gfs2: Extended attribute readahead optimization

Instead of submitting a READ_SYNC bio for the inode and a READA bio for
the inode's extended attributes through submit_bh, submit a single READ_SYNC
bio for both through submit_bio when possible.  This can be more
efficient on some kinds of block devices.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 0f24828f8488c4fbfebd9886b028aee7281d7c11..e137d96f1b17bc1e4250bb0153109be757660c86 100644 (file)
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -187,19 +187,50 @@ struct buffer_head *gfs2_meta_new(struct gfs2_glock *gl, u64 blkno)
        return bh;
 }
 
-static void gfs2_meta_readahead(struct gfs2_glock *gl, u64 blkno)
+static void gfs2_meta_read_endio(struct bio *bio)
 {
-       struct buffer_head *bh;
+       struct bio_vec *bvec;
+       int i;
+
+       bio_for_each_segment_all(bvec, bio, i) {
+               struct page *page = bvec->bv_page;
+               struct buffer_head *bh = page_buffers(page);
+               unsigned int len = bvec->bv_len;
+
+               while (bh_offset(bh) < bvec->bv_offset)
+                       bh = bh->b_this_page;
+               do {
+                       struct buffer_head *next = bh->b_this_page;
+                       len -= bh->b_size;
+                       bh->b_end_io(bh, !bio->bi_error);
+                       bh = next;
+               } while (bh && len);
+       }
+       bio_put(bio);
+}
 
-       bh = gfs2_getbuf(gl, blkno, 1);
-       lock_buffer(bh);
-       if (buffer_uptodate(bh)) {
-               unlock_buffer(bh);
-               brelse(bh);
+/*
+ * Submit several consecutive buffer head I/O requests as a single bio I/O
+ * request.  (See submit_bh_wbc.)
+ */
+static void gfs2_submit_bhs(int rw, struct buffer_head *bhs[], int num)
+{
+       struct buffer_head *bh = bhs[0];
+       struct bio *bio;
+       int i;
+
+       if (!num)
                return;
+
+       bio = bio_alloc(GFP_NOIO, num);
+       bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
+       bio->bi_bdev = bh->b_bdev;
+       for (i = 0; i < num; i++) {
+               bh = bhs[i];
+               bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
        }
-       bh->b_end_io = end_buffer_read_sync;
-       submit_bh(READA | REQ_META | REQ_PRIO, bh);
+       bio->bi_end_io = gfs2_meta_read_endio;
+       submit_bio(rw, bio);
 }
 
 /**
@@ -216,7 +247,8 @@ int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
                   int rahead, struct buffer_head **bhp)
 {
        struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
-       struct buffer_head *bh;
+       struct buffer_head *bh, *bhs[2];
+       int num = 0;
 
        if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) {
                *bhp = NULL;
@@ -228,18 +260,31 @@ int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
        lock_buffer(bh);
        if (buffer_uptodate(bh)) {
                unlock_buffer(bh);
-               if (rahead)
-                       gfs2_meta_readahead(gl, blkno + 1);
-               return 0;
+               flags &= ~DIO_WAIT;
+       } else {
+               bh->b_end_io = end_buffer_read_sync;
+               get_bh(bh);
+               bhs[num++] = bh;
        }
-       bh->b_end_io = end_buffer_read_sync;
-       get_bh(bh);
-       submit_bh(READ_SYNC | REQ_META | REQ_PRIO, bh);
-       if (rahead)
-               gfs2_meta_readahead(gl, blkno + 1);
+
+       if (rahead) {
+               bh = gfs2_getbuf(gl, blkno + 1, CREATE);
+
+               lock_buffer(bh);
+               if (buffer_uptodate(bh)) {
+                       unlock_buffer(bh);
+                       brelse(bh);
+               } else {
+                       bh->b_end_io = end_buffer_read_sync;
+                       bhs[num++] = bh;
+               }
+       }
+
+       gfs2_submit_bhs(READ_SYNC | REQ_META | REQ_PRIO, bhs, num);
        if (!(flags & DIO_WAIT))
                return 0;
 
+       bh = *bhp;
        wait_on_buffer(bh);
        if (unlikely(!buffer_uptodate(bh))) {
                struct gfs2_trans *tr = current->journal_info;