On 25.01.24 13:28, Lance Yang wrote:
Hello Everyone, I've noticed that using mprotect(PROT_NONE) with madvise(MADV_DONTNEED) is much faster than mmap(PROT_NONE, MAP_FIXED) alone for changing permissions and zeroing pages. I have maintained a chunk-allocator internally at the company. It allocates a chunk using mmap(PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0), releases a chunk using mmap(PROT_NONE, MAP_ANON|MAP_FIXED|MAP_PRIVATE, -1, 0), and reuses a chunk using mprotect(PROT_READ|PROT_WRITE). Recently, I replaced mmap(PROT_NONE, MAP_FIXED) with mprotect(PROT_NONE) + madvise(MADV_DONTNEED) to reduce the latency of releasing chunks. Test code: https://github.com/ioworker0/mmapvsmprotect/blob/main/test2.c Here are the test results on my machine: CPU: AMD EPYC 7R13 Processor Kernel: 6.2.0 Elapsed Time for mprotect+madvise: 3670 nanoseconds Elapsed Time for mmap: 5520 nanoseconds
mprotect+madvise won't free page tables, mmap will. That's the biggest difference.
-- Cheers, David / dhildenb
