netfs: Add folio_queue API documentation

Add API documentation for folio_queue.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/2912369.1727691281@warthog.procyon.org.uk
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-doc@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 168 insertions, 0 deletions

diff --git a/include/linux/folio_queue.h b/include/linux/folio_queue.h
index 955680c3bb5f..af871405ae55 100644
--- a/include/linux/folio_queue.h
+++ b/include/linux/folio_queue.h
@@ -3,6 +3,12 @@
  *
  * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
+ *
+ * See:
+ *
+ *	Documentation/core-api/folio_queue.rst
+ *
+ * for a description of the API.
  */
 
 #ifndef _LINUX_FOLIO_QUEUE_H
@@ -33,6 +39,13 @@ struct folio_queue {
 #endif
 };
 
+/**
+ * folioq_init - Initialise a folio queue segment
+ * @folioq: The segment to initialise
+ *
+ * Initialise a folio queue segment.  Note that the folio pointers are
+ * left uninitialised.
+ */
 static inline void folioq_init(struct folio_queue *folioq)
 {
 	folio_batch_init(&folioq->vec);
@@ -43,62 +56,155 @@ static inline void folioq_init(struct folio_queue *folioq)
 	folioq->marks3 = 0;
 }
 
+/**
+ * folioq_nr_slots: Query the capacity of a folio queue segment
+ * @folioq: The segment to query
+ *
+ * Query the number of folios that a particular folio queue segment might hold.
+ * [!] NOTE: This must not be assumed to be the same for every segment!
+ */
 static inline unsigned int folioq_nr_slots(const struct folio_queue *folioq)
 {
 	return PAGEVEC_SIZE;
 }
 
+/**
+ * folioq_count: Query the occupancy of a folio queue segment
+ * @folioq: The segment to query
+ *
+ * Query the number of folios that have been added to a folio queue segment.
+ * Note that this is not decreased as folios are removed from a segment.
+ */
 static inline unsigned int folioq_count(struct folio_queue *folioq)
 {
 	return folio_batch_count(&folioq->vec);
 }
 
+/**
+ * folioq_count: Query if a folio queue segment is full
+ * @folioq: The segment to query
+ *
+ * Query if a folio queue segment is fully occupied.  Note that this does not
+ * change if folios are removed from a segment.
+ */
 static inline bool folioq_full(struct folio_queue *folioq)
 {
 	//return !folio_batch_space(&folioq->vec);
 	return folioq_count(folioq) >= folioq_nr_slots(folioq);
 }
 
+/**
+ * folioq_is_marked: Check first folio mark in a folio queue segment
+ * @folioq: The segment to query
+ * @slot: The slot number of the folio to query
+ *
+ * Determine if the first mark is set for the folio in the specified slot in a
+ * folio queue segment.
+ */
 static inline bool folioq_is_marked(const struct folio_queue *folioq, unsigned int slot)
 {
 	return test_bit(slot, &folioq->marks);
 }
 
+/**
+ * folioq_mark: Set the first mark on a folio in a folio queue segment
+ * @folioq: The segment to modify
+ * @slot: The slot number of the folio to modify
+ *
+ * Set the first mark for the folio in the specified slot in a folio queue
+ * segment.
+ */
 static inline void folioq_mark(struct folio_queue *folioq, unsigned int slot)
 {
 	set_bit(slot, &folioq->marks);
 }
 
+/**
+ * folioq_unmark: Clear the first mark on a folio in a folio queue segment
+ * @folioq: The segment to modify
+ * @slot: The slot number of the folio to modify
+ *
+ * Clear the first mark for the folio in the specified slot in a folio queue
+ * segment.
+ */
 static inline void folioq_unmark(struct folio_queue *folioq, unsigned int slot)
 {
 	clear_bit(slot, &folioq->marks);
 }
 
+/**
+ * folioq_is_marked2: Check second folio mark in a folio queue segment
+ * @folioq: The segment to query
+ * @slot: The slot number of the folio to query
+ *
+ * Determine if the second mark is set for the folio in the specified slot in a
+ * folio queue segment.
+ */
 static inline bool folioq_is_marked2(const struct folio_queue *folioq, unsigned int slot)
 {
 	return test_bit(slot, &folioq->marks2);
 }
 
+/**
+ * folioq_mark2: Set the second mark on a folio in a folio queue segment
+ * @folioq: The segment to modify
+ * @slot: The slot number of the folio to modify
+ *
+ * Set the second mark for the folio in the specified slot in a folio queue
+ * segment.
+ */
 static inline void folioq_mark2(struct folio_queue *folioq, unsigned int slot)
 {
 	set_bit(slot, &folioq->marks2);
 }
 
+/**
+ * folioq_unmark2: Clear the second mark on a folio in a folio queue segment
+ * @folioq: The segment to modify
+ * @slot: The slot number of the folio to modify
+ *
+ * Clear the second mark for the folio in the specified slot in a folio queue
+ * segment.
+ */
 static inline void folioq_unmark2(struct folio_queue *folioq, unsigned int slot)
 {
 	clear_bit(slot, &folioq->marks2);
 }
 
