Index: head/en_US.ISO8859-1/books/faq/book.xml =================================================================== --- head/en_US.ISO8859-1/books/faq/book.xml +++ head/en_US.ISO8859-1/books/faq/book.xml @@ -4003,7 +4003,7 @@ top mean? - + @@ -4017,24 +4017,15 @@ - Cache: (most often) pages that - have percolated from inactive to a status where they - maintain their data, but can often be immediately - reused (either with their old association, or reused - with a new association). There can be certain - immediate transitions from active - to cache state if the page is known - to be clean (unmodified), but that transition is a - matter of policy, depending upon the algorithm choice - of the VM system maintainer. + Laundry: pages recently + statistically unused but known to be dirty, that is, + whose contents needs to be paged out before they can + be reused. Free: pages without data - content, and can be immediately used in certain - circumstances where cache pages might be ineligible. - Free pages can be reused at interrupt or process - state. + content, which can be immediately reused. @@ -4045,21 +4036,19 @@ Pages are most often written to disk (sort of a VM - sync) when they are in the inactive state, but active - pages can also be synced. This depends upon the CPU - tracking of the modified bit being available, and in + sync) when they are in the laundry state, but active or + inactive pages can also be synced. This depends upon the + CPU tracking of the modified bit being available, and in certain situations there can be an advantage for a block - of VM pages to be synced, whether they are active or - inactive. In most common cases, it is best to think of - the inactive queue to be a queue of relatively unused + of VM pages to be synced, regardless of the queue they + belong to. In most common cases, it is best to think of + the laundry queue as a queue of relatively unused pages that might or might not be in the process of being - written to disk. Cached pages are already synced, not - mapped, but available for immediate process use with their - old association or with a new association. Free pages are - available at interrupt level, but cached or free pages can - be used at process state for reuse. Cache pages are not - adequately locked to be available at interrupt - level. + written to disk. The inactive queue contains a mix of + clean and dirty pages; clean pages near the head of the + queue are reclaimed immediately to alleviate a free page + shortage, and dirty pages are moved to the laundry queue + for deferred processing. There are some other flags (e.g., busy flag or busy count) that might modify some of the described @@ -4072,17 +4061,19 @@ How much free memory is available? - + There are a couple of kinds of free - memory. One kind is the amount of memory - immediately available without paging anything else out. - That is approximately the size of cache queue + size of - free queue (with a derating factor, depending upon system - tuning). Another kind of free memory is - the total amount of VM space. That can - be complex, but is dependent upon the amount of swap space - and memory. Other kinds of free memory + memory. The most common is the amount of memory + immediately available without reclaiming memory already + in use. That is the size of the free pages queue plus + some other reserved pages. This amount is exported by the + vm.stats.vm.v_free_count + &man.sysctl.8;, shown, for instance, by &man.top.1;. + Another kind of free memory is + the total amount of virtual memory available to userland + processes, which depends on the sum of swap space and + usable memory. Other kinds of free memory descriptions are also possible, but it is relatively useless to define these, but rather it is important to make sure that the paging rate is kept low, and to avoid