Re: [PATCH v3 28/49] dm zoned: dynamically allocate the dm-zoned-meta shrinker

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Hi,

On 2023/7/27 16:30, Damien Le Moal wrote:
On 7/27/23 17:04, Qi Zheng wrote:
In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the dm-zoned-meta shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct dmz_metadata.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
  drivers/md/dm-zoned-metadata.c | 28 ++++++++++++++++------------
  1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
index 9d3cca8e3dc9..0bcb26a43578 100644
--- a/drivers/md/dm-zoned-metadata.c
+++ b/drivers/md/dm-zoned-metadata.c
@@ -187,7 +187,7 @@ struct dmz_metadata {
  	struct rb_root		mblk_rbtree;
  	struct list_head	mblk_lru_list;
  	struct list_head	mblk_dirty_list;
-	struct shrinker		mblk_shrinker;
+	struct shrinker		*mblk_shrinker;
/* Zone allocation management */
  	struct mutex		map_lock;
@@ -615,7 +615,7 @@ static unsigned long dmz_shrink_mblock_cache(struct dmz_metadata *zmd,
  static unsigned long dmz_mblock_shrinker_count(struct shrinker *shrink,
  					       struct shrink_control *sc)
  {
-	struct dmz_metadata *zmd = container_of(shrink, struct dmz_metadata, mblk_shrinker);
+	struct dmz_metadata *zmd = shrink->private_data;
return atomic_read(&zmd->nr_mblks);
  }
@@ -626,7 +626,7 @@ static unsigned long dmz_mblock_shrinker_count(struct shrinker *shrink,
  static unsigned long dmz_mblock_shrinker_scan(struct shrinker *shrink,
  					      struct shrink_control *sc)
  {
-	struct dmz_metadata *zmd = container_of(shrink, struct dmz_metadata, mblk_shrinker);
+	struct dmz_metadata *zmd = shrink->private_data;
  	unsigned long count;
spin_lock(&zmd->mblk_lock);
@@ -2936,19 +2936,23 @@ int dmz_ctr_metadata(struct dmz_dev *dev, int num_dev,
  	 */
  	zmd->min_nr_mblks = 2 + zmd->nr_map_blocks + zmd->zone_nr_bitmap_blocks * 16;
  	zmd->max_nr_mblks = zmd->min_nr_mblks + 512;
-	zmd->mblk_shrinker.count_objects = dmz_mblock_shrinker_count;
-	zmd->mblk_shrinker.scan_objects = dmz_mblock_shrinker_scan;
-	zmd->mblk_shrinker.seeks = DEFAULT_SEEKS;
/* Metadata cache shrinker */
-	ret = register_shrinker(&zmd->mblk_shrinker, "dm-zoned-meta:(%u:%u)",
-				MAJOR(dev->bdev->bd_dev),
-				MINOR(dev->bdev->bd_dev));
-	if (ret) {
-		dmz_zmd_err(zmd, "Register metadata cache shrinker failed");
+	zmd->mblk_shrinker = shrinker_alloc(0,  "dm-zoned-meta:(%u:%u)",
+					    MAJOR(dev->bdev->bd_dev),
+					    MINOR(dev->bdev->bd_dev));
+	if (!zmd->mblk_shrinker) {
+		dmz_zmd_err(zmd, "Allocate metadata cache shrinker failed");

ret is not set here, so dmz_ctr_metadata() will return success. You need to add:
		ret = -ENOMEM;
or something.

Indeed, will fix.

  		goto err;
  	}
+ zmd->mblk_shrinker->count_objects = dmz_mblock_shrinker_count;
+	zmd->mblk_shrinker->scan_objects = dmz_mblock_shrinker_scan;
+	zmd->mblk_shrinker->seeks = DEFAULT_SEEKS;
+	zmd->mblk_shrinker->private_data = zmd;
+
+	shrinker_register(zmd->mblk_shrinker);

I fail to see how this new shrinker API is better... Why isn't there a
shrinker_alloc_and_register() function ? That would avoid adding all this code
all over the place as the new API call would be very similar to the current
shrinker_register() call with static allocation.

In some registration scenarios, memory needs to be allocated in advance.
So we continue to use the previous prealloc/register_prepared()
algorithm. The shrinker_alloc_and_register() is just a helper function
that combines the two, and this increases the number of APIs that
shrinker exposes to the outside, so I choose not to add this helper.

Thanks,
Qi


+
  	dmz_zmd_info(zmd, "DM-Zoned metadata version %d", zmd->sb_version);
  	for (i = 0; i < zmd->nr_devs; i++)
  		dmz_print_dev(zmd, i);
@@ -2995,7 +2999,7 @@ int dmz_ctr_metadata(struct dmz_dev *dev, int num_dev,
   */
  void dmz_dtr_metadata(struct dmz_metadata *zmd)
  {
-	unregister_shrinker(&zmd->mblk_shrinker);
+	shrinker_free(zmd->mblk_shrinker);
  	dmz_cleanup_metadata(zmd);
  	kfree(zmd);
  }




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