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When the system runs low on physical memory, it can "swap" portions of RAM to the paging file to make room for new data, as well as to read previously swapped information back into RAM. Excessive use of this mechanism results in thrashing and generally hampers overall system performance, mainly because hard drives are far slower than RAM.
zram, formerly called compcache, is a Linux kernel module for creating a compressed block device in RAM, i.e. a RAM disk with on-the-fly disk compression. The block device created with zram can then be used for swap or as general-purpose RAM disk. The two most common uses for zram are for the storage of temporary files (/tmp) and as a swap ...
When every process is waiting on the swap, the system is considered to be in swap death. [24] [25] Swap death can happen due to incorrectly configured memory overcommitment. [26] [27] [28] The original description of the "swapping to death" problem relates to the X server. If code or data used by the X server to respond to a keystroke is not in ...
In comparison, zswap acts as a RAM-based cache for swap devices. This provides zswap with an eviction mechanism for less used swapped pages, which zram lacked until the introduction of CONFIG_ZRAM_WRITEBACK in kernel version 4.14. Though, as a result of its design, at least one already existing swap device is required for zswap to be used. [16]
When a hot-swap component is inserted its input and output signal pins will represent a temporary short-circuit to ground. This can cause unwanted ground-level pulses on the signals which can disturb the operation of other hot-swap components in the system. This was a problem for early parallel SCSI disk-drives. One common design solution is to ...
By reducing the I/O activity caused by paging requests, virtual memory compression can produce overall performance improvements. The degree of performance improvement depends on a variety of factors, including the availability of any compression co-processors, spare bandwidth on the CPU, speed of the I/O channel, speed of the physical memory, and the compressibility of the physical memory ...
A system thrashing is often a result of a sudden spike in page demand from a small number of running programs. Swap-token [3] is a lightweight and dynamic thrashing protection mechanism. The basic idea is to set a token in the system, which is randomly given to a process that has page faults when thrashing happens.
For example, the C64 used bank switching to allow for a full 64 KB of RAM and still provide for ROM and memory-mapped I/O as well. The Atari 130XE could allow its two processors (the 6502 and the ANTIC ) to access separate RAM banks, allowing programmers to make large playfields and other graphic objects without using up the memory visible to ...