The "dump_page_cache" seq_file currently tries to encode
a location in the hash table into a 64bit file index so that
the seq_file can seek to any location.

This is not necessary with the current implementation of seq_file.
seq_file performs any seeks needed itself by rewinding and calling
->next and ->show until the required index is reached.

The required behaviour of ->next is that it always return the next
object after the last one returned by either ->start or ->next.
It can ignore the ppos, but should increment it.

The required behaviour of ->start is one of:
1/ if *ppos is 0, then return the first object
2/ if *ppos is the same value that was passed to the most recent call
   to either ->start or ->next, then return the same object again
3/ if *ppos is anything else, return the next object after the most
   recently returned one.

To implement this we store a vvp_pgcache_id (index into hash table)
in the seq_private data structure, and also store 'prev_pos' as the
last value passed to either ->start or ->next.

We remove all converstion of an id to a pos, and any limits on the
size of the vpi_depth.

vvp_pgcache_obj_get() is changed to ignore dying objects so that
vvp_pgcache_obj only returns NULL when it reaches the end of a hash
chain, and so vpi_bucket needs to be incremented.

A reference to the current ->clob pointer is now kept as long as we
are iterating over the pages in a given object, so we don't have to
try to find it again (and possibly fail) for each page.

And the ->start and ->next functions are changed as described above.

Signed-off-by: NeilBrown <ne...@suse.com>
---
 drivers/staging/lustre/lustre/llite/vvp_dev.c |  173 +++++++++++--------------
 1 file changed, 79 insertions(+), 94 deletions(-)

diff --git a/drivers/staging/lustre/lustre/llite/vvp_dev.c 
b/drivers/staging/lustre/lustre/llite/vvp_dev.c
index 39a85e967368..64c3fdbbf0eb 100644
--- a/drivers/staging/lustre/lustre/llite/vvp_dev.c
+++ b/drivers/staging/lustre/lustre/llite/vvp_dev.c
@@ -365,22 +365,6 @@ int cl_sb_fini(struct super_block *sb)
  *
  ****************************************************************************/
 
-/*
- * To represent contents of a page cache as a byte stream, following
- * information if encoded in 64bit offset:
- *
- *       - file hash bucket in lu_site::ls_hash[]       28bits
- *
- *       - how far file is from bucket head          4bits
- *
- *       - page index                             32bits
- *
- * First two data identify a file in the cache uniquely.
- */
-
-#define PGC_OBJ_SHIFT (32 + 4)
-#define PGC_DEPTH_SHIFT (32)
-
 struct vvp_pgcache_id {
        unsigned int             vpi_bucket;
        unsigned int             vpi_depth;
@@ -395,37 +379,26 @@ struct seq_private {
        struct lu_env           *env;
        u16                     refcheck;
        struct cl_object        *clob;
+       struct vvp_pgcache_id   id;
+       /*
+        * prev_pos is the 'pos' of the last object returned
+        * by ->start of ->next.
+        */
+       loff_t                  prev_pos;
 };
 
-static void vvp_pgcache_id_unpack(loff_t pos, struct vvp_pgcache_id *id)
-{
-       BUILD_BUG_ON(sizeof(pos) != sizeof(__u64));
-
-       id->vpi_index  = pos & 0xffffffff;
-       id->vpi_depth  = (pos >> PGC_DEPTH_SHIFT) & 0xf;
-       id->vpi_bucket = (unsigned long long)pos >> PGC_OBJ_SHIFT;
-}
-
-static loff_t vvp_pgcache_id_pack(struct vvp_pgcache_id *id)
-{
-       return
-               ((__u64)id->vpi_index) |
-               ((__u64)id->vpi_depth  << PGC_DEPTH_SHIFT) |
-               ((__u64)id->vpi_bucket << PGC_OBJ_SHIFT);
-}
-
 static int vvp_pgcache_obj_get(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                               struct hlist_node *hnode, void *data)
 {
        struct vvp_pgcache_id   *id  = data;
        struct lu_object_header *hdr = cfs_hash_object(hs, hnode);
 
+       if (lu_object_is_dying(hdr))
+               return 0;
+
        if (id->vpi_curdep-- > 0)
                return 0; /* continue */
 
-       if (lu_object_is_dying(hdr))
-               return 1;
-
        cfs_hash_get(hs, hnode);
        id->vpi_obj = hdr;
        return 1;
@@ -437,7 +410,6 @@ static struct cl_object *vvp_pgcache_obj(const struct 
lu_env *env,
 {
        LASSERT(lu_device_is_cl(dev));
 
-       id->vpi_depth &= 0xf;
        id->vpi_obj    = NULL;
        id->vpi_curdep = id->vpi_depth;
 
@@ -452,55 +424,42 @@ static struct cl_object *vvp_pgcache_obj(const struct 
lu_env *env,
                        return lu2cl(lu_obj);
                }
                lu_object_put(env, lu_object_top(id->vpi_obj));
-
-       } else if (id->vpi_curdep > 0) {
-               id->vpi_depth = 0xf;
        }
        return NULL;
 }
 
