Re: [PATCH 1/3] mm: add functions folio_in_range() and folio_within_vma()

Yin Fengwei
2023-08-03T01:38:29Z

On 8/2/23 23:12, Ryan Roberts wrote:
>>> I also wonder if you should change the name of folio_within_vma() to something
>>> like folio_test_cont_in_vma() to disambiguate from the case where the folio may
>>> be fully mapped with a discontiguity (although perhaps that's not possible
>>> because a mremap would result in distinct vmas... would a new mmap in the hole
>>> cause a merge of all 3?).
>> I don't think it's possible as mremap reuse original pgoff of VMA to new VMA. I suppose
>> it will prevent VMA merging. But I didn't check detail.
>
> pgoff is not relevant for anon though, right?
anonymous folio->index is related with vma->vm_pgoff.

>
> FWIW, I wrote a test to check if merging is performed. Interestingly, v5.4 (on x86) *does* merge the VMAs in this case, but v6.5-rc3 (on arm64) *does not* merge the VMAs in this case.
What if you fault in the pages to the mapped VMAs?

>
> I think you should assume it might be possible in some cases.
I don't think mremap target VMA could be merged with prev/next
unless it's merged back (move the pieces large folio together).

Regards
Yin, Fengwei

>
>
> #define _GNU_SOURCE
> #include <stdlib.h>
> #include <stdio.h>
> #include <sys/mman.h>
> #include <unistd.h>
>
> int main(int argc, char **argv)
> {
> size_t pgsize = getpagesize();
> char *memarea;
> char *memlow;
> char *memmid;
> char *memhigh;
> int ret = 0;
>
> // Get a free vm area big enough for 5 pages.
> memarea = mmap(NULL, pgsize * 5,
> PROT_NONE,
> MAP_PRIVATE | MAP_ANONYMOUS,
> -1, 0);
> if (memarea == MAP_FAILED) {
> perror("mmap 1");
> exit(1);
> }
>
> // Map 2 pages one page into allocated area.
> memlow = mmap(memarea + pgsize, pgsize * 2,
> PROT_READ | PROT_WRITE,
> MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
> -1, 0);
> if (memlow == MAP_FAILED) {
> perror("mmap 2");
> exit(1);
> }
>
> // Move the second allocated page one page higher.
> memhigh = mremap(memarea + pgsize * 2, pgsize, pgsize,
> MREMAP_FIXED | MREMAP_MAYMOVE,
> memarea + pgsize * 3);
> if (memhigh == MAP_FAILED) {
> perror("mremap");
> exit(1);
> }
>
> // We should now have:
> // | page 0 | page 1 | page 2 | page 3 | page 4 |
> // | NONE | vma 1 | empty | vma 2 | NONE |
> printf("Check for 2 vmas with hole: pid=%d, memarea=%p, memlow=%p, memhigh=%p\n",
> getpid(), memarea, memlow, memhigh);
> getchar();
>
> // Now map a page in the empty space.
> memmid = mmap(memarea + pgsize * 2, pgsize,
> PROT_READ | PROT_WRITE,
> MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
> -1, 0);
> if (memmid == MAP_FAILED) {
> perror("mmap 2");
> exit(1);
> }
>
> // We should now have:
> // | page 0 | page 1 | page 2 | page 3 | page 4 |
> // | NONE | vma 1 | NONE |
> printf("Check for single merged vma: pid=%d, memarea=%p, memlow=%p, memmid=%p, memhigh=%p\n",
> getpid(), memarea, memlow, memmid, memhigh);
> getchar();
>
> return ret;
> }
>
>
>
> Output on v5.4:
>
> Check for 2 vmas with hole: pid=171038, memarea=0x7fe6c34d9000, memlow=0x7fe6c34da000, memhigh=0x7fe6c34dc000
> Check for single merged vma: pid=171038, memarea=0x7fe6c34d9000, memlow=0x7fe6c34da000, memmid=0x7fe6c34db000, memhigh=0x7fe6c34dc000
>
> And maps output at the 2 check points:
>
> (base) ryarob01@e125769:/data_nvme0n1/ryarob01/granule_perf$ cat /proc/171038/maps
