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

[Dev Jain]

On 10/03/26 6:29 pm, Lance Yang wrote:
> 
> On Tue, Mar 10, 2026 at 01:00:04PM +0530, Dev Jain wrote:
>> 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)
> 
> Good numbers! Just tested on x86 KVM with THP=never, no performance
> regression observed.

Thanks Lance!

Although still I'll try to get no-regression numbers and perf-boost
numbers on x86 myself and post it in next version.

> 
> Cheers,
> Lance
>