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mm: new shrinker API

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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 <dchinner@redhat.com>
Signed-off-by: Glauber Costa <glommer@parallels.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Rientjes <rientjes@google.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: J. Bruce Fields <bfields@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Dave Chinner 2013-08-28 10:17:56 +10:00 committed by Al Viro
parent dd1f6b2e43
commit 24f7c6b981
2 changed files with 69 additions and 29 deletions
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38
include/linux/shrinker.h
View File

@ -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 */

60
mm/vmscan.c
View File

@ -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)