Memory Management

Memory Mappings

mmap and munmap

Supported functionality in SCML:

prot = PROT_NONE |
    PROT_EXEC |
    PROT_READ |
    PROT_WRITE;
opt_flags =
    MAP_ANONYMOUS |
    MAP_FIXED |
    MAP_FIXED_NOREPLACE |
    MAP_GROWSDOWN |
    MAP_HUGETLB |
    MAP_LOCKED |
    MAP_NONBLOCK |
    MAP_NORESERVE |
    MAP_POPULATE |
    MAP_SYNC;

// Create a private memory mapping
mmap(
    addr, length,
    prot = <prot>, 
    flags = MAP_PRIVATE | <opt_flags>
    fd, offset
);
    
// Create a shared memory mapping
mmap(
    addr, length,
    prot = <prot>, 
    flags = MAP_SHARED | MAP_SHARED_VALIDATE | <opt_flags>
    fd, offset
);

// Unmap a memory mapping
munmap(addr, length);

Silently-ignored flags:

• MAP_HUGETLB
• MAP_GROWSDOWN
• MAP_LOCKED
• MAP_NONBLOCK
• MAP_NORESERVE
• MAP_POPULATE
• MAP_SYNC

Partially supported flags:

• MAP_FIXED_NOREPLACE is treated as MAP_FIXED

Unsupported flags:

• MAP_32BIT
• MAP_HUGE_1GB
• MAP_HUGE_2MB
• MAP_UNINITIALIZED

For more information, see the man page.

msync

Supported functionality in SCML:

// Flush memory region to disk asynchronously
msync(
    addr, length,
    flags = MS_ASYNC | MS_INVALIDATE
);

// Flush memory region to disk synchronously
msync(
    addr, length,
    flags = MS_SYNC | MS_INVALIDATE
);

Silently-ignored flags:

• MS_INVALIDATE is ignored because all processes use the same page cache

For more information, see the man page.

mremap

Supported functionality in SCML:

// Resize an existing memory mapping. Relocation is allowed if given `MREMAP_MAYMOVE`.
mremap(
    old_address,
    old_size,
    new_size,
    flags = MREMAP_MAYMOVE
);

// Resize an existing memory mapping and force relocation to a specified location.
mremap(
    old_address,
    old_size,
    new_size,
    flags = MREMAP_MAYMOVE | MREMAP_FIXED,
    new_address
);

For more information, see the man page.

mprotect

Supported functionality in SCML:

// Set memory access permissions
mprotect(
    addr,
    len,
    prot = <prot>
);

Silently-ignored protection flags:

• PROT_SEM
• PROT_SAO
• PROT_GROWSUP
• PROT_GROWSDOWN

For more information, see the man page.

madvise

Supported functionality in SCML:

// Apply the default memory access pattern with no special optimizations
madvise(addr, length, advice = MADV_NORMAL);

// Indicate sequential access to enable aggressive read-ahead and immediate page release
madvise(addr, length, advice = MADV_SEQUENTIAL);

// Prefetch pages for near-future access to reduce latency
madvise(addr, length, advice = MADV_WILLNEED);

Silently-ignored advice:

• MADV_DONTNEED

Unsupported advice:

• MADV_RANDOM
• MADV_REMOVE
• MADV_DONTFORK
• MADV_DOFORK
• MADV_HWPOISON
• MADV_MERGEABLE
• MADV_UNMERGEABLE
• MADV_SOFT_OFFLINE
• MADV_HUGEPAGE
• MADV_NOHUGEPAGE
• MADV_DONTDUMP
• MADV_DODUMP
• MADV_FREE
• MADV_WIPEONFORK
• MADV_KEEPONFORK

For more information, see the man page.