> 55e55c258000-55e55c259000 r--p 00000000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c259000-55e55c25a000 r-xp 00001000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c25a000-55e55c25b000 r--p 00002000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c25b000-55e55c25c000 r--p 00002000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c25c000-55e55c25d000 rw-p 00003000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c403000-55e55c424000 rw-p 00000000 00:00 0 [heap]
> 7fe6c32d2000-7fe6c32f4000 r--p 00000000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c32f4000-7fe6c346c000 r-xp 00022000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c346c000-7fe6c34ba000 r--p 0019a000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c34ba000-7fe6c34be000 r--p 001e7000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c34be000-7fe6c34c0000 rw-p 001eb000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c34c0000-7fe6c34c6000 rw-p 00000000 00:00 0
> 7fe6c34d9000-7fe6c34da000 ---p 00000000 00:00 0
> 7fe6c34da000-7fe6c34db000 rw-p 00000000 00:00 0
> 7fe6c34dc000-7fe6c34dd000 rw-p 00000000 00:00 0
> 7fe6c34dd000-7fe6c34de000 ---p 00000000 00:00 0
> 7fe6c34de000-7fe6c34df000 r--p 00000000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c34df000-7fe6c3502000 r-xp 00001000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c3502000-7fe6c350a000 r--p 00024000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c350b000-7fe6c350c000 r--p 0002c000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c350c000-7fe6c350d000 rw-p 0002d000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c350d000-7fe6c350e000 rw-p 00000000 00:00 0
> 7fff39a11000-7fff39a32000 rw-p 00000000 00:00 0 [stack]
> 7fff39a83000-7fff39a86000 r--p 00000000 00:00 0 [vvar]
> 7fff39a86000-7fff39a87000 r-xp 00000000 00:00 0 [vdso]
> ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall]
> (base) ryarob01@e125769:/data_nvme0n1/ryarob01/granule_perf$ cat /proc/171038/maps
> 55e55c258000-55e55c259000 r--p 00000000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c259000-55e55c25a000 r-xp 00001000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c25a000-55e55c25b000 r--p 00002000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c25b000-55e55c25c000 r--p 00002000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c25c000-55e55c25d000 rw-p 00003000 fd:00 5297466 /data_nvme0n1/ryarob01/granule_perf/merge
> 55e55c403000-55e55c424000 rw-p 00000000 00:00 0 [heap]
> 7fe6c32d2000-7fe6c32f4000 r--p 00000000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c32f4000-7fe6c346c000 r-xp 00022000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c346c000-7fe6c34ba000 r--p 0019a000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c34ba000-7fe6c34be000 r--p 001e7000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c34be000-7fe6c34c0000 rw-p 001eb000 fd:02 9573653 /lib/x86_64-linux-gnu/libc-2.31.so
> 7fe6c34c0000-7fe6c34c6000 rw-p 00000000 00:00 0
> 7fe6c34d9000-7fe6c34da000 ---p 00000000 00:00 0
> 7fe6c34da000-7fe6c34dd000 rw-p 00000000 00:00 0
> 7fe6c34dd000-7fe6c34de000 ---p 00000000 00:00 0
> 7fe6c34de000-7fe6c34df000 r--p 00000000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c34df000-7fe6c3502000 r-xp 00001000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c3502000-7fe6c350a000 r--p 00024000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c350b000-7fe6c350c000 r--p 0002c000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c350c000-7fe6c350d000 rw-p 0002d000 fd:02 9573649 /lib/x86_64-linux-gnu/ld-2.31.so
> 7fe6c350d000-7fe6c350e000 rw-p 00000000 00:00 0
> 7fff39a11000-7fff39a32000 rw-p 00000000 00:00 0 [stack]
