Re: [PATCH v2] selftests/mm: khugepaged: initialize file contents via mmap

David Hildenbrand (Arm)
2026-04-28T10:06:23Z

On 4/28/26 11:52, Vineet Agarwal wrote:
> ftruncate() is needed before mmap(), since the file is created with
> O_TRUNC and initially has size 0. Without resizing it first, mapping
> and accessing the full range can go beyond EOF.

Ah, that makes sense, worth spelling it out. Indeed, we otherwise get

$ sudo ./khugepaged madvise:file .
Save THP and khugepaged settings... OK
Allocate huge page on fault... OK
Split huge PMD on MADV_DONTNEED... OK

Run test: collapse_full (madvise:file)
Creating ./collapse_test_file for collapse...Bus error

--
Cheers,

David