gfs2: Avoid unnecessary transactions in evict_linked_inode

In evict_linked_inode(), the truncate_inode_pages() calls are carried
out inside a transaction.  This code was added to what was then function
gfs2_delete_inode() in commit 16615be ("[GFS2] Clean up journaled
data writing").

These transactions are only used for creating revokes for the jdata
buffers in the journal, so don't create such transactions when we know
that the address space doesn't contain any jdata buffers for this inode
and truncate the metadata address space outside of the transaction.

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

Author: Andreas Gruenbacher

fs/gfs2/super.c

@@ -1324,6 +1324,35 @@ static int evict_unlinked_inode(struct inode *inode)
 	return ret;
 }
 
+static int gfs2_truncate_inode_pages(struct inode *inode)
+{
+	struct gfs2_inode *ip = GFS2_I(inode);
+	struct gfs2_sbd *sdp = GFS2_SB(inode);
+	struct address_space *mapping = &inode->i_data;
+	bool need_trans = gfs2_is_jdata(ip) && mapping->nrpages;
+	int ret;
+
+	/*
+	 * Truncating a jdata inode address space may create revokes in
+	 * truncate_inode_pages() -> gfs2_invalidate_folio() -> ... ->
+	 * gfs2_remove_from_journal(), so we need a transaction here.
+	 *
+	 * FIXME: During a withdraw, no new transactions can be created.
+	 * In that case, we skip the truncate, but that doesn't help because
+	 * truncate_inode_pages_final() will then call gfs2_invalidate_folio()
+	 * again, and outside of a transaction.
+	 */
+	if (need_trans) {
+		ret = gfs2_trans_begin(sdp, 0, sdp->sd_jdesc->jd_blocks);
+		if (ret)
+			return ret;
+	}
+	truncate_inode_pages(mapping, 0);
+	if (need_trans)
+		gfs2_trans_end(sdp);
+	return 0;
+}
+
 /*
  * evict_linked_inode - evict an inode whose dinode has not been unlinked
  * @inode: The inode to evict
@@ -1346,14 +1375,10 @@ static int evict_linked_inode(struct inode *inode)
 	write_inode_now(inode, 1);
 	gfs2_ail_flush(ip->i_gl, 0);
 
-	ret = gfs2_trans_begin(sdp, 0, sdp->sd_jdesc->jd_blocks);
+	ret = gfs2_truncate_inode_pages(inode);
 	if (ret)
 		return ret;
-
-	/* Needs to be done before glock release & also in a transaction */
-	truncate_inode_pages(&inode->i_data, 0);
 	truncate_inode_pages(metamapping, 0);
-	gfs2_trans_end(sdp);
 	return 0;
 }