Lines Matching +full:in +full:- +full:memory
2 No-MMU memory mapping support
5 The kernel has limited support for memory mapping under no-MMU conditions, such
6 as are used in uClinux environments. From the userspace point of view, memory
7 mapping is made use of in conjunction with the mmap() system call, the shmat()
12 Memory mapping behaviour also involves the way fork(), vfork(), clone() and
16 The behaviour is similar between the MMU and no-MMU cases, but not identical;
17 and it's also much more restricted in the latter case:
21 In the MMU case: VM regions backed by arbitrary pages; copy-on-write
24 In the no-MMU case: VM regions backed by arbitrary contiguous runs of
30 shared across fork() or clone() without CLONE_VM in the MMU case. Since
31 the no-MMU case doesn't support these, behaviour is identical to
36 In the MMU case: VM regions backed by pages read from file; changes to
37 the underlying file are reflected in the mapping; copied across fork.
39 In the no-MMU case:
41 - If one exists, the kernel will re-use an existing mapping to the
45 - If possible, the file mapping will be directly on the backing device
50 - If the backing device can't or won't permit direct sharing,
53 memory and any extraneous space beyond the EOF will be cleared
55 - Writes to the file do not affect the mapping; writes to the mapping
56 are visible in other processes (no MMU protection), but should not
61 In the MMU case: like the non-PROT_WRITE case, except that the pages in
66 In the no-MMU case: works much like the non-PROT_WRITE case, except
71 In the MMU case: VM regions backed by pages read from file; changes to
75 In the no-MMU case: not supported.
77 (#) Memory backed regular file, MAP_SHARED, PROT_READ / PROT_EXEC / PROT_WRITE
79 In the MMU case: As for ordinary regular files.
81 In the no-MMU case: The filesystem providing the memory-backed file
83 sequence by providing a contiguous sequence of pages to map. In that
84 case, a shared-writable memory mapping will be possible. It will work
88 (#) Memory backed blockdev, MAP_SHARED, PROT_READ / PROT_EXEC / PROT_WRITE
90 In the MMU case: As for ordinary regular files.
92 In the no-MMU case: As for memory backed regular files, but the
95 all its memory as a contiguous array upfront.
97 (#) Memory backed chardev, MAP_SHARED, PROT_READ / PROT_EXEC / PROT_WRITE
99 In the MMU case: As for ordinary regular files.
101 In the no-MMU case: The character device driver may choose to honour
103 provides memory or quasi-memory that can be accessed directly. Examples
108 Further notes on no-MMU MMAP
112 page-aligned. This is because XIP may take place, and the data may not be
113 paged aligned in the backing store.
117 of the space may be wasted as the kernel must allocate a power-of-2
121 (#) The memory allocated by a request for an anonymous mapping will normally
122 be cleared by the kernel before being returned in accordance with the
125 In the MMU case this can be achieved with reasonable performance as
130 initialize the contents of a page - depending on the write-usage of the
133 In the no-MMU case, however, anonymous mappings are backed by physical
138 However, for memory that isn't required to be precleared - such as that
139 returned by malloc() - mmap() can take a MAP_UNINITIALIZED flag to
140 indicate to the kernel that it shouldn't bother clearing the memory before
144 uClibc uses this to speed up malloc(), and the ELF-FDPIC binfmt uses this
148 visible through /proc/maps in no-MMU mode.
150 (#) A list of all the mappings in use by a process is visible through
151 /proc/<pid>/maps in no-MMU mode.
154 result in an error.
157 driver or filesystem so that the contents can be read into the memory
163 Interprocess shared memory
166 Both SYSV IPC SHM shared memory and POSIX shared memory is supported in NOMMU
174 Futexes are supported in NOMMU mode if the arch supports them. An error will
176 mappings made by a process or if the mapping in which the address lies does not
180 No-MMU mremap
186 memory to which the mapping refers, or if a smaller slab object could be used.
195 a previously mapped object. It may not be used to create holes in existing
206 file->f_op->get_unmapped_area() operation. The mmap() routines will call this
216 The file->f_op->mmap() operation will be called to actually inaugurate the
220 The vm_ops->close() routine will be invoked when the last mapping on a chardev
224 It is permitted also for the file->f_op->get_unmapped_area() operation to
225 return -ENOSYS. This will be taken to mean that this operation just doesn't
229 direct the call to the device-specific driver. Under such circumstances, the
236 looking at them in certain modes. Flash chips can be like this; for
237 instance if they're in programming or erase mode, you might see the
238 status reflected in the mapping, instead of the data.
240 In such a case, care must be taken lest userspace see a shared or a
247 Providing shareable memory-backed file support
250 Provision of shared mappings on memory backed files is similar to the provision
258 memory.
260 Memory backed devices are indicated by the mapping's backing device info having
269 should allocate sufficient contiguous memory to honour any supported mapping.
275 NOMMU mmap automatically rounds up to the nearest power-of-2 number of pages
276 when performing an allocation. This can have adverse effects on memory
278 aggressively trim allocations and discard any excess pages back in to the page
279 allocator. In order to retain finer-grained control over fragmentation, this