btrfs: reada: simplify dev->reada_in_flight processing

No need to decrease dev->reada_in_flight in __readahead_hook()'s
internal and reada_extent_put().
reada_extent_put() have no chance to decrease dev->reada_in_flight
in free operation, because reada_extent have additional refcnt when
scheduled to a dev.

We can put inc and dec operation for dev->reada_in_flight to one
place instead to make logic simple and safe, and move useless
reada_extent->scheduled_for to a bool flag instead.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index 5871306a5a3b89e626e69204b836d639c4f9c9c5..9157d789ae86c2e483fcdc2e0fec2f5b531afdfe 100644 (file)
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -72,7 +72,7 @@ struct reada_extent {
        spinlock_t              lock;
        struct reada_zone       *zones[BTRFS_MAX_MIRRORS];
        int                     nzones;
-       struct btrfs_device     *scheduled_for;
+       int                     scheduled;
 };
 
 struct reada_zone {
@@ -115,7 +115,6 @@ static void __readahead_hook(struct btrfs_fs_info *fs_info,
        u64 bytenr;
        u64 generation;
        struct list_head list;
-       struct btrfs_device *for_dev;
 
        if (eb)
                level = btrfs_header_level(eb);
@@ -126,8 +125,7 @@ static void __readahead_hook(struct btrfs_fs_info *fs_info,
         * don't need the lock anymore
         */
        list_replace_init(&re->extctl, &list);
-       for_dev = re->scheduled_for;
-       re->scheduled_for = NULL;
+       re->scheduled = 0;
        spin_unlock(&re->lock);
 
        /*
@@ -212,9 +210,6 @@ cleanup:
                reada_extent_put(fs_info, re);  /* one ref for each entry */
        }
 
-       if (for_dev)
-               atomic_dec(&for_dev->reada_in_flight);
-
        return;
 }
 
@@ -535,8 +530,6 @@ static void reada_extent_put(struct btrfs_fs_info *fs_info,
                kref_put(&zone->refcnt, reada_zone_release);
                spin_unlock(&fs_info->reada_lock);
        }
-       if (re->scheduled_for)
-               atomic_dec(&re->scheduled_for->reada_in_flight);
 
        kfree(re);
 }
@@ -702,12 +695,12 @@ static int reada_start_machine_dev(struct btrfs_fs_info *fs_info,
        spin_unlock(&fs_info->reada_lock);
 
        spin_lock(&re->lock);
-       if (re->scheduled_for || list_empty(&re->extctl)) {
+       if (re->scheduled || list_empty(&re->extctl)) {
                spin_unlock(&re->lock);
                reada_extent_put(fs_info, re);
                return 0;
        }
-       re->scheduled_for = dev;
+       re->scheduled = 1;
        spin_unlock(&re->lock);
 
        /*
@@ -732,6 +725,7 @@ static int reada_start_machine_dev(struct btrfs_fs_info *fs_info,
        if (eb)
                free_extent_buffer(eb);
 
+       atomic_dec(&dev->reada_in_flight);
        reada_extent_put(fs_info, re);
 
        return 1;
@@ -850,10 +844,9 @@ static void dump_devs(struct btrfs_fs_info *fs_info, int all)
                        if (ret == 0)
                                break;
                        printk(KERN_DEBUG
-                               "  re: logical %llu size %u empty %d for %lld",
+                               "  re: logical %llu size %u empty %d scheduled %d",
                                re->logical, fs_info->tree_root->nodesize,
-                               list_empty(&re->extctl), re->scheduled_for ?
-                               re->scheduled_for->devid : -1);
+                               list_empty(&re->extctl), re->scheduled);
 
                        for (i = 0; i < re->nzones; ++i) {
                                printk(KERN_CONT " zone %llu-%llu devs",
@@ -880,15 +873,14 @@ static void dump_devs(struct btrfs_fs_info *fs_info, int all)
                                             index, 1);
                if (ret == 0)
                        break;
-               if (!re->scheduled_for) {
+               if (!re->scheduled) {
                        index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
                        continue;
                }
                printk(KERN_DEBUG
-                       "re: logical %llu size %u list empty %d for %lld",
+                       "re: logical %llu size %u list empty %d scheduled %d",
                        re->logical, fs_info->tree_root->nodesize,
-                       list_empty(&re->extctl),
-                       re->scheduled_for ? re->scheduled_for->devid : -1);
+                       list_empty(&re->extctl), re->scheduled);
                for (i = 0; i < re->nzones; ++i) {
                        printk(KERN_CONT " zone %llu-%llu devs",
                                re->zones[i]->start,