Red Hat Enterprise Linux 5 Administration Unleashed

Optimizing Virtual Memory 427TABLE 21.1Continuedvm.nr_hugepages 0vm.swappiness 60vm.nr_pdflush_threads 2vm.dirty_expire_centisecs 3000vm.dirty_writeback_centisecs 500vm.dirty_ratio 40vm.dirty_background_ratio 10vm.page-cluster 3vm.overcommit_ratio 50vm.overcommit_memory 0vm.min_slab_ratio 5*vm.min_unmapped_ratio 1*vm.panic_on_oom 0*These tunables are only available for kernels with NUMA support.21The following explains each of these settings:. vm.swap_token_timeoutLength of the swap out protection token, in seconds. Used to prevent needless pagefaults in a thrashing state.. vm.legacy_va_layoutIf the system’s architecture allows it, this parameter allows the 2.4 kernel layoutalgorithm for allocating virtual memory for processes.. vm.vfs_cache_pressureControls how aggressive the kernel is in reclaiming memory used as cache for directoryand inode objects. The higher the value, the more aggressive the kernel is inreclaiming this type of memory.. vm.block_dumpIf set to a non-zero value and syslog is set to record debug messages from the kernel,messages about I/O requests and page writes are logged in /var/log/messages.. vm.laptop_modeMinimizes power consumption used for writes to the disk such as performing writeoperations when the disk is already being used. Automatically enabled when thelaptop is using the battery if the system uses ACPI. For more details, install thekernel-doc package and read the /usr/share/doc/kernel-doc-/Documentation/laptop-mode.txt file.. vm.max_map_countMaximum number of memory map areas the kernel will allocate each process.