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And in order to help all readers > and reviewers to > > reproduce this bug, share a reproducer here: I reproduced this problem under a VM this way: $ sudo ./stress-ng --swap 1 // on another terminal $ for i in `seq 8`; do ./swap & done Looks simpler than yours :-) (Didn't realize you have posted your reproducer here since I'm not CCed and just found it after invented mine) Then the warning message normally appear within a few seconds. Here is the code for the above swap prog: #include #include #include #define SIZE 0x100000 int main(void) { int i, ret; void *p; p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0); if (p == MAP_FAILED) { perror("mmap"); return -1; } ret = 0; while (1) { for (i = 0; i < SIZE; i += 0x1000) ((char *)p)[i] = 1; ret = madvise(p, SIZE, MADV_PAGEOUT); if (ret != 0) { perror("madvise"); break; } } return ret; } Unfortunately, this test prog did not work on kernels before v5.4 because MADV_PAGEOUT is introduced in v5.4. I tested on v5.4 and the problem is also there. Haven't found a way to trigger swap with swap device come and go on kernels before v5.4; tried putting the test prog in a memcg with memory limit but then the prog is easily killed due to nowhere to swap out. > > swap_bomb.sh > > #!/usr/bin/env bash > > stress-ng -a 1 --class vm -t 12h --metrics --times -x bigheap,stackmmap,mlock,vm-splice,mmapaddr,mmapfixed,mmapfork,mmaphuge,mmapmany,mprotect,mremap,msync,msyncmany,physpage,tmpfs,vm-addr,vm-rw,brk,vm-segv,userfaultfd,malloc,stack,munmap,dev-shm,bad-altstack,shm-sysv,pageswap,madvise,vm,shm,env,mmap > --verify -v & > stress-ng -a 1 --class vm -t 12h --metrics --times -x bigheap,stackmmap,mlock,vm-splice,mmapaddr,mmapfixed,mmapfork,mmaphuge,mmapmany,mprotect,mremap,msync,msyncmany,physpage,tmpfs,vm-addr,vm-rw,brk,vm-segv,userfaultfd,malloc,stack,munmap,dev-shm,bad-altstack,shm-sysv,pageswap,madvise,vm,shm,env,mmap > --verify -v & > stress-ng -a 1 --class vm -t 12h --metrics --times -x bigheap,stackmmap,mlock,vm-splice,mmapaddr,mmapfixed,mmapfork,mmaphuge,mmapmany,mprotect,mremap,msync,msyncmany,physpage,tmpfs,vm-addr,vm-rw,brk,vm-segv,userfaultfd,malloc,stack,munmap,dev-shm,bad-altstack,shm-sysv,pageswap,madvise,vm,shm,env,mmap > --verify -v & > stress-ng -a 1 --class vm -t 12h --metrics --times -x bigheap,stackmmap,mlock,vm-splice,mmapaddr,mmapfixed,mmapfork,mmaphuge,mmapmany,mprotect,mremap,msync,msyncmany,physpage,tmpfs,vm-addr,vm-rw,brk,vm-segv,userfaultfd,malloc,stack,munmap,dev-shm,bad-altstack,shm-sysv,pageswap,madvise,vm,shm,env,mmap > --verify -v > > > madvise_shared.c > > #include > #include > #include > #include > > #define MSIZE (1024 * 1024 * 2) > > int main() > { >         char *shm_addr; >         unsigned long i; > >         while (1) { >                 // Map shared memory segment >                 shm_addr = >                     mmap(NULL, MSIZE, PROT_READ | PROT_WRITE, >                          MAP_SHARED | MAP_ANONYMOUS, -1, 0); >                 if (shm_addr == MAP_FAILED) { >                         perror("Failed to map shared memory segment"); >                         exit(EXIT_FAILURE); >                 } > >                 for (i = 0; i < MSIZE; i++) { >                         shm_addr[i] = 1; >                 } > >                 // Advise kernel on usage pattern of shared memory >                 if (madvise(shm_addr, MSIZE, MADV_PAGEOUT) == -1) { >                         perror >                             ("Failed to advise kernel on shared memory > usage"); >                         exit(EXIT_FAILURE); >                 } > >                 for (i = 0; i < MSIZE; i++) { >                         shm_addr[i] = 1; >                 } > >                 // Advise kernel on usage pattern of shared memory >                 if (madvise(shm_addr, MSIZE, MADV_PAGEOUT) == -1) { >                         perror >                             ("Failed to advise kernel on shared memory > usage"); >                         exit(EXIT_FAILURE); >                 } >                 // Use shared memory >                 printf("Hello, shared memory: 0x%lx\n", shm_addr); > >                 // Unmap shared memory segment >                 if (munmap(shm_addr, MSIZE) == -1) { >                         perror("Failed to unmap shared memory segment"); >                         exit(EXIT_FAILURE); >                 } >         } > >         return 0; > } > > The bug will reproduce more quickly (about 2~5 minutes) if concurrent more > swap_bomb.sh and madvise_shared. > > Thanks.