gfs2: Stop using glock holder auto-demotion for now

We're having unresolved issues with the glock holder auto-demotion mechanism
introduced in commit edd7c63bdb86.  This mechanism was assumed to be essential
for avoiding frequent short reads and writes until commit 5d328f8bc513
("gfs2: No short reads or writes upon glock contention").  Since then,
when the inode glock is lost, it is simply re-acquired and the operation
is resumed.  This means that apart from the performance penalty, we
might as well drop the inode glock before faulting in pages, and
re-acquire it afterwards.

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

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 5eda1bcc85e379e7f9aab5b031523df3aa4a8e2d..2556ae1f92ea2d9e27d0fefe9c60c09543c6c563 100644 (file)
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -832,7 +832,6 @@ retry:
        ret = gfs2_glock_nq(gh);
        if (ret)
                goto out_uninit;
-retry_under_glock:
        pagefault_disable();
        to->nofault = true;
        ret = iomap_dio_rw(iocb, to, &gfs2_iomap_ops, NULL,
@@ -845,14 +844,10 @@ retry_under_glock:
                read = ret;
 
        if (should_fault_in_pages(to, iocb, &prev_count, &window_size)) {
-               gfs2_holder_allow_demote(gh);
+               gfs2_glock_dq(gh);
                window_size -= fault_in_iov_iter_writeable(to, window_size);
-               gfs2_holder_disallow_demote(gh);
-               if (window_size) {
-                       if (gfs2_holder_queued(gh))
-                               goto retry_under_glock;
+               if (window_size)
                        goto retry;
-               }
        }
 out_unlock:
        if (gfs2_holder_queued(gh))
@@ -900,7 +895,6 @@ retry:
        /* Silently fall back to buffered I/O when writing beyond EOF */
        if (iocb->ki_pos + iov_iter_count(from) > i_size_read(&ip->i_inode))
                goto out_unlock;
-retry_under_glock:
 
        from->nofault = true;
        ret = iomap_dio_rw(iocb, from, &gfs2_iomap_ops, NULL,
@@ -916,14 +910,10 @@ retry_under_glock:
                written = ret;
 
        if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
-               gfs2_holder_allow_demote(gh);
+               gfs2_glock_dq(gh);
                window_size -= fault_in_iov_iter_readable(from, window_size);
-               gfs2_holder_disallow_demote(gh);
-               if (window_size) {
-                       if (gfs2_holder_queued(gh))
-                               goto retry_under_glock;
+               if (window_size)
                        goto retry;
-               }
        }
 out_unlock:
        if (gfs2_holder_queued(gh))
@@ -974,7 +964,6 @@ retry:
        ret = gfs2_glock_nq(&gh);
        if (ret)
                goto out_uninit;
-retry_under_glock:
        pagefault_disable();
        ret = generic_file_read_iter(iocb, to);
        pagefault_enable();
@@ -984,14 +973,10 @@ retry_under_glock:
                read += ret;
 
        if (should_fault_in_pages(to, iocb, &prev_count, &window_size)) {
-               gfs2_holder_allow_demote(&gh);
+               gfs2_glock_dq(&gh);
                window_size -= fault_in_iov_iter_writeable(to, window_size);
-               gfs2_holder_disallow_demote(&gh);
-               if (window_size) {
-                       if (gfs2_holder_queued(&gh))
-                               goto retry_under_glock;
+               if (window_size)
                        goto retry;
-               }
        }
 out_unlock:
        if (gfs2_holder_queued(&gh))
@@ -1030,22 +1015,17 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb,
 
        gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, gh);
 retry:
-       ret = gfs2_glock_nq(gh);
-       if (ret)
-               goto out_uninit;
        if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
-retry_under_glock:
-               gfs2_holder_allow_demote(gh);
                window_size -= fault_in_iov_iter_readable(from, window_size);
-               gfs2_holder_disallow_demote(gh);
                if (!window_size) {
                        ret = -EFAULT;
-                       goto out_unlock;
+                       goto out_uninit;
                }
-               if (!gfs2_holder_queued(gh))
-                       goto retry;
                from->count = min(from->count, window_size);
        }
+       ret = gfs2_glock_nq(gh);
+       if (ret)
+               goto out_uninit;
 
        if (inode == sdp->sd_rindex) {
                struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
@@ -1073,8 +1053,10 @@ retry_under_glock:
                goto out_unlock;
 
        from->count = orig_count - written;
-       if (should_fault_in_pages(from, iocb, &prev_count, &window_size))
-               goto retry_under_glock;
+       if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
+               gfs2_glock_dq(gh);
+               goto retry;
+       }
 out_unlock:
        if (gfs2_holder_queued(gh))
                gfs2_glock_dq(gh);