Thanks! On Thu, Jan 25, 2024 at 8:44 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > 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 >