+/**
+ * folioq_is_marked3: Check third folio mark in a folio queue segment
+ * @folioq: The segment to query
+ * @slot: The slot number of the folio to query
+ *
+ * Determine if the third mark is set for the folio in the specified slot in a
+ * folio queue segment.
+ */
 static inline bool folioq_is_marked3(const struct folio_queue *folioq, unsigned int slot)
 {
 	return test_bit(slot, &folioq->marks3);
 }
 
+/**
+ * folioq_mark3: Set the third mark on a folio in a folio queue segment
+ * @folioq: The segment to modify
+ * @slot: The slot number of the folio to modify
+ *
+ * Set the third mark for the folio in the specified slot in a folio queue
+ * segment.
+ */
 static inline void folioq_mark3(struct folio_queue *folioq, unsigned int slot)
 {
 	set_bit(slot, &folioq->marks3);
 }
 
+/**
+ * folioq_unmark3: Clear the third mark on a folio in a folio queue segment
+ * @folioq: The segment to modify
+ * @slot: The slot number of the folio to modify
+ *
+ * Clear the third mark for the folio in the specified slot in a folio queue
+ * segment.
+ */
 static inline void folioq_unmark3(struct folio_queue *folioq, unsigned int slot)
 {
 	clear_bit(slot, &folioq->marks3);
@@ -111,6 +217,19 @@ static inline unsigned int __folio_order(struct folio *folio)
 	return folio->_flags_1 & 0xff;
 }
 
+/**
+ * folioq_append: Add a folio to a folio queue segment
+ * @folioq: The segment to add to
+ * @folio: The folio to add
+ *
+ * Add a folio to the tail of the sequence in a folio queue segment, increasing
+ * the occupancy count and returning the slot number for the folio just added.
+ * The folio size is extracted and stored in the queue and the marks are left
+ * unmodified.
+ *
+ * Note that it's left up to the caller to check that the segment capacity will
+ * not be exceeded and to extend the queue.
+ */
 static inline unsigned int folioq_append(struct folio_queue *folioq, struct folio *folio)
 {
 	unsigned int slot = folioq->vec.nr++;
@@ -120,6 +239,19 @@ static inline unsigned int folioq_append(struct folio_queue *folioq, struct foli
 	return slot;
 }
 
+/**
+ * folioq_append_mark: Add a folio to a folio queue segment
+ * @folioq: The segment to add to
+ * @folio: The folio to add
+ *
+ * Add a folio to the tail of the sequence in a folio queue segment, increasing
+ * the occupancy count and returning the slot number for the folio just added.
+ * The folio size is extracted and stored in the queue, the first mark is set
+ * and and the second and third marks are left unmodified.
+ *
+ * Note that it's left up to the caller to check that the segment capacity will
+ * not be exceeded and to extend the queue.
+ */
 static inline unsigned int folioq_append_mark(struct folio_queue *folioq, struct folio *folio)
 {
 	unsigned int slot = folioq->vec.nr++;
@@ -130,21 +262,57 @@ static inline unsigned int folioq_append_mark(struct folio_queue *folioq, struct
 	return slot;
 }
 
+/**
+ * folioq_folio: Get a folio from a folio queue segment
+ * @folioq: The segment to access
+ * @slot: The folio slot to access
+ *
+ * Retrieve the folio in the specified slot from a folio queue segment.  Note
+ * that no bounds check is made and if the slot hasn't been added into yet, the
+ * pointer will be undefined.  If the slot has been cleared, NULL will be
+ * returned.
+ */
 static inline struct folio *folioq_folio(const struct folio_queue *folioq, unsigned int slot)
 {
 	return folioq->vec.folios[slot];
 }
 
+/**
+ * folioq_folio_order: Get the order of a folio from a folio queue segment
+ * @folioq: The segment to access
+ * @slot: The folio slot to access
+ *
+ * Retrieve the order of the folio in the specified slot from a folio queue
+ * segment.  Note that no bounds check is made and if the slot hasn't been
+ * added into yet, the order returned will be 0.
+ */
 static inline unsigned int folioq_folio_order(const struct folio_queue *folioq, unsigned int slot)
 {
 	return folioq->orders[slot];
 }
 
+/**
+ * folioq_folio_size: Get the size of a folio from a folio queue segment
+ * @folioq: The segment to access
+ * @slot: The folio slot to access
+ *
+ * Retrieve the size of the folio in the specified slot from a folio queue
+ * segment.  Note that no bounds check is made and if the slot hasn't been
+ * added into yet, the size returned will be PAGE_SIZE.
+ */
 static inline size_t folioq_folio_size(const struct folio_queue *folioq, unsigned int slot)
 {
 	return PAGE_SIZE << folioq_folio_order(folioq, slot);
 }
 
+/**
+ * folioq_clear: Clear a folio from a folio queue segment
+ * @folioq: The segment to clear
+ * @slot: The folio slot to clear
+ *
+ * Clear a folio from a sequence in a folio queue segment and clear its marks.
+ * The occupancy count is left unchanged.
+ */
 static inline void folioq_clear(struct folio_queue *folioq, unsigned int slot)
 {
 	folioq->vec.folios[slot] = NULL;