staging: lustre: statahead: use dcache-like interface for sa entry
authorLai Siyao <lai.siyao@intel.com>
Sun, 18 Sep 2016 20:37:55 +0000 (16:37 -0400)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Mon, 19 Sep 2016 07:44:03 +0000 (09:44 +0200)
Rename ll_sa_entry to sa_entry, and manage sa_entry cache with
dcache-like interfaces.

sa_entry is not needed to be refcounted, because only scanner
can free it, so after it's put in stat list, statahead thread
shouldn't access it any longer.

ll_statahead_interpret() doesn't need to take sai refcount,
because statahead thread will wait for all inflight RPC to
finish.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3270
Reviewed-on: http://review.whamcloud.com/9664
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/staging/lustre/lustre/include/obd.h
drivers/staging/lustre/lustre/llite/llite_internal.h
drivers/staging/lustre/lustre/llite/statahead.c

index 1c884c00d6f76e7e4e20b2cfdd9615abb2192b56..6758bf4f7b9c5d50b9f4ac4a5256fe6a37e680dd 100644 (file)
@@ -812,7 +812,7 @@ struct md_enqueue_info {
        struct inode       *mi_dir;
        int (*mi_cb)(struct ptlrpc_request *req,
                     struct md_enqueue_info *minfo, int rc);
-       __u64              mi_cbdata;
+       void                    *mi_cbdata;
 };
 
 struct obd_ops {
index 9a9fefd18591423537fc1483a58a2a9326daa71c..cd639f48ba04fe683aca13cba530aa5f0c4d49b8 100644 (file)
@@ -1131,10 +1131,12 @@ struct ll_statahead_info {
        wait_queue_head_t       sai_waitq;      /* stat-ahead wait queue */
        struct ptlrpc_thread    sai_thread;     /* stat-ahead thread */
        struct ptlrpc_thread    sai_agl_thread; /* AGL thread */
-       struct list_head        sai_entries;    /* entry list */
-       struct list_head        sai_entries_received; /* entries returned */
-       struct list_head        sai_entries_stated;   /* entries stated */
-       struct list_head        sai_entries_agl; /* AGL entries to be sent */
+       struct list_head        sai_interim_entries; /* entries which got async
+                                                     * stat reply, but not
+                                                     * instantiated
+                                                     */
+       struct list_head        sai_entries;    /* completed entries */
+       struct list_head        sai_agls;       /* AGLs to be sent */
        struct list_head        sai_cache[LL_SA_CACHE_SIZE];
        spinlock_t              sai_cache_lock[LL_SA_CACHE_SIZE];
        atomic_t                sai_cache_count; /* entry count in cache */
index 5760974e88c54dca976954057bf630aa6f930505..0d87dc91a72ca1295c51e3da22bb660aa7375a13 100644 (file)
@@ -49,24 +49,26 @@ enum se_stat {
        SA_ENTRY_INIT = 0,      /** init entry */
        SA_ENTRY_SUCC = 1,      /** stat succeed */
        SA_ENTRY_INVA = 2,      /** invalid entry */
-       SA_ENTRY_DEST = 3,      /** entry to be destroyed */
 };
 
-struct ll_sa_entry {
-       /* link into sai->sai_entries */
-       struct list_head              se_link;
-       /* link into sai->sai_entries_{received,stated} */
+/*
+ * sa_entry is not refcounted: statahead thread allocates it and do async stat,
+ * and in async stat callback ll_statahead_interpret() will add it into
+ * sai_cb_entries, later statahead thread will call sa_handle_callback() to
+ * instantiate entry and move it into sai_entries, and then only scanner process
+ * can access and free it.
+ */
+struct sa_entry {
+       /* link into sai_cb_entries or sai_entries */
        struct list_head              se_list;
        /* link into sai hash table locally */
        struct list_head              se_hash;
-       /* entry reference count */
-       atomic_t            se_refcount;
        /* entry index in the sai */
        __u64              se_index;
        /* low layer ldlm lock handle */
        __u64              se_handle;
        /* entry status */
-       enum se_stat       se_stat;
+       enum se_stat            se_state;
        /* entry size, contains name */
        int                  se_size;
        /* pointer to async getattr enqueue info */
@@ -85,13 +87,13 @@ static DEFINE_SPINLOCK(sai_generation_lock);
 /*
  * The entry only can be released by the caller, it is necessary to hold lock.
  */
-static inline int ll_sa_entry_stated(struct ll_sa_entry *entry)
+static inline int sa_ready(struct sa_entry *entry)
 {
        smp_rmb();
-       return (entry->se_stat != SA_ENTRY_INIT);
+       return (entry->se_state != SA_ENTRY_INIT);
 }
 
