From 24f7c6b981fb70084757382da464ea85d72af300 Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Wed, 28 Aug 2013 10:17:56 +1000 Subject: [PATCH] mm: new shrinker API MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The current shrinker callout API uses an a single shrinker call for multiple functions. To determine the function, a special magical value is passed in a parameter to change the behaviour. This complicates the implementation and return value specification for the different behaviours. Separate the two different behaviours into separate operations, one to return a count of freeable objects in the cache, and another to scan a certain number of objects in the cache for freeing. In defining these new operations, ensure the return values and resultant behaviours are clearly defined and documented. Modify shrink_slab() to use the new API and implement the callouts for all the existing shrinkers. Signed-off-by: Dave Chinner Signed-off-by: Glauber Costa Acked-by: Mel Gorman Cc: "Theodore Ts'o" Cc: Adrian Hunter Cc: Al Viro Cc: Artem Bityutskiy Cc: Arve Hjønnevåg Cc: Carlos Maiolino Cc: Christoph Hellwig Cc: Chuck Lever Cc: Daniel Vetter Cc: David Rientjes Cc: Gleb Natapov Cc: Greg Thelen Cc: J. Bruce Fields Cc: Jan Kara Cc: Jerome Glisse Cc: John Stultz Cc: KAMEZAWA Hiroyuki Cc: Kent Overstreet Cc: Kirill A. Shutemov Cc: Marcelo Tosatti Cc: Mel Gorman Cc: Steven Whitehouse Cc: Thomas Hellstrom Cc: Trond Myklebust Signed-off-by: Andrew Morton Signed-off-by: Al Viro --- include/linux/shrinker.h | 38 +++++++++++++++++++------ mm/vmscan.c | 60 ++++++++++++++++++++++++++-------------- 2 files changed, 69 insertions(+), 29 deletions(-) diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h index ac6b8ee07825..884e76222e1b 100644 --- a/include/linux/shrinker.h +++ b/include/linux/shrinker.h @@ -4,6 +4,12 @@ /* * 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; @@ -12,23 +18,37 @@ struct shrink_control { unsigned long nr_to_scan; }; +#define SHRINK_STOP (~0UL) /* * A callback you can register to apply pressure to ageable caches. * - * 'sc' is passed shrink_control which includes a count 'nr_to_scan' - * and a 'gfpmask'. It 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). + * @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). * - * The 'gfpmask' refers to the allocation we are currently trying to - * fulfil. + * @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. * - * 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. + * @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. */ 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 */ diff --git a/mm/vmscan.c b/mm/vmscan.c index 2cff0d491c6d..4d4e859b4b9c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -205,19 +205,24 @@ static inline int do_shrinker_shrink(struct shrinker *shrinker, * * Returns the number of slab objects which we shrunk. */ -unsigned long shrink_slab(struct shrink_control *shrink, +unsigned long shrink_slab(struct shrink_control *shrinkctl, unsigned long nr_pages_scanned, unsigned long lru_pages) { struct shrinker *shrinker; - unsigned long ret = 0; + unsigned long freed = 0; if (nr_pages_scanned == 0) nr_pages_scanned = SWAP_CLUSTER_MAX; if (!down_read_trylock(&shrinker_rwsem)) { - /* Assume we'll be able to shrink next time */ - ret = 1; + /* + * If we would return 0, our callers would understand that we + * have nothing else to shrink and give up trying. By returning + * 1 we keep it going and assume we'll be able to shrink next + * time. + */ + freed = 1; goto out; } @@ -225,14 +230,16 @@ unsigned long shrink_slab(struct shrink_control *shrink, unsigned long long delta; long total_scan; long max_pass; - int shrink_ret = 0; long nr; long new_nr; long batch_size = shrinker->batch ? shrinker->batch : SHRINK_BATCH; - max_pass = do_shrinker_shrink(shrinker, shrink, 0); - if (max_pass <= 0) + if (shrinker->count_objects) + max_pass = shrinker->count_objects(shrinker, shrinkctl); + else + max_pass = do_shrinker_shrink(shrinker, shrinkctl, 0); + if (max_pass == 0) continue; /* @@ -248,8 +255,8 @@ unsigned long shrink_slab(struct shrink_control *shrink, do_div(delta, lru_pages + 1); total_scan += delta; if (total_scan < 0) { - printk(KERN_ERR "shrink_slab: %pF negative objects to " - "delete nr=%ld\n", + printk(KERN_ERR + "shrink_slab: %pF negative objects to delete nr=%ld\n", shrinker->shrink, total_scan); total_scan = max_pass; } @@ -277,20 +284,33 @@ unsigned long shrink_slab(struct shrink_control *shrink, if (total_scan > max_pass * 2) total_scan = max_pass * 2; - trace_mm_shrink_slab_start(shrinker, shrink, nr, + trace_mm_shrink_slab_start(shrinker, shrinkctl, nr, nr_pages_scanned, lru_pages, max_pass, delta, total_scan); while (total_scan >= batch_size) { - int nr_before; - nr_before = do_shrinker_shrink(shrinker, shrink, 0); - shrink_ret = do_shrinker_shrink(shrinker, shrink, - batch_size); - if (shrink_ret == -1) - break; - if (shrink_ret < nr_before) - ret += nr_before - shrink_ret; + if (shrinker->scan_objects) { + unsigned long ret; + shrinkctl->nr_to_scan = batch_size; + ret = shrinker->scan_objects(shrinker, shrinkctl); + + if (ret == SHRINK_STOP) + break; + freed += ret; + } else { + int nr_before; + long ret; + + nr_before = do_shrinker_shrink(shrinker, shrinkctl, 0); + ret = do_shrinker_shrink(shrinker, shrinkctl, + batch_size); + if (ret == -1) + break; + if (ret < nr_before) + freed += nr_before - ret; + } + count_vm_events(SLABS_SCANNED, batch_size); total_scan -= batch_size; @@ -308,12 +328,12 @@ unsigned long shrink_slab(struct shrink_control *shrink, else new_nr = atomic_long_read(&shrinker->nr_in_batch); - trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr); + trace_mm_shrink_slab_end(shrinker, freed, nr, new_nr); } up_read(&shrinker_rwsem); out: cond_resched(); - return ret; + return freed; } static inline int is_page_cache_freeable(struct page *page)