/* * Overview of UVM page flags. * * Locking notes: * * PG_, struct vm_page::flags => locked by owner * PQ_, struct vm_page::pqflags => locked by uvm_pageqlock * PQ_FREE => additionally locked by uvm_fpageqlock * * Flag descriptions: * * PG_BUSY: * Page is long-term locked, usually because of I/O (transfer from the * page memory to the backing store) is in progress. LWP attempting * to access the page shall set PG_WANTED and wait. * * PG_WANTED: * Indicates that the page, which is currently PG_BUSY, is wanted by * some other LWP. The page owner (i.e. LWP which set PG_BUSY) is * responsible to clear both flags and wake up any waiters once it has * released the long-term lock (PG_BUSY). * * PG_RELEASED: * Indicates that the page, which is currently PG_BUSY, should be freed * after the release of long-term lock. It is responsibility of the * owning LWP (i.e. which set PG_BUSY) to do it. * * PG_CLEAN: * Page has not been modified since it was loaded from the backing * store. If this flag is not set, page is considered "dirty". * XXX: Currently it means that the page *might* be clean; will be * fixed with yamt-pagecache merge. * * PG_FAKE: * Page has been allocated, but not yet initialised. The flag is used * to avoid overwriting of valid data, e.g. to prevent read from the * backing store when in-core data is newer. * * PG_TABLED: * Indicates that the page is currently in the object's offset queue, * and that it should be removed from it once the page is freed. Used * diagnostic purposes. * * PG_PAGEOUT: * Indicates that the page is being paged-out in preparation for * being freed. * * PG_RDONLY: * Indicates that the page must be mapped read-only. * * PG_ZERO: * Indicates that the page has been pre-zeroed. This flag is only * set when the page is not in the queues and is cleared when the * page is placed on the free list. * * PG_MARKER: * Dummy marker page. */