-static inline int ll_sa_entry_hash(int val)
+static inline int sa_hash(int val)
 {
        return val & LL_SA_CACHE_MASK;
 }
@@ -100,9 +102,9 @@ static inline int ll_sa_entry_hash(int val)
  * Insert entry to hash SA table.
  */
 static inline void
-ll_sa_entry_enhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_rehash(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-       int i = ll_sa_entry_hash(entry->se_qstr.hash);
+       int i = sa_hash(entry->se_qstr.hash);
 
        spin_lock(&sai->sai_cache_lock[i]);
        list_add_tail(&entry->se_hash, &sai->sai_cache[i]);
@@ -113,9 +115,9 @@ ll_sa_entry_enhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
  * Remove entry from SA table.
  */
 static inline void
-ll_sa_entry_unhash(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_unhash(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-       int i = ll_sa_entry_hash(entry->se_qstr.hash);
+       int i = sa_hash(entry->se_qstr.hash);
 
        spin_lock(&sai->sai_cache_lock[i]);
        list_del_init(&entry->se_hash);
@@ -133,14 +135,14 @@ static inline int sa_sent_full(struct ll_statahead_info *sai)
        return atomic_read(&sai->sai_cache_count) >= sai->sai_max;
 }
 
-static inline int sa_received_empty(struct ll_statahead_info *sai)
+static inline int sa_has_callback(struct ll_statahead_info *sai)
 {
-       return list_empty(&sai->sai_entries_received);
+       return !list_empty(&sai->sai_interim_entries);
 }
 
 static inline int agl_list_empty(struct ll_statahead_info *sai)
 {
-       return list_empty(&sai->sai_entries_agl);
+       return list_empty(&sai->sai_agls);
 }
 
 /**
@@ -168,17 +170,16 @@ static inline int is_omitted_entry(struct ll_statahead_info *sai, __u64 index)
 /*
  * Insert it into sai_entries tail when init.
  */
-static struct ll_sa_entry *
-ll_sa_entry_alloc(struct dentry *parent,
-                 struct ll_statahead_info *sai, __u64 index,
-                 const char *name, int len)
+static struct sa_entry *
+sa_alloc(struct dentry *parent, struct ll_statahead_info *sai, __u64 index,
+        const char *name, int len)
 {
        struct ll_inode_info *lli;
-       struct ll_sa_entry   *entry;
+       struct sa_entry   *entry;
        int                entry_size;
        char             *dname;
 
-       entry_size = sizeof(struct ll_sa_entry) + (len & ~3) + 4;
+       entry_size = sizeof(struct sa_entry) + (len & ~3) + 4;
        entry = kzalloc(entry_size, GFP_NOFS);
        if (unlikely(!entry))
                return ERR_PTR(-ENOMEM);
@@ -187,34 +188,9 @@ ll_sa_entry_alloc(struct dentry *parent,
               len, name, entry, index);
 
        entry->se_index = index;
-
-       /*
-        * Statahead entry reference rules:
-        *
-        * 1) When statahead entry is initialized, its reference is set as 2.
-        *    One reference is used by the directory scanner. When the scanner
-        *    searches the statahead cache for the given name, it can perform
-        *    lockless hash lookup (only the scanner can remove entry from hash
-        *    list), and once found, it needn't to call "atomic_inc()" for the
-        *    entry reference. So the performance is improved. After using the
-        *    statahead entry, the scanner will call "atomic_dec()" to drop the
-        *    reference held when initialization. If it is the last reference,
-        *    the statahead entry will be freed.
-        *
-        * 2) All other threads, including statahead thread and ptlrpcd thread,
-        *    when they process the statahead entry, the reference for target
-        *    should be held to guarantee the entry will not be released by the
-        *    directory scanner. After processing the entry, these threads will
-        *    drop the entry reference. If it is the last reference, the entry
-        *    will be freed.
-        *
-        *    The second reference when initializes the statahead entry is used
-        *    by the statahead thread, following the rule 2).
-        */
-       atomic_set(&entry->se_refcount, 2);
-       entry->se_stat = SA_ENTRY_INIT;
+       entry->se_state = SA_ENTRY_INIT;
        entry->se_size = entry_size;
-       dname = (char *)entry + sizeof(struct ll_sa_entry);
+       dname = (char *)entry + sizeof(struct sa_entry);
        memcpy(dname, name, len);
        dname[len] = 0;
 
