Re: [PATCH v3 2/2] mm: attempt to batch free swap entries for zap_pte_range()

[David Hildenbrand <david@redhat.com>]

On 07.08.24 23:58, Barry Song wrote:
> From: Barry Song <v-songbaohua@oppo.com>
> 
> Zhiguo reported that swap release could be a serious bottleneck
> during process exits[1]. With mTHP, we have the opportunity to
> batch free swaps.
> Thanks to the work of Chris and Kairui[2], I was able to achieve
> this optimization with minimal code changes by building on their
> efforts.
> If swap_count is 1, which is likely true as most anon memory are
> private, we can free all contiguous swap slots all together.
> 
> Ran the below test program for measuring the bandwidth of munmap
> using zRAM and 64KiB mTHP:
> 
>   #include <sys/mman.h>
>   #include <sys/time.h>
>   #include <stdlib.h>
> 
>   unsigned long long tv_to_ms(struct timeval tv)
>   {
>          return tv.tv_sec * 1000 + tv.tv_usec / 1000;
>   }
> 
>   main()
>   {
>          struct timeval tv_b, tv_e;
>          int i;
>   #define SIZE 1024*1024*1024
>          void *p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
>                                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>          if (!p) {
>                  perror("fail to get memory");
>                  exit(-1);
>          }
> 
>          madvise(p, SIZE, MADV_HUGEPAGE);
>          memset(p, 0x11, SIZE); /* write to get mem */
> 
>          madvise(p, SIZE, MADV_PAGEOUT);
> 
>          gettimeofday(&tv_b, NULL);
>          munmap(p, SIZE);
>          gettimeofday(&tv_e, NULL);
> 
>          printf("munmap in bandwidth: %ld bytes/ms\n",
>                          SIZE/(tv_to_ms(tv_e) - tv_to_ms(tv_b)));
>   }
> 
> The result is as below (munmap bandwidth):
>                  mm-unstable  mm-unstable-with-patch
>     round1       21053761      63161283
>     round2       21053761      63161283
>     round3       21053761      63161283
>     round4       20648881      67108864
>     round5       20648881      67108864
> 
> munmap bandwidth becomes 3X faster.
> 
> [1] https://lore.kernel.org/linux-mm/20240731133318.527-1-justinjiang@vivo.com/
> [2] https://lore.kernel.org/linux-mm/20240730-swap-allocator-v5-0-cb9c148b9297@kernel.org/
> 
> Cc: Kairui Song <kasong@tencent.com>
> Cc: Chris Li <chrisl@kernel.org>
> Cc: "Huang, Ying" <ying.huang@intel.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Kalesh Singh <kaleshsingh@google.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: David Hildenbrand <david@redhat.com>
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> ---

All looks straight forward to me

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb