Comments (3)
From the man page
MAP_LOCKED (since Linux 2.5.37)
Mark the mapped region to be locked in the same way as mlock(2). This implementation will try to populate (prefault) the whole range but the mmap() call doesn't fail with ENOMEM if this fails. Therefore major faults might happen later on. So the
semantic is not as strong as mlock(2). One should use mmap() plus mlock(2) when major faults are not acceptable after the initialization of the mapping. The MAP_LOCKED flag is ignored in older kernels.
Since it can fail silently, maybe it would be better to provide only lock
and unlock
methods and ignore the flag?
Otherwise, it should be handled just like MAP_POPULATE
IMHO.
What I wondered about in the initial PR is whether can have at least some tests for the lock/unlock functionality. What is resource limit for locking memory in GitHub actions? Would that be sufficient for a small test case?
from memmap2-rs.
Since it can fail silently, maybe it would be better to provide only
lock
andunlock
methods and ignore the flag?
That sounds like a good idea.
Do I understand the mmap documentation correctly, that if I would want to have a similar to the MAP_LOCKED
flag, I'd call populate()
and the mlock()
? That should work for my use case (populate()
wasn't a thing at the time of the fork).
So I'll do a PR with lock()
and unlock()
only (I guess the names should be without the leading "m", just as advise()
).
I wanted to do a test, but I couldn't think of a way to do it. How would I test that a page is actually locked? Did you think of creating a lock of a mmap that is bigger than the available memory which then should fail as it won't swap?
from memmap2-rs.
Do I understand the mmap documentation correctly, that if I would want to have a similar to the MAP_LOCKED flag, I'd call populate() and the mlock()? That should work for my use case (populate() wasn't a thing at the time of the fork).
From the man page
mlock(), mlock2(), and munlock()
mlock() locks pages in the address range starting at addr and continuing for len bytes. All pages that contain a part of the specified address range are guaranteed to be resident in RAM when the call returns successfully; the pages are guaranteed to stay
in RAM until later unlocked.
I would assume that MAP_POPULATE
is not even necessary.
I wanted to do a test, but I couldn't think of a way to do it. How would I test that a page is actually locked? Did you think of creating a lock of a mmap that is bigger than the available memory which then should fail as it won't swap?
I was thinking about having the test make the system calls without errors would be helpful already. Theoretically /proc/self/smaps
could be checked to determine if the range is locked into memory, but I think that might be a bit too much (and too specific to Linux).
from memmap2-rs.
Related Issues (20)
- Migrate to `safer_owning_ref` HOT 1
- why does memmap2::Mmap::map need to be unsafe? HOT 4
- Implement AsRawFd, IntoRawFd, AsRawHandle, IntoRawHandle and Into<Stdio> for MMap HOT 2
- Composite memory maps currently impossible HOT 7
- mmap'd anon pages fail in io_uring IOSQE_BUFFER_SELECT usage HOT 2
- advise_writes_unsafely_to_part_of_map test fails on powerpc64le-unknown-linux-gnu HOT 2
- error[E0433]: failed to resolve: could not find `Advice` in `memmap2` HOT 1
- PermissionDenied, message: "Access is denied." at remove file after read on Github Action WIndows HOT 2
- Doesn't compile for freebsd HOT 3
- v0.9.2 build failed for android target. HOT 3
- Support for `MS_INVALIDATE`? HOT 8
- Mac osx support HOT 1
- Support `mremap(2)` HOT 1
- Mapping beyond 4GB offset if broken on 32 bit glibc (Linux) HOT 3
- Support multiple advice HOT 2
- Contributing a migration from rustix to libc HOT 9
- MSRV and edition HOT 5
- Merging changes with memmapix HOT 24
- memmap2 `advise` is unsound HOT 8
- Interest is supporting mbind HOT 10
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from memmap2-rs.