btrfs: remove the io_pages field in struct extent_buffer

No need to track the number of pages under I/O now that each
extent_buffer is read and written using a single bio.  For the
read side we need to grab an extra reference for the duration of
the I/O to prevent eviction, though.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index eebcef557bd8c7b0ad68e8784291a29764e90551..d8e6c8d5ed9862742da774c874cfcf31abd1c3e7 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1767,8 +1767,6 @@ static void extent_buffer_write_end_io(struct btrfs_bio *bbio)
                struct page *page = bvec->bv_page;
                u32 len = bvec->bv_len;
 
-               atomic_dec(&eb->io_pages);
-
                if (!uptodate) {
                        btrfs_page_clear_uptodate(fs_info, page, start, len);
                        btrfs_page_set_error(fs_info, page, start, len);
@@ -1791,7 +1789,6 @@ static void prepare_eb_write(struct extent_buffer *eb)
        unsigned long end;
 
        clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
-       atomic_set(&eb->io_pages, num_extent_pages(eb));
 
        /* Set btree blocks beyond nritems with 0 to avoid stale content */
        nritems = btrfs_header_nritems(eb);
@@ -3235,8 +3232,7 @@ static void __free_extent_buffer(struct extent_buffer *eb)
 
 static int extent_buffer_under_io(const struct extent_buffer *eb)
 {
-       return (atomic_read(&eb->io_pages) ||
-               test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
+       return (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
                test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
 }
 
@@ -3372,7 +3368,6 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
 
        spin_lock_init(&eb->refs_lock);
        atomic_set(&eb->refs, 1);
-       atomic_set(&eb->io_pages, 0);
 
        ASSERT(len <= BTRFS_MAX_METADATA_BLOCKSIZE);
 
@@ -3489,9 +3484,9 @@ static void check_buffer_tree_ref(struct extent_buffer *eb)
         * adequately protected by the refcount, but the TREE_REF bit and
         * its corresponding reference are not. To protect against this
         * class of races, we call check_buffer_tree_ref from the codepaths
-        * which trigger io after they set eb->io_pages. Note that once io is
-        * initiated, TREE_REF can no longer be cleared, so that is the
-        * moment at which any such race is best fixed.
+        * which trigger io. Note that once io is initiated, TREE_REF can no
+        * longer be cleared, so that is the moment at which any such race is
+        * best fixed.
         */
        refs = atomic_read(&eb->refs);
        if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
@@ -4062,7 +4057,6 @@ static void extent_buffer_read_end_io(struct btrfs_bio *bbio)
        struct bio_vec *bvec;
        u32 bio_offset = 0;
 
-       atomic_inc(&eb->refs);
        eb->read_mirror = bbio->mirror_num;
 
        if (uptodate &&
@@ -4077,7 +4071,6 @@ static void extent_buffer_read_end_io(struct btrfs_bio *bbio)
        }
 
        bio_for_each_segment_all(bvec, &bbio->bio, iter_all) {
-               atomic_dec(&eb->io_pages);
                end_page_read(bvec->bv_page, uptodate, eb->start + bio_offset,
                              bvec->bv_len);
                bio_offset += bvec->bv_len;
@@ -4100,8 +4093,8 @@ static void __read_extent_buffer_pages(struct extent_buffer *eb, int mirror_num,
 
        clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
        eb->read_mirror = 0;
-       atomic_set(&eb->io_pages, num_pages);
        check_buffer_tree_ref(eb);
+       atomic_inc(&eb->refs);
 
        bbio = btrfs_bio_alloc(INLINE_EXTENT_BUFFER_PAGES,
                               REQ_OP_READ | REQ_META, eb->fs_info,

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index e11ee09ab26b6468e4432a1d08ddcd6d6bc58d2d..217c433bb9998face3d8c3e3eaf63a08b406034f 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -79,7 +79,6 @@ struct extent_buffer {
        struct btrfs_fs_info *fs_info;
        spinlock_t refs_lock;
        atomic_t refs;
-       atomic_t io_pages;
        int read_mirror;
        struct rcu_head rcu_head;
        pid_t lock_owner;