@@ -224,9 +200,8 @@ ll_sa_entry_alloc(struct dentry *parent,
 
        lli = ll_i2info(sai->sai_inode);
        spin_lock(&lli->lli_sa_lock);
-       list_add_tail(&entry->se_link, &sai->sai_entries);
        INIT_LIST_HEAD(&entry->se_list);
-       ll_sa_entry_enhash(sai, entry);
+       sa_rehash(sai, entry);
        spin_unlock(&lli->lli_sa_lock);
 
        atomic_inc(&sai->sai_cache_count);
@@ -234,151 +209,130 @@ ll_sa_entry_alloc(struct dentry *parent,
        return entry;
 }
 
-/*
- * Used by the directory scanner to search entry with name.
- *
- * Only the caller can remove the entry from hash, so it is unnecessary to hold
- * hash lock. It is caller's duty to release the init refcount on the entry, so
- * it is also unnecessary to increase refcount on the entry.
- */
-static struct ll_sa_entry *
-ll_sa_entry_get_byname(struct ll_statahead_info *sai, const struct qstr *qstr)
+/* free sa_entry, which should have been unhashed and not in any list */
+static void sa_free(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-       struct ll_sa_entry *entry;
-       int i = ll_sa_entry_hash(qstr->hash);
+       CDEBUG(D_READA, "free sa entry %.*s(%p) index %llu\n",
+              entry->se_qstr.len, entry->se_qstr.name, entry,
+              entry->se_index);
 
-       list_for_each_entry(entry, &sai->sai_cache[i], se_hash) {
-               if (entry->se_qstr.hash == qstr->hash &&
-                   entry->se_qstr.len == qstr->len &&
-                   memcmp(entry->se_qstr.name, qstr->name, qstr->len) == 0)
-                       return entry;
-       }
-       return NULL;
+       LASSERT(list_empty(&entry->se_list));
+       LASSERT(list_empty(&entry->se_hash));
+
+       kfree(entry);
+       atomic_dec(&sai->sai_cache_count);
 }
 
 /*
- * Used by the async getattr request callback to find entry with index.
- *
- * Inside lli_sa_lock to prevent others to change the list during the search.
- * It needs to increase entry refcount before returning to guarantee that the
- * entry cannot be freed by others.
+ * find sa_entry by name, used by directory scanner, lock is not needed because
+ * only scanner can remove the entry from cache.
  */
-static struct ll_sa_entry *
-ll_sa_entry_get_byindex(struct ll_statahead_info *sai, __u64 index)
+static struct sa_entry *
+sa_get(struct ll_statahead_info *sai, const struct qstr *qstr)
 {
-       struct ll_sa_entry *entry;
+       struct sa_entry *entry;
+       int i = sa_hash(qstr->hash);
 
-       list_for_each_entry(entry, &sai->sai_entries, se_link) {
-               if (entry->se_index == index) {
-                       LASSERT(atomic_read(&entry->se_refcount) > 0);
-                       atomic_inc(&entry->se_refcount);
+       list_for_each_entry(entry, &sai->sai_cache[i], se_hash) {
+               if (entry->se_qstr.hash == qstr->hash &&
+                   entry->se_qstr.len == qstr->len &&
+                   memcmp(entry->se_qstr.name, qstr->name, qstr->len) == 0)
                        return entry;
-               }
-               if (entry->se_index > index)
-                       break;
        }
        return NULL;
 }
 
-static void ll_sa_entry_put(struct ll_statahead_info *sai,
-                           struct ll_sa_entry *entry)
-{
-       if (atomic_dec_and_test(&entry->se_refcount)) {
-               CDEBUG(D_READA, "free sa entry %.*s(%p) index %llu\n",
-                      entry->se_qstr.len, entry->se_qstr.name, entry,
-                      entry->se_index);
-
-               LASSERT(list_empty(&entry->se_link));
-               LASSERT(list_empty(&entry->se_list));
-               LASSERT(list_empty(&entry->se_hash));
-
-               iput(entry->se_inode);
-
-               kfree(entry);
-               atomic_dec(&sai->sai_cache_count);
-       }
-}
-
+/* unhash and unlink sa_entry, and then free it */
 static inline void
-do_sa_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_kill(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
 
        LASSERT(!list_empty(&entry->se_hash));
-       LASSERT(!list_empty(&entry->se_link));
+       LASSERT(!list_empty(&entry->se_list));
+       LASSERT(sa_ready(entry));
 
