[lustre-devel] [PATCH 18/20] staging: lustre: change how "dump_page_cache" walks a hash table
NeilBrown
neilb at suse.com
Wed Apr 11 14:54:49 PDT 2018
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 <neilb at 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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