forked from hpc/xpmem
-
Notifications
You must be signed in to change notification settings - Fork 0
/
README
53 lines (41 loc) · 2.48 KB
/
README
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
***************************************************************************
***************************************************************************
***************************************************************************
If you wish to contribute to or want to see the latest version of XPMEM
the new repository is @ http://gitlab.com/hjelmn/xpmem. I do not intent
to continue to use github for this repository.
***************************************************************************
***************************************************************************
***************************************************************************
This is an experimental version of XPMEM based on a version provided by
Cray and uploaded to https://code.google.com/p/xpmem. This version supports
any kernel 3.12 and newer. Keep in mind there may be bugs and this version
may cause kernel panics, code crashes, eat your cat, etc.
XPMEM is a Linux kernel module that enables a process to map the
memory of another process into its virtual address space. Source code
can be obtained by cloning the Git repository, original Mercurial
repository or by downloading a tarball from the link above.
The XPMEM API has three main functions:
xpmem_make()
xpmem_get()
xpmem_attach()
A process calls xpmem_make() to export a region of its virtual address
space. Other processes can then attach to the region by calling
xpmem_get() and xpmem_attach(). After a memory region is attached, it
is accessed via direct loads and stores. This enables upper-level
protocols such as MPI and SHMEM to perform single-copy address-space
to address-space transfers, completely at user-level.
Note, there is a limitation to the usage of an attached region. Any
system call that will call get_user_pages() on the region from the
non-owning process with get EFAULT. This include pthread mutexes
and condition variable, and SYS V semaphores. We intend to address
this limitation in a future release.
XPMEM regions are free to have "holes" in them, meaning virtual memory
regions that are not allocated. This makes XPMEM somewhat more
flexible than mmap(). A process could, for example, export a region
via XPMEM starting at address 0 and extending 4 GB. Accesses to
allocated (valid) virtual addresses in this region proceed normally,
and pages are mapped between address spaces on demand. A segfault will
occur if the source process or any other process mapping the region
tries to access an unallocated (invalid) virtual address in the
region.