ceph: avoid carrying Fw cap during write into page cache

The generic_file_aio_write call may block on balance_dirty_pages while we
flush data to the OSDs.  If we hold a reference to the FILE_WR cap during
that interval revocation by the MDS (e.g., to do a stat(2)) may be very
slow.

Reviewed-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 19 insertions, 3 deletions

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 44e4fe9fba02..6c90cf090601 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -713,7 +713,7 @@ retry_snap:
                 want = CEPH_CAP_FILE_BUFFER;
         ret = ceph_get_caps(ci, CEPH_CAP_FILE_WR, want, &got, endoff);
         if (ret < 0)
-                goto out;
+                goto out_put;
 
         dout("aio_write %p %llx.%llx %llu~%u  got cap refs on %s\n",
              inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
@@ -726,8 +726,18 @@ retry_snap:
                 ret = ceph_sync_write(file, iov->iov_base, iov->iov_len,
                         &iocb->ki_pos);
         } else {
-                ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
+                /*
+                 * buffered write; drop Fw early to avoid slow
+                 * revocation if we get stuck on balance_dirty_pages
+                 */
+                int dirty;
+
+                spin_lock(&inode->i_lock);
+                dirty = __ceph_mark_dirty_caps(ci, CEPH_CAP_FILE_WR);
+                spin_unlock(&inode->i_lock);
+                ceph_put_cap_refs(ci, got);
 
+                ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
                 if ((ret >= 0 || ret == -EIOCBQUEUED) &&
                     ((file->f_flags & O_SYNC) || IS_SYNC(file->f_mapping->host)
                      || ceph_osdmap_flag(osdc->osdmap, CEPH_OSDMAP_NEARFULL))) {
@@ -735,7 +745,12 @@ retry_snap:
                         if (err < 0)
                                 ret = err;
                 }
+
+                if (dirty)
+                        __mark_inode_dirty(inode, dirty);
+                goto out;
         }
+
         if (ret >= 0) {
                 int dirty;
                 spin_lock(&inode->i_lock);
@@ -745,12 +760,13 @@ retry_snap:
                         __mark_inode_dirty(inode, dirty);
         }
 
-out:
+out_put:
         dout("aio_write %p %llx.%llx %llu~%u  dropping cap refs on %s\n",
              inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
              ceph_cap_string(got));
         ceph_put_cap_refs(ci, got);
 
+out:
         if (ret == -EOLDSNAPC) {
                 dout("aio_write %p %llx.%llx %llu~%u got EOLDSNAPC, retrying\n",
                      inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len);