> 7fff39a83000-7fff39a86000 r--p 00000000 00:00 0 [vvar]
> 7fff39a86000-7fff39a87000 r-xp 00000000 00:00 0 [vdso]
> ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall]
>
>
> Output on v6.5-rc3:
>
> Check for 2 vmas with hole: pid=3181, memarea=0xfffff7ff2000, memlow=0xfffff7ff3000, memhigh=0xfffff7ff5000
> Check for single merged vma: pid=3181, memarea=0xfffff7ff2000, memlow=0xfffff7ff3000, memmid=0xfffff7ff4000, memhigh=0xfffff7ff5000
>
> And maps output at the 2 check points:
>
> ubuntu@ubuntuvm:~/linux$ cat /proc/3181/maps
> aaaaaaaa0000-aaaaaaaa1000 r-xp 00000000 fe:02 8199010 /home/ubuntu/merge
> aaaaaaab0000-aaaaaaab1000 r--p 00000000 fe:02 8199010 /home/ubuntu/merge
> aaaaaaab1000-aaaaaaab2000 rw-p 00001000 fe:02 8199010 /home/ubuntu/merge
> aaaaaaab2000-aaaaaaad3000 rw-p 00000000 00:00 0 [heap]
> fffff7e00000-fffff7f89000 r-xp 00000000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f89000-fffff7f98000 ---p 00189000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f98000-fffff7f9c000 r--p 00188000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f9c000-fffff7f9e000 rw-p 0018c000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f9e000-fffff7faa000 rw-p 00000000 00:00 0
> fffff7fc2000-fffff7fed000 r-xp 00000000 fe:02 41316494 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1
> fffff7ff2000-fffff7ff3000 ---p 00000000 00:00 0
> fffff7ff3000-fffff7ff4000 rw-p 00000000 00:00 0
> fffff7ff5000-fffff7ff6000 rw-p 00000000 00:00 0
> fffff7ff6000-fffff7ff7000 ---p 00000000 00:00 0
> fffff7ff7000-fffff7ff9000 rw-p 00000000 00:00 0
> fffff7ff9000-fffff7ffb000 r--p 00000000 00:00 0 [vvar]
> fffff7ffb000-fffff7ffc000 r-xp 00000000 00:00 0 [vdso]
> fffff7ffc000-fffff7ffe000 r--p 0002a000 fe:02 41316494 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1
> fffff7ffe000-fffff8000000 rw-p 0002c000 fe:02 41316494 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1
> fffffffdf000-1000000000000 rw-p 00000000 00:00 0 [stack]
> ubuntu@ubuntuvm:~/linux$ cat /proc/3181/maps
> aaaaaaaa0000-aaaaaaaa1000 r-xp 00000000 fe:02 8199010 /home/ubuntu/merge
> aaaaaaab0000-aaaaaaab1000 r--p 00000000 fe:02 8199010 /home/ubuntu/merge
> aaaaaaab1000-aaaaaaab2000 rw-p 00001000 fe:02 8199010 /home/ubuntu/merge
> aaaaaaab2000-aaaaaaad3000 rw-p 00000000 00:00 0 [heap]
> fffff7e00000-fffff7f89000 r-xp 00000000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f89000-fffff7f98000 ---p 00189000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f98000-fffff7f9c000 r--p 00188000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f9c000-fffff7f9e000 rw-p 0018c000 fe:02 41410085 /usr/lib/aarch64-linux-gnu/libc.so.6
> fffff7f9e000-fffff7faa000 rw-p 00000000 00:00 0
> fffff7fc2000-fffff7fed000 r-xp 00000000 fe:02 41316494 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1
> fffff7ff2000-fffff7ff3000 ---p 00000000 00:00 0
> fffff7ff3000-fffff7ff4000 rw-p 00000000 00:00 0
> fffff7ff4000-fffff7ff5000 rw-p 00000000 00:00 0
> fffff7ff5000-fffff7ff6000 rw-p 00000000 00:00 0
> fffff7ff6000-fffff7ff7000 ---p 00000000 00:00 0
> fffff7ff7000-fffff7ff9000 rw-p 00000000 00:00 0
> fffff7ff9000-fffff7ffb000 r--p 00000000 00:00 0 [vvar]
> fffff7ffb000-fffff7ffc000 r-xp 00000000 00:00 0 [vdso]
> fffff7ffc000-fffff7ffe000 r--p 0002a000 fe:02 41316494 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1
> fffff7ffe000-fffff8000000 rw-p 0002c000 fe:02 41316494 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1
> fffffffdf000-1000000000000 rw-p 00000000 00:00 0 [stack]