607fc8f5ea
When I pushed down the page queues lock into pmap_is_modified(), I created an ordering dependence: A pmap operation that clears PG_WRITEABLE and calls vm_page_dirty() must perform the call first. Otherwise, pmap_is_modified() could return FALSE without acquiring the page queues lock because the page is not (currently) writeable, and the caller to pmap_is_modified() might believe that the page's dirty field is clear because it has not seen the effect of the vm_page_dirty() call. When I pushed down the page queues lock into pmap_is_modified(), I overlooked one place where this ordering dependence is violated: pmap_enter(). In a rare situation pmap_enter() can be called to replace a dirty mapping to one page with a mapping to another page. (I say rare because replacements generally occur as a result of a copy-on-write fault, and so the old page is not dirty.) This change delays clearing PG_WRITEABLE until after vm_page_dirty() has been called. Fixing the ordering dependency also makes it easy to introduce a small optimization: When pmap_enter() used to replace a mapping to one page with a mapping to another page, it freed the pv entry for the first mapping and later called the pv entry allocator for the new mapping. Now, pmap_enter() attempts to recycle the old pv entry, saving two calls to the pv entry allocator. |
||
|---|---|---|
| .. | ||
| adm5120 | ||
| alchemy | ||
| atheros | ||
| cavium | ||
| compile | ||
| conf | ||
| idt | ||
| include | ||
| malta | ||
| mips | ||
| rmi | ||
| sentry5 | ||
| sibyte | ||