-static struct page *vvp_pgcache_find(const struct lu_env *env,
-                                    struct lu_device *dev,
-                                    struct cl_object **clobp, loff_t *pos)
+static struct page *vvp_pgcache_current(struct seq_private *priv)
 {
-       struct cl_object     *clob;
-       struct lu_site       *site;
-       struct vvp_pgcache_id id;
-
-       site = dev->ld_site;
-       vvp_pgcache_id_unpack(*pos, &id);
-
-       while (1) {
-               if (id.vpi_bucket >= CFS_HASH_NHLIST(site->ls_obj_hash))
-                       return NULL;
-               clob = vvp_pgcache_obj(env, dev, &id);
-               if (clob) {
-                       struct inode *inode = vvp_object_inode(clob);
-                       struct page *vmpage;
-                       int nr;
-
-                       nr = find_get_pages_contig(inode->i_mapping,
-                                                  id.vpi_index, 1, &vmpage);
-                       if (nr > 0) {
-                               id.vpi_index = vmpage->index;
-                               /* Cant support over 16T file */
-                               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);
+       struct lu_device *dev = &priv->sbi->ll_cl->cd_lu_dev;
+
+       while(1) {
+               struct inode *inode;
+               int nr;
+               struct page *vmpage;
+
+               if (!priv->clob) {
+                       struct cl_object *clob;
+
+                       while ((clob = vvp_pgcache_obj(priv->env, dev, 
&priv->id)) == NULL &&
+                              ++(priv->id.vpi_bucket) < 
CFS_HASH_NHLIST(dev->ld_site->ls_obj_hash))
+                               priv->id.vpi_depth = 0;
+                       if (!clob)
+                               return NULL;
+                       priv->clob = clob;
+                       priv->id.vpi_index = 0;
+               }
+
+               inode = vvp_object_inode(priv->clob);
+               nr = find_get_pages_contig(inode->i_mapping, 
priv->id.vpi_index, 1, &vmpage);
+               if (nr > 0) {
+                       priv->id.vpi_index = vmpage->index;
+                       return vmpage;
                }
-               /* to the next object. */
-               ++id.vpi_depth;
-               id.vpi_depth &= 0xf;
-               if (id.vpi_depth == 0 && ++id.vpi_bucket == 0)
-                       return NULL;
-               id.vpi_index = 0;
+               lu_object_ref_del(&priv->clob->co_lu, "dump", current);
+               cl_object_put(priv->env, priv->clob);
+               priv->clob = NULL;
+               priv->id.vpi_index = 0;
+               priv->id.vpi_depth++;
        }
 }
 
@@ -558,36 +517,54 @@ static int vvp_pgcache_show(struct seq_file *f, void *v)
        } else {
                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_rewind(struct seq_private *priv)
+{
+       if (priv->prev_pos) {
+               memset(&priv->id, 0, sizeof(priv->id));
+               priv->prev_pos = 0;
+               if (priv->clob) {
+                       lu_object_ref_del(&priv->clob->co_lu, "dump", current);
+                       cl_object_put(priv->env, priv->clob);
+               }
+               priv->clob = NULL;
+       }
+}
+
+static struct page *vvp_pgcache_next_page(struct seq_private *priv)
+{
+       priv->id.vpi_index += 1;
+       return vvp_pgcache_current(priv);
+}
+
 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)
-               ret = ERR_PTR(-EFBIG);
-       else
-               ret = vvp_pgcache_find(priv->env, &priv->sbi->ll_cl->cd_lu_dev,
-                                      &priv->clob, pos);
+       if (*pos == 0)
+               vvp_pgcache_rewind(priv);
+       else if (*pos == priv->prev_pos)
+               /* Return the current item */;
+       else {
+               WARN_ON(*pos != priv->prev_pos + 1);
+               priv->id.vpi_index += 1;
+       }
 
-       return ret;
+       priv->prev_pos = *pos;
+       return vvp_pgcache_current(priv);
 }
 
 static void *vvp_pgcache_next(struct seq_file *f, void *v, loff_t *pos)
 {
        struct seq_private *priv = f->private;
-       struct page *ret;
 
+       WARN_ON(*pos != priv->prev_pos);
        *pos += 1;
-       ret = vvp_pgcache_find(priv->env, &priv->sbi->ll_cl->cd_lu_dev,
-                              &priv->clob, pos);
-       return ret;
+       priv->prev_pos = *pos;
+       return vvp_pgcache_next_page(priv);
 }
 
 static void vvp_pgcache_stop(struct seq_file *f, void *v)
@@ -612,6 +589,9 @@ static int vvp_dump_pgcache_seq_open(struct inode *inode, 
struct file *filp)
 
        priv->sbi = inode->i_private;
        priv->env = cl_env_get(&priv->refcheck);
+       priv->clob = NULL;
+       memset(&priv->id, 0, sizeof(priv->id));
+
        if (IS_ERR(priv->env)) {
                int err = PTR_ERR(priv->env);
                seq_release_private(inode, filp);
@@ -625,6 +605,11 @@ static int vvp_dump_pgcache_seq_release(struct inode 
*inode, struct file *file)
        struct seq_file *seq = file->private_data;
        struct seq_private *priv = seq->private;
 
+       if (priv->clob) {
+               lu_object_ref_del(&priv->clob->co_lu, "dump", current);
+               cl_object_put(priv->env, priv->clob);
+       }
+
        cl_env_put(priv->env, &priv->refcheck);
        return seq_release_private(inode, file);
 }


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