Author: markj Date: Tue Aug 4 14:59:43 2020 New Revision: 363840 URL: https://svnweb.freebsd.org/changeset/base/363840
Log: Remove most lingering references to the page lock in comments. Finish updating comments to reflect new locking protocols introduced over the past year. In particular, vm_page_lock is now effectively unused. Reviewed by: kib Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D25868 Modified: head/sys/vm/vm_page.c head/sys/vm/vm_page.h head/sys/vm/vm_pageout.c head/sys/vm/vnode_pager.c Modified: head/sys/vm/vm_page.c ============================================================================== --- head/sys/vm/vm_page.c Tue Aug 4 14:53:41 2020 (r363839) +++ head/sys/vm/vm_page.c Tue Aug 4 14:59:43 2020 (r363840) @@ -2675,7 +2675,7 @@ retry: * ascending order.) (2) It is not reserved, and it is * transitioning from free to allocated. (Conversely, * the transition from allocated to free for managed - * pages is blocked by the page lock.) (3) It is + * pages is blocked by the page busy lock.) (3) It is * allocated but not contained by an object and not * wired, e.g., allocated by Xen's balloon driver. */ @@ -3622,8 +3622,6 @@ vm_page_pqbatch_drain(void) * Request removal of the given page from its current page * queue. Physical removal from the queue may be deferred * indefinitely. - * - * The page must be locked. */ void vm_page_dequeue_deferred(vm_page_t m) @@ -3804,8 +3802,8 @@ vm_page_free_prep(vm_page_t m) * Returns the given page to the free list, disassociating it * from any VM object. * - * The object must be locked. The page must be locked if it is - * managed. + * The object must be locked. The page must be exclusively busied if it + * belongs to an object. */ static void vm_page_free_toq(vm_page_t m) @@ -3834,9 +3832,6 @@ vm_page_free_toq(vm_page_t m) * Returns a list of pages to the free list, disassociating it * from any VM object. In other words, this is equivalent to * calling vm_page_free_toq() for each page of a list of VM objects. - * - * The objects must be locked. The pages must be locked if it is - * managed. */ void vm_page_free_pages_toq(struct spglist *free, bool update_wire_count) @@ -3974,8 +3969,6 @@ vm_page_unwire_managed(vm_page_t m, uint8_t nqueue, bo * of wirings transitions to zero and the page is eligible for page out, then * the page is added to the specified paging queue. If the released wiring * represented the last reference to the page, the page is freed. - * - * A managed page must be locked. */ void vm_page_unwire(vm_page_t m, uint8_t nqueue) @@ -4022,8 +4015,6 @@ vm_page_unwire_noq(vm_page_t m) * Ensure that the page ends up in the specified page queue. If the page is * active or being moved to the active queue, ensure that its act_count is * at least ACT_INIT but do not otherwise mess with it. - * - * A managed page must be locked. */ static __always_inline void vm_page_mvqueue(vm_page_t m, const uint8_t nqueue, const uint16_t nflag) @@ -4269,14 +4260,14 @@ vm_page_try_remove_write(vm_page_t m) * vm_page_advise * * Apply the specified advice to the given page. - * - * The object and page must be locked. */ void vm_page_advise(vm_page_t m, int advice) { VM_OBJECT_ASSERT_WLOCKED(m->object); + vm_page_assert_xbusied(m); + if (advice == MADV_FREE) /* * Mark the page clean. This will allow the page to be freed Modified: head/sys/vm/vm_page.h ============================================================================== --- head/sys/vm/vm_page.h Tue Aug 4 14:53:41 2020 (r363839) +++ head/sys/vm/vm_page.h Tue Aug 4 14:59:43 2020 (r363840) @@ -95,19 +95,17 @@ * synchronized using either one of or a combination of locks. If a * field is annotated with two of these locks then holding either is * sufficient for read access but both are required for write access. - * The physical address of a page is used to select its page lock from - * a pool. The queue lock for a page depends on the value of its queue - * field and is described in detail below. + * The queue lock for a page depends on the value of its queue field and is + * described in detail below. * * The following annotations are possible: * (A) the field must be accessed using atomic(9) and may require * additional synchronization. * (B) the page busy lock. * (C) the field is immutable. - * (F) the per-domain lock for the free queues + * (F) the per-domain lock for the free queues. * (M) Machine dependent, defined by pmap layer. * (O) the object that the page belongs to. - * (P) the page lock. * (Q) the page's queue lock. * * The busy lock is an embedded reader-writer lock that protects the @@ -270,7 +268,7 @@ struct vm_page { * cleared only when the corresponding object's write lock is held. * * VPRC_BLOCKED is used to atomically block wirings via pmap lookups while - * attempting to tear down all mappings of a given page. The page lock and + * attempting to tear down all mappings of a given page. The page busy lock and * object write lock must both be held in order to set or clear this bit. */ #define VPRC_BLOCKED 0x40000000u /* mappings are being removed */ @@ -411,27 +409,26 @@ extern struct mtx_padalign pa_lock[]; * * PGA_ENQUEUED is set and cleared when a page is inserted into or removed * from a page queue, respectively. It determines whether the plinks.q field - * of the page is valid. To set or clear this flag, the queue lock for the - * page must be held: the page queue lock corresponding to the page's "queue" - * field if its value is not PQ_NONE, and the page lock otherwise. + * of the page is valid. To set or clear this flag, page's "queue" field must + * be a valid queue index, and the corresponding page queue lock must be held. * * PGA_DEQUEUE is set when the page is scheduled to be dequeued from a page * queue, and cleared when the dequeue request is processed. A page may * have PGA_DEQUEUE set and PGA_ENQUEUED cleared, for instance if a dequeue * is requested after the page is scheduled to be enqueued but before it is - * actually inserted into the page queue. For allocated pages, the page lock - * must be held to set this flag, but it may be set by vm_page_free_prep() - * without the page lock held. The page queue lock must be held to clear the - * PGA_DEQUEUE flag. + * actually inserted into the page queue. * * PGA_REQUEUE is set when the page is scheduled to be enqueued or requeued - * in its page queue. The page lock must be held to set this flag, and the - * queue lock for the page must be held to clear it. + * in its page queue. * * PGA_REQUEUE_HEAD is a special flag for enqueuing pages near the head of - * the inactive queue, thus bypassing LRU. The page lock must be held to - * set this flag, and the queue lock for the page must be held to clear it. + * the inactive queue, thus bypassing LRU. * + * The PGA_DEQUEUE, PGA_REQUEUE and PGA_REQUEUE_HEAD flags must be set using an + * atomic RMW operation to ensure that the "queue" field is a valid queue index, + * and the corresponding page queue lock must be held when clearing any of the + * flags. + * * PGA_SWAP_FREE is used to defer freeing swap space to the pageout daemon * when the context that dirties the page does not have the object write lock * held. @@ -451,8 +448,8 @@ extern struct mtx_padalign pa_lock[]; #define PGA_QUEUE_STATE_MASK (PGA_ENQUEUED | PGA_QUEUE_OP_MASK) /* - * Page flags. If changed at any other time than page allocation or - * freeing, the modification must be protected by the vm_page lock. + * Page flags. Updates to these flags are not synchronized, and thus they must + * be set during page allocation or free to avoid races. * * The PG_PCPU_CACHE flag is set at allocation time if the page was * allocated from a per-CPU cache. It is cleared the next time that the Modified: head/sys/vm/vm_pageout.c ============================================================================== --- head/sys/vm/vm_pageout.c Tue Aug 4 14:53:41 2020 (r363839) +++ head/sys/vm/vm_pageout.c Tue Aug 4 14:59:43 2020 (r363840) @@ -257,10 +257,9 @@ vm_pageout_end_scan(struct scan_state *ss) * physically dequeued if the caller so requests. Otherwise, the returned * batch may contain marker pages, and it is up to the caller to handle them. * - * When processing the batch queue, vm_page_queue() must be used to - * determine whether the page has been logically dequeued by another thread. - * Once this check is performed, the page lock guarantees that the page will - * not be disassociated from the queue. + * When processing the batch queue, vm_pageout_defer() must be used to + * determine whether the page has been logically dequeued since the batch was + * collected. */ static __always_inline void vm_pageout_collect_batch(struct scan_state *ss, const bool dequeue) Modified: head/sys/vm/vnode_pager.c ============================================================================== --- head/sys/vm/vnode_pager.c Tue Aug 4 14:53:41 2020 (r363839) +++ head/sys/vm/vnode_pager.c Tue Aug 4 14:59:43 2020 (r363840) @@ -1307,7 +1307,7 @@ vnode_pager_generic_putpages(struct vnode *vp, vm_page * the last page is partially invalid. In this case the filesystem * may not properly clear the dirty bits for the entire page (which * could be VM_PAGE_BITS_ALL due to the page having been mmap()d). - * With the page locked we are free to fix-up the dirty bits here. + * With the page busied we are free to fix up the dirty bits here. * * We do not under any circumstances truncate the valid bits, as * this will screw up bogus page replacement. _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "[email protected]"
