It allows an application to signal that it no longer needs the data in
the given address range and the underlying pages can be discarded and
reused elsewhere. This is finer grained than working with full areas
or mappings at a time and enables unmapping sections of partially used
mappings without giving up its address space.
Compared with punching holes into a mapping by "mapping over" with
PROT_NONE and MAP_NORESERVE, this has the obvious advantage of not
producing a lot of unused extra areas and saves the corresponding
resources. It is also a lot "lighter" of an operation than cutting
existing areas.
This introduces madvise() alongside the existing posix_madvise() to
allow for OS specific extensions. The constants for both functions are
aliased, the POSIX_MADV_* being a subset of the MADV_* ones without the
non-POSIX extensions. Internally posix_madvise() simply calls madvise().
MADV_FREE is commonly supported in other OSes with various subtle
semantic differences as to when pages are actually freed/cleared and how
or whether the pages are counted against the memory use of a process.
In the variant implemented here, pages are always immediately discarded
and memory counting is not altered. This behaviour should be considered
an implementation detail and may be altered later. The actual unmap and
discard could for example be delayed until pages are needed elsewhere to
reduce overhead in case of repeated discarding and remapping.
Note that MADV_FREE doesn't really align with the rest of the madvise()
API as it works like a command (i.e. discard these pages) and does not
add an attribute to the pages in the given range (i.e. mark these pages
for quick access from now on). As such, an MADV_FREE does not need to be
undone by setting a different advice later on, unlike how the other
flags work. This discrepancy may be the reason why it is not part of
POSIX.
Change-Id: Icc093379125a43e465dc4409d8f5ae0f64e107e0
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2844
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
This reverts hrev54120 and instead adds the commonly supported
MAP_NORESERVE flag to request overcommit.
Using PROT_NONE for overcommit is problematic as the protection of
individual pages can still be changed via mprotect to make them
accessible, but that won't change the commitment. An application
using such a pattern may then unexpectedly run into out of memory
conditions on random writes into the address space.
With MAP_NORESERVE the overcommit can explicitly be requested by
applications that want to reserve address space without producing
memory pressure.
Change-Id: Id213d2245c5e23103e8e0857f7902e0cd8a2c65d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2611
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>
Cleaned up some header style violations, making sure there are two blank lines after the header guards.
This fixes the posix header part of #2191.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@39288 a95241bf-73f2-0310-859d-f6bbb57e9c96
specifying the protection of each page (4 bits per page).
* Added no-op implementation of posix_madvise().
* Replaced a few "addr_t size" parameters by "size_t size".
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@26871 a95241bf-73f2-0310-859d-f6bbb57e9c96
vm_page_write_modified_pages(), save that it only writes pages in the
given range.
* Added vm_page_schedule_write_page_range() which schedules all modified
pages in the given cache's range for writing by the page writer.
* Added _kern_sync_memory() syscall and the msync() POSIX function.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25620 a95241bf-73f2-0310-859d-f6bbb57e9c96
Replaced single-line comments by multi-line comments for ANSI C
compliance.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25433 a95241bf-73f2-0310-859d-f6bbb57e9c96
simply created as files in /boot/var/shared_memory/. The Bootscript
clears the directory.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25374 a95241bf-73f2-0310-859d-f6bbb57e9c96
and defines the macros needed by them.
* Renamed syscall sys_vm_map_file() to _kern_map_file() and changed the
path to an FD parameter. Changed vm_map_file() accordingly and
adjusted the kernel ELF loader and the runtime loader.
* Added syscall _kern_unmap_memory().
* Added bool unmapAddressRange parameter to vm_create_anonymous_area()
and map_backing_store(). If true and the address specification is
B_EXACT_ADDRESS, all areas in the specified address range will be
deleted (unless an area is covered only partially).
* Introduced B_SHARED_AREA flag, which is set on areas that have been
created by {vm,_user}_map_file() with REGION_NO_PRIVATE_MAP. When
fork()ing those areas won't be copied CoW, but rather be cloned. This
is needed for mmap() MAP_SHARED.
* {vm,_user}_map_file() also accept an FD argument < 0, in which case an
anonymous area is created.
* Implemented mmap() and munmap(). Currently there's the restriction
that we can't partially unmap areas. Otherwise the functions should be
rather compliant. We also support the non-POSIX extension
MAP_ANONYMOUS.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@24964 a95241bf-73f2-0310-859d-f6bbb57e9c96
