Bill J.Xu wrote: > > > After booting my linux box,I add a swap partition using "swapon > > > /dev/hda5".but I found that swap partition was nerver used even > > > 2M physics memory left. > > > > > > why? > > > > Perhaps swap memory will not be used until > > all physical memory has been consumed. > > But I found that other linux box had used swap partition when many > physical RAM left. > > root@FW_knl:/home/shiy# free > total used free shared buffers cached > Mem: 255320 247564 7756 0 15652 197560 > -/+ buffers/cache: 34352 220968 > Swap: 996020 1484 994536 > root@FW_knl:/home/shiy# How long has the first box been up? And how intensive is memory demand on that box? Swap won't be used at all until physical memory becomes close to being exhausted. However, after that point, even if more memory becomes available, data won't be moved back into RAM unless it is actually used. There is often some data which will never be used again (e.g. memory which is used by persistent daemons, but only during the initialisation; the 6 getty processes running on tty1-tty6 which typically never get used on a system which is running X, etc). Such data is a strong candidate for being swapped out; once that happens, it will typically never be swapped in again. So, when a system is booted, there will always be a period when no swap is used. If memory demand is low, that period may last indefinitely. OTOH, once memory demand has been sufficiently high to have required the use of swap, swap usage will probably never drop back to zero. -- Glynn Clements <glynn.clements@xxxxxxxxxx> - : send the line "unsubscribe linux-admin" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
