начать / остановить свопинг в файл / устройство (start/stop swapping to file/device)
Имя (Name)
swapon, swapoff - start/stop swapping to file/device
Синопсис (Synopsis)
#include <sys/swap.h>
int swapon(const char *path, int swapflags);
int swapoff(const char *path);
Описание (Description)
swapon() sets the swap area to the file or block device specified
by path. swapoff() stops swapping to the file or block device
specified by path.
If the SWAP_FLAG_PREFER flag is specified in the swapon()
swapflags argument, the new swap area will have a higher priority
than default. The priority is encoded within swapflags as:
(prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK
If the SWAP_FLAG_DISCARD flag is specified in the swapon()
swapflags argument, freed swap pages will be discarded before
they are reused, if the swap device supports the discard or trim
operation. (This may improve performance on some Solid State
Devices, but often it does not.) See also NOTES.
These functions may be used only by a privileged process (one
having the CAP_SYS_ADMIN capability).
Priority
Each swap area has a priority, either high or low. The default
priority is low. Within the low-priority areas, newer areas are
even lower priority than older areas.
All priorities set with swapflags are high-priority, higher than
default. They may have any nonnegative value chosen by the
caller. Higher numbers mean higher priority.
Swap pages are allocated from areas in priority order, highest
priority first. For areas with different priorities, a higher-
priority area is exhausted before using a lower-priority area.
If two or more areas have the same priority, and it is the
highest priority available, pages are allocated on a round-robin
basis between them.
As of Linux 1.3.6, the kernel usually follows these rules, but
there are exceptions.
Возвращаемое значение (Return value)
On success, zero is returned. On error, -1 is returned, and
errno is set to indicate the error.
Ошибки (Error)
EBUSY (for swapon()) The specified path is already being used as
a swap area.
EINVAL The file path exists, but refers neither to a regular file
nor to a block device;
EINVAL (swapon()) The indicated path does not contain a valid
swap signature or resides on an in-memory filesystem such
as tmpfs(5).
EINVAL (since Linux 3.4)
(swapon()) An invalid flag value was specified in
swapflags.
EINVAL (swapoff()) path is not currently a swap area.
ENFILE The system-wide limit on the total number of open files
has been reached.
ENOENT The file path does not exist.
ENOMEM The system has insufficient memory to start swapping.
EPERM The caller does not have the CAP_SYS_ADMIN capability.
Alternatively, the maximum number of swap files are
already in use; see NOTES below.
Стандарты (Conforming to)
These functions are Linux-specific and should not be used in
programs intended to be portable. The second swapflags argument
was introduced in Linux 1.3.2.
Примечание (Note)
The partition or path must be prepared with mkswap(8).
There is an upper limit on the number of swap files that may be
used, defined by the kernel constant MAX_SWAPFILES. Before
kernel 2.4.10, MAX_SWAPFILES has the value 8; since kernel
2.4.10, it has the value 32. Since kernel 2.6.18, the limit is
decreased by 2 (thus: 30) if the kernel is built with the
CONFIG_MIGRATION option (which reserves two swap table entries
for the page migration features of mbind(2) and
migrate_pages(2)). Since kernel 2.6.32, the limit is further
decreased by 1 if the kernel is built with the
CONFIG_MEMORY_FAILURE option.
Discard of swap pages was introduced in kernel 2.6.29, then made
conditional on the SWAP_FLAG_DISCARD flag in kernel 2.6.36, which
still discards the entire swap area when swapon() is called, even
if that flag bit is not set.
Смотри также (See also)
mkswap(8), swapoff(8), swapon(8)
