: %f seconds, split_deferred: %ld\n",
elapsed_time, end_split - start_split);

munmap((void *)p, SIZE);
}
return 0;
}

w/o patch:
~ # ./a.out
Time taken by reclamation: 0.177418 seconds, split_deferred: 2048
Time taken by reclamation: 0.178348 seconds, split_deferred: 2048
Time taken by reclamation: 0.174525 seconds, split_deferred: 2048
Time taken by reclamation: 0.171620 seconds, split_deferred: 2048
Time taken by reclamation: 0.172241 seconds, split_deferred: 2048
Time taken by reclamation: 0.174003 seconds, split_deferred: 2048
Time taken by reclamation: 0.171058 seconds, split_deferred: 2048
Time taken by reclamation: 0.171993 seconds, split_deferred: 2048
Time taken by reclamation: 0.169829 seconds, split_deferred: 2048
Time taken by reclamation: 0.172895 seconds, split_deferred: 2048
Time taken by reclamation: 0.176063 seconds, split_deferred: 2048
Time taken by reclamation: 0.172568 seconds, split_deferred: 2048
Time taken by reclamation: 0.171185 seconds, split_deferred: 2048
Time taken by reclamation: 0.170632 seconds, split_deferred: 2048
Time taken by reclamation: 0.170208 seconds, split_deferred: 2048
Time taken by reclamation: 0.174192 seconds, split_deferred: 2048
...

w/ patch:
~ # ./a.out
Time taken by reclamation: 0.074231 seconds, split_deferred: 0
Time taken by reclamation: 0.071026 seconds, split_deferred: 0
Time taken by reclamation: 0.072029 seconds, split_deferred: 0
Time taken by reclamation: 0.071873 seconds, split_deferred: 0
Time taken by reclamation: 0.073573 seconds, split_deferred: 0
Time taken by reclamation: 0.071906 seconds, split_deferred: 0
Time taken by reclamation: 0.073604 seconds, split_deferred: 0
Time taken by reclamation: 0.075903 seconds, split_deferred: 0
Time taken by reclamation: 0.073191 seconds, split_deferred: 0
Time taken by reclamation: 0.071228 seconds, split_deferred: 0
Time taken by reclamation: 0.071391 seconds, split_deferred: 0
Time taken by reclamation: 0.071468 seconds, split_deferred: 0
Time taken by reclamation: 0.071896 seconds, split_deferred: 0
Time taken by reclamation: 0.072508 seconds, split_deferred: 0
Time taken by reclamation: 0.071884 seconds, split_deferred: 0
Time taken by reclamation: 0.072433 seconds, split_deferred: 0
Time taken by reclamation: 0.071939 seconds, split_deferred: 0
...

Link: https://lkml.kernel.org/r/20250214093015.51024-4-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chis Li <chrisl@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mauricio Faria de Oliveira <mfo@canonical.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shaoqin Huang <shahuang@redhat.com>
Cc: Tangquan Zheng <zhengtangquan@oppo.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yicong Yang <yangyicong@hisilicon.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>