staging: lustre: llite: remove redundant lookup in dump_pgcache

Both the 'next' and the 'show' functions for the dump_page_cache
seqfile perform a lookup based on the current file index.  This is
needless duplication.

The reason appears to be that the state that needs to be communicated
from "next" to "show" is two pointers, but seq_file only provides for
a single pointer to be returned from next and passed to show.

So make use of the new 'seq_private' structure to store the extra
pointer.
So when 'next' (or 'start') find something, it returns the page and
stores the clob in the private area.
'show' accepts the page as an argument, and finds the clob where it
was stored.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/vvp_dev.c

@@ -394,6 +394,7 @@ struct seq_private {
 	struct ll_sb_info	*sbi;
 	struct lu_env		*env;
 	u16			refcheck;
+	struct cl_object	*clob;
 };
 
 static void vvp_pgcache_id_unpack(loff_t pos, struct vvp_pgcache_id *id)
@@ -458,19 +459,20 @@ static struct cl_object *vvp_pgcache_obj(const struct lu_env *env,
 	return NULL;
 }
 
-static loff_t vvp_pgcache_find(const struct lu_env *env,
-			       struct lu_device *dev, loff_t pos)
+static struct page *vvp_pgcache_find(const struct lu_env *env,
+				     struct lu_device *dev,
+				     struct cl_object **clobp, loff_t *pos)
 {
 	struct cl_object     *clob;
 	struct lu_site       *site;
 	struct vvp_pgcache_id id;
 
 	site = dev->ld_site;
-	vvp_pgcache_id_unpack(pos, &id);
+	vvp_pgcache_id_unpack(*pos, &id);
 
 	while (1) {
 		if (id.vpi_bucket >= CFS_HASH_NHLIST(site->ls_obj_hash))
-			return ~0ULL;
+			return NULL;
 		clob = vvp_pgcache_obj(env, dev, &id);
 		if (clob) {
 			struct inode *inode = vvp_object_inode(clob);
@@ -482,20 +484,22 @@ static loff_t vvp_pgcache_find(const struct lu_env *env,
 			if (nr > 0) {
 				id.vpi_index = vmpage->index;
 				/* Cant support over 16T file */
-				nr = !(vmpage->index > 0xffffffff);
+				if (vmpage->index <= 0xffffffff) {
+					*clobp = clob;
+					*pos = vvp_pgcache_id_pack(&id);
+					return vmpage;
+				}
 				put_page(vmpage);
 			}
 
 			lu_object_ref_del(&clob->co_lu, "dump", current);
 			cl_object_put(env, clob);
-			if (nr > 0)
-				return vvp_pgcache_id_pack(&id);
 		}
 		/* to the next object. */
 		++id.vpi_depth;
 		id.vpi_depth &= 0xf;
 		if (id.vpi_depth == 0 && ++id.vpi_bucket == 0)
-			return ~0ULL;
+			return NULL;
 		id.vpi_index = 0;
 	}
 }
@@ -538,72 +542,52 @@ static void vvp_pgcache_page_show(const struct lu_env *env,
 static int vvp_pgcache_show(struct seq_file *f, void *v)
 {
 	struct seq_private	*priv = f->private;
-	loff_t		   pos;
-	struct cl_object	*clob;
-	struct vvp_pgcache_id    id;
-
-	pos = *(loff_t *)v;
-	vvp_pgcache_id_unpack(pos, &id);
-	clob = vvp_pgcache_obj(priv->env, &priv->sbi->ll_cl->cd_lu_dev, &id);
-	if (clob) {
-		struct inode *inode = vvp_object_inode(clob);
-		struct cl_page *page = NULL;
-		struct page *vmpage;
-		int result;
-
-		result = find_get_pages_contig(inode->i_mapping,
-					       id.vpi_index, 1,
-					       &vmpage);
-		if (result > 0) {
-			lock_page(vmpage);
-			page = cl_vmpage_page(vmpage, clob);
-			unlock_page(vmpage);
-			put_page(vmpage);
-		}
-
-		seq_printf(f, "%8x@" DFID ": ", id.vpi_index,
-			   PFID(lu_object_fid(&clob->co_lu)));
-		if (page) {
-			vvp_pgcache_page_show(priv->env, f, page);
-			cl_page_put(priv->env, page);
-		} else {
-			seq_puts(f, "missing\n");
-		}
-		lu_object_ref_del(&clob->co_lu, "dump", current);
-		cl_object_put(priv->env, clob);
+	struct page		*vmpage = v;
+	struct cl_page		*page;
+
+	seq_printf(f, "%8lx@" DFID ": ", vmpage->index,
+		   PFID(lu_object_fid(&priv->clob->co_lu)));
+	lock_page(vmpage);
+	page = cl_vmpage_page(vmpage, priv->clob);
+	unlock_page(vmpage);
+	put_page(vmpage);
+
+	if (page) {
+		vvp_pgcache_page_show(priv->env, f, page);
+		cl_page_put(priv->env, page);
 	} else {
-		seq_printf(f, "%llx missing\n", pos);
+		seq_puts(f, "missing\n");
 	}
+	lu_object_ref_del(&priv->clob->co_lu, "dump", current);
+	cl_object_put(priv->env, priv->clob);
+
 	return 0;
 }
 
 static void *vvp_pgcache_start(struct seq_file *f, loff_t *pos)
 {
 	struct seq_private	*priv = f->private;
+	struct page *ret;
 
 	if (priv->sbi->ll_site->ls_obj_hash->hs_cur_bits >
-	    64 - PGC_OBJ_SHIFT) {
-		pos = ERR_PTR(-EFBIG);
-	} else {
-		*pos = vvp_pgcache_find(priv->env, &priv->sbi->ll_cl->cd_lu_dev,
-					*pos);
-		if (*pos == ~0ULL)
-			pos = NULL;
-	}
+	    64 - PGC_OBJ_SHIFT)
+		ret = ERR_PTR(-EFBIG);
+	else
+		ret = vvp_pgcache_find(priv->env, &priv->sbi->ll_cl->cd_lu_dev,
+				       &priv->clob, pos);
 
-	return pos;
+	return ret;
 }
 
 static void *vvp_pgcache_next(struct seq_file *f, void *v, loff_t *pos)
 {
 	struct seq_private *priv = f->private;
+	struct page *ret;
 
-	*pos = vvp_pgcache_find(priv->env, &priv->sbi->ll_cl->cd_lu_dev,
-				*pos + 1);
-	if (*pos == ~0ULL)
-		pos = NULL;
-
-	return pos;
+	*pos += 1;
+	ret = vvp_pgcache_find(priv->env, &priv->sbi->ll_cl->cd_lu_dev,
+			       &priv->clob, pos);
+	return ret;
 }
 
 static void vvp_pgcache_stop(struct seq_file *f, void *v)