Re: [PATCH v3 08/30] block: Introduce zone write plugging

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On 3/27/24 5:43 PM, Damien Le Moal wrote:
+	/*
+	 * Initialize the zoen write plug with an extra reference so that
+	 * it is not freed when the zone write plug becomes idle without
+	 * the zone being full.
+	 */

zoen -> zone

+static void disk_zone_wplugs_work(struct work_struct *work)
+{
+	struct gendisk *disk =
+		container_of(work, struct gendisk, zone_wplugs_work);
+	struct blk_zone_wplug *zwplug;
+	unsigned long flags;
+
+	spin_lock_irqsave(&disk->zone_wplugs_lock, flags);
+
+	while (!list_empty(&disk->zone_wplugs_err_list)) {
+		zwplug = list_first_entry(&disk->zone_wplugs_err_list,
+					  struct blk_zone_wplug, link);
+		list_del_init(&zwplug->link);
+		blk_get_zone_wplug(zwplug);
+		spin_unlock_irqrestore(&disk->zone_wplugs_lock, flags);
+
+		disk_zone_wplug_handle_error(disk, zwplug);
+		disk_put_zone_wplug(zwplug);
+
+		spin_lock_irqsave(&disk->zone_wplugs_lock, flags);
+	}
+
+	spin_unlock_irqrestore(&disk->zone_wplugs_lock, flags);
+}

What is the maximum number of iterations the above while loop can perform? I'm wondering whether a cond_resched() call should be added.

+
+	/* Wait for the zone write plugs to be RCU-freed. */
+	rcu_barrier();
+}

It is not clear to me why the above rcu_barrier() call is necessary? I'm
not aware of any other kernel code where kfree_rcu() is followed by an
rcu_barrier() call.

+static int disk_alloc_zone_resources(struct gendisk *disk,
+				     unsigned int max_nr_zwplugs)
+{
+	unsigned int i;
+
+	disk->zone_wplugs_hash_bits =
+		min(ilog2(max_nr_zwplugs) + 1, BLK_ZONE_MAX_WPLUG_HASH_BITS);

If max_nr_zwplugs is a power of two, the above formula will result in a
hash table with a size that is twice the size of max_nr_zwplugs.
Shouldn't ilog2(max_nr_zwplugs) + 1 be changed into
ilog2(roundup_pow_of_two(max_nr_zwplugs))?

Otherwise this patch looks fine to me.

Thanks,

Bart.




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