CODEWITHSUNDEEP
linuxmemory-management
Infinite
Infinite

Reputation: 3408

mprotect(addr, size, PROT_NONE) for guard pages and its memory consumption

I allocated some memory using memalign, and I set the last page as a guard page using mprotec(adde, size, PROT_NONE), so this page is inaccessible.

Does the inaccessible page consume physical memory? In my opinion, the kernel can offline the physical pages safely, right?

I also tried madvise(MADV_SOFT_OFFLINE) to manually offline the physical memory but the function always fails.

Can anybody tell me the internal behavior of kernel with mprotect(PROT_NONE), and how to offline the physical memory to save physical memory consumption?

Upvotes: 3

Views: 1572

Answers (1)

Basile Starynkevitch
Basile Starynkevitch

Reputation: 1

Linux applications are using virtual memory. Only the kernel is managing physical RAM. Application code don't see the physical RAM.

A segment protected with mprotect & PROT_NONE won't consume any RAM.

You should allocate your segment with mmap(2) (maybe you want MAP_NORESERVE). Mixing memalign with mprotect may probably break libc invariants.

Read carefully madvise(2) man page. MADV_SOFT_OFFLINE may require a specially configured kernel.

Upvotes: 2

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