original development tree for Linux kernel GTP module; now long in mainline.
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* This struct is used to pass information from page reclaim to the shrinkers.
* We consolidate the values for easier extention later.
* The 'gfpmask' refers to the allocation we are currently trying to
* fulfil.
* Note that 'shrink' will be passed nr_to_scan == 0 when the VM is
* querying the cache size, so a fastpath for that case is appropriate.
struct shrink_control {
gfp_t gfp_mask;
/* How many slab objects shrinker() should scan and try to reclaim */
unsigned long nr_to_scan;
/* shrink from these nodes */
nodemask_t nodes_to_scan;
/* current node being shrunk (for NUMA aware shrinkers) */
int nid;
#define SHRINK_STOP (~0UL)
* A callback you can register to apply pressure to ageable caches.
* @shrink() should look through the least-recently-used 'nr_to_scan' entries
* and attempt to free them up. It should return the number of objects which
* remain in the cache. If it returns -1, it means it cannot do any scanning at
* this time (eg. there is a risk of deadlock).
* @count_objects should return the number of freeable items in the cache. If
* there are no objects to free or the number of freeable items cannot be
* determined, it should return 0. No deadlock checks should be done during the
* count callback - the shrinker relies on aggregating scan counts that couldn't
* be executed due to potential deadlocks to be run at a later call when the
* deadlock condition is no longer pending.
* @scan_objects will only be called if @count_objects returned a non-zero
* value for the number of freeable objects. The callout should scan the cache
* and attempt to free items from the cache. It should then return the number
* of objects freed during the scan, or SHRINK_STOP if progress cannot be made
* due to potential deadlocks. If SHRINK_STOP is returned, then no further
* attempts to call the @scan_objects will be made from the current reclaim
* context.
* @flags determine the shrinker abilities, like numa awareness
struct shrinker {
int (*shrink)(struct shrinker *, struct shrink_control *sc);
unsigned long (*count_objects)(struct shrinker *,
struct shrink_control *sc);
unsigned long (*scan_objects)(struct shrinker *,
struct shrink_control *sc);
int seeks; /* seeks to recreate an obj */
long batch; /* reclaim batch size, 0 = default */
unsigned long flags;
/* These are for internal use */
struct list_head list;
/* objs pending delete, per node */
atomic_long_t *nr_deferred;
#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
/* Flags */
#define SHRINKER_NUMA_AWARE (1 << 0)
extern int register_shrinker(struct shrinker *);
extern void unregister_shrinker(struct shrinker *);