Re: [PATCH v3 20/32] shrinker: Kill old ->shrink API.

[Greg Thelen <gthelen@google.com>]

On Mon, Apr 08 2013, Glauber Costa wrote:

> From: Dave Chinner <dchinner@redhat.com>
>
> There are no more users of this API, so kill it dead, dead, dead and
> quietly bury the corpse in a shallow, unmarked grave in a dark
> forest deep in the hills...
>
> [ glommer: added flowers to the grave ]
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Reviewed-by: Greg Thelen <gthelen@google.com>

> ---
>  include/linux/shrinker.h      | 15 +++++----------
>  include/trace/events/vmscan.h |  4 ++--
>  mm/vmscan.c                   | 40 ++++++++--------------------------------
>  3 files changed, 15 insertions(+), 44 deletions(-)
>
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index e71286f..d4636a0 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -7,14 +7,15 @@
>   *
>   * 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 */
> +	/*
> +	 * How many objects scan_objects should scan and try to reclaim.
> +	 * This is reset before every call, so it is safe for callees
> +	 * to modify.
> +	 */
>  	long nr_to_scan;
>  
>  	/* shrink from these nodes */
> @@ -24,11 +25,6 @@ struct shrink_control {
>  /*
>   * 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
> @@ -44,7 +40,6 @@ struct shrink_control {
>   * @scan_objects will be made from the current reclaim context.
>   */
>  struct shrinker {
> -	int (*shrink)(struct shrinker *, struct shrink_control *sc);
>  	long (*count_objects)(struct shrinker *, struct shrink_control *sc);
>  	long (*scan_objects)(struct shrinker *, struct shrink_control *sc);
>  
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index 63cfccc..132a985 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -202,7 +202,7 @@ TRACE_EVENT(mm_shrink_slab_start,
>  
>  	TP_fast_assign(
>  		__entry->shr = shr;
> -		__entry->shrink = shr->shrink;
> +		__entry->shrink = shr->scan_objects;
>  		__entry->nr_objects_to_shrink = nr_objects_to_shrink;
>  		__entry->gfp_flags = sc->gfp_mask;
>  		__entry->pgs_scanned = pgs_scanned;
> @@ -241,7 +241,7 @@ TRACE_EVENT(mm_shrink_slab_end,
>  
>  	TP_fast_assign(
>  		__entry->shr = shr;
> -		__entry->shrink = shr->shrink;
> +		__entry->shrink = shr->scan_objects;
>  		__entry->unused_scan = unused_scan_cnt;
>  		__entry->new_scan = new_scan_cnt;
>  		__entry->retval = shrinker_retval;
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 6926e09..232dfcb 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -176,14 +176,6 @@ void unregister_shrinker(struct shrinker *shrinker)
>  }
>  EXPORT_SYMBOL(unregister_shrinker);
>  
> -static inline int do_shrinker_shrink(struct shrinker *shrinker,
> -				     struct shrink_control *sc,
> -				     unsigned long nr_to_scan)
> -{
> -	sc->nr_to_scan = nr_to_scan;
> -	return (*shrinker->shrink)(shrinker, sc);
> -}
> -
>  #define SHRINK_BATCH 128
>  /*
>   * Call the shrink functions to age shrinkable caches
> @@ -229,11 +221,8 @@ unsigned long shrink_slab(struct shrink_control *sc,
>  		long batch_size = shrinker->batch ? shrinker->batch
>  						  : SHRINK_BATCH;
>  
> -		if (shrinker->scan_objects) {
> -			max_pass = shrinker->count_objects(shrinker, sc);
> -			WARN_ON(max_pass < 0);
> -		} else
> -			max_pass = do_shrinker_shrink(shrinker, sc, 0);
> +		max_pass = shrinker->count_objects(shrinker, sc);
> +		WARN_ON(max_pass < 0);
>  		if (max_pass <= 0)
>  			continue;
>  
> @@ -252,7 +241,7 @@ unsigned long shrink_slab(struct shrink_control *sc,
>  		if (total_scan < 0) {
>  			printk(KERN_ERR
>  			"shrink_slab: %pF negative objects to delete nr=%ld\n",
> -			       shrinker->shrink, total_scan);
> +			       shrinker->scan_objects, total_scan);
>  			total_scan = max_pass;
>  		}
>  
> @@ -286,24 +275,11 @@ unsigned long shrink_slab(struct shrink_control *sc,
>  		do {
>  			long ret;
>  
> -			if (shrinker->scan_objects) {
> -				sc->nr_to_scan = batch_size;
> -				ret = shrinker->scan_objects(shrinker, sc);
> -
> -				if (ret == -1)
> -					break;
> -				freed += ret;
> -			} else {
> -				int nr_before;
> -
> -				nr_before = do_shrinker_shrink(shrinker, sc, 0);
> -				ret = do_shrinker_shrink(shrinker, sc,
> -								batch_size);
> -				if (ret == -1)
> -					break;
> -				if (ret < nr_before)
> -					freed += nr_before - ret;
> -			}
> +			sc->nr_to_scan = batch_size;
> +			ret = shrinker->scan_objects(shrinker, sc);
> +			if (ret == -1)
> +				break;
> +			freed += ret;
>  
>  			count_vm_events(SLABS_SCANNED, batch_size);
>  			total_scan -= batch_size;

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