include/linux/lru_cache.h

1 /* SPDX-License-Identifier: GPL-2.0-or-later */
7    Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
8    Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
9    Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
24 This header file (and its .c file; kernel-doc of functions see there)
42   we need to resync all regions that have been target of in-flight WRITE IO
48   This is known as "write intent log", and can be implemented as on-disk
53   in-flight WRITE IO, e.g. by only lazily clearing the on-disk write-intent
64   [*] usually as a result of a cluster split-brain and insufficient protection.
68   Having it fine-grained reduces the amount of resync traffic.
76   The on-disk "dirty bitmap" may be re-used as "write-intent" bitmap as well.
77   To reduce the frequency of bitmap updates for write-intent log purposes,
79   on-disk bitmap, while keeping the in-memory "dirty" bitmap as clean as
80   possible, flushing it to disk again when a previously "hot" (and on-disk
86   for write-intent log purposes, additionally to the fine grained dirty bitmap.
96   fixed (but configurable) number of slots which we can identify by index, and
99   change itself (index: -old_label, +new_label), and which index is associated
124  * region number (label) easily.  To do the label -> object lookup without a
142  * them, as the change "index: -old_label, +LC_FREE" would need a transaction
151 	/* back "pointer" into lc_cache->element[index],
165 	/* the least recently used item is kept at lru->prev */
171 	/* the pre-created kmem cache to allocate the objects from */
198 	/* see below: flag-bits for lru_cache */
210 /* flag-bits for lru_cache */
259  * lc_try_lock_for_transaction - can be used to stop lc_get() from changing the tracked set
268 	return !test_and_set_bit(__LC_LOCKED, &lc->flags);  in lc_try_lock_for_transaction()
272  * lc_try_lock - variant to stop lc_get() from changing the tracked set
283  * lc_unlock - unlock @lc, allow lc_get() to change the set again
288 	clear_bit(__LC_DIRTY, &lc->flags);  in lc_unlock()
289 	clear_bit_unlock(__LC_LOCKED, &lc->flags);  in lc_unlock()