Documentation/vm/page_migration.rst

167 To overcome the problem, VM supports non-LRU page migration which provides
176    What VM expects from isolate_page() function of driver is to return *true*
177    if driver isolates the page successfully. On returning true, VM marks the page
181    Once page is successfully isolated, VM uses page.lru fields so driver
187    After isolation, VM calls migratepage() of driver with the isolated page.
191    indicate to the VM the oldpage is no longer movable via __ClearPageMovable()
194    can return -EAGAIN. On -EAGAIN, VM will retry page migration in a short time
195    because VM interprets -EAGAIN as "temporary migration failure". On returning
196    any error except -EAGAIN, VM will give up the page migration without
203    If migration fails on the isolated page, VM should return the isolated page
204    to the driver so VM calls the driver's putback_page() with the isolated page.
219      family functions which will be called by VM. Exactly speaking,
220      PG_movable is not a real flag of struct page. Rather, VM
230      For testing of non-LRU movable pages, VM supports __PageMovable() function.
233      If the driver releases the page after isolation by VM, page->mapping
241      For guaranteeing non-LRU movable page, VM provides PageMovable() function.
251      To prevent concurrent isolation among several CPUs, VM marks isolated page
254      flag because VM will set/clear it automatically. Keep in mind that if the
256      VM so it shouldn't touch the page.lru field.