-       ll_sa_entry_unhash(sai, entry);
+       sa_unhash(sai, entry);
 
        spin_lock(&lli->lli_sa_lock);
-       entry->se_stat = SA_ENTRY_DEST;
-       list_del_init(&entry->se_link);
-       if (likely(!list_empty(&entry->se_list)))
-               list_del_init(&entry->se_list);
+       list_del_init(&entry->se_list);
        spin_unlock(&lli->lli_sa_lock);
 
-       ll_sa_entry_put(sai, entry);
+       if (entry->se_inode)
+               iput(entry->se_inode);
+
+       sa_free(sai, entry);
 }
 
-/*
- * Delete it from sai_entries_stated list when fini.
- */
+/* called by scanner after use, sa_entry will be killed */
 static void
-ll_sa_entry_fini(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
+sa_put(struct ll_statahead_info *sai, struct sa_entry *entry)
 {
-       struct ll_sa_entry *pos, *next;
+       struct sa_entry *tmp, *next;
+
+       if (entry && entry->se_state == SA_ENTRY_SUCC) {
+               struct ll_sb_info *sbi = ll_i2sbi(sai->sai_inode);
+
+               sai->sai_hit++;
+               sai->sai_consecutive_miss = 0;
+               sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
+       } else {
+               sai->sai_miss++;
+               sai->sai_consecutive_miss++;
+       }
 
        if (entry)
-               do_sa_entry_fini(sai, entry);
+               sa_kill(sai, entry);
 
-       /* drop old entry, only 'scanner' process does this, no need to lock */
-       list_for_each_entry_safe(pos, next, &sai->sai_entries, se_link) {
-               if (!is_omitted_entry(sai, pos->se_index))
+       /*
+        * kill old completed entries, only scanner process does this, no need
+        * to lock
+        */
+       list_for_each_entry_safe(tmp, next, &sai->sai_entries, se_list) {
+               if (!is_omitted_entry(sai, tmp->se_index))
                        break;
-               /* keep those whose statahead RPC not finished */
-               if (pos->se_stat == SA_ENTRY_SUCC ||
-                   pos->se_stat == SA_ENTRY_INVA)
-                       do_sa_entry_fini(sai, pos);
+               sa_kill(sai, tmp);
        }
+       wake_up(&sai->sai_thread.t_ctl_waitq);
 }
 
 /*
- * Inside lli_sa_lock.
+ * update state and sort add entry to sai_entries by index, return true if
+ * scanner is waiting on this entry.
  */
-static void
-__sa_entry_post_stat(struct ll_statahead_info *sai, struct ll_sa_entry *entry,
-                    enum se_stat stat)
+static bool
+__sa_make_ready(struct ll_statahead_info *sai, struct sa_entry *entry, int ret)
 {
-       struct ll_sa_entry *se;
-       struct list_head         *pos = &sai->sai_entries_stated;
-
-       LASSERT(entry->se_stat == SA_ENTRY_INIT);
+       struct list_head *pos = &sai->sai_entries;
+       __u64 index = entry->se_index;
+       struct sa_entry *se;
 
-       if (!list_empty(&entry->se_list))
-               list_del_init(&entry->se_list);
+       LASSERT(!sa_ready(entry));
+       LASSERT(list_empty(&entry->se_list));
 
-       list_for_each_entry_reverse(se, &sai->sai_entries_stated, se_list) {
+       list_for_each_entry_reverse(se, &sai->sai_entries, se_list) {
                if (se->se_index < entry->se_index) {
                        pos = &se->se_list;
                        break;
                }
        }
-
        list_add(&entry->se_list, pos);
-       entry->se_stat = stat;
+       entry->se_state = ret < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC;
+
+       return (index == sai->sai_index_wait);
 }
 
 /*
- * Move entry to sai_entries_stated and sort with the index.
- * \retval 1    -- entry to be destroyed.
- * \retval 0    -- entry is inserted into stated list.
+ * release resources used in async stat RPC, update entry state and wakeup if
+ * scanner process it waiting on this entry.
  */
 static void
-sa_entry_post_stat(struct ll_statahead_info *sai, struct ll_sa_entry *entry,
-                  enum se_stat stat)
+sa_make_ready(struct ll_statahead_info *sai, struct sa_entry *entry, int ret)
 {
        struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
        struct md_enqueue_info *minfo = entry->se_minfo;
        struct ptlrpc_request *req = entry->se_req;
+       bool wakeup;
 
        /* release resources used in RPC */
        if (minfo) {
@@ -394,12 +348,15 @@ sa_entry_post_stat(struct ll_statahead_info *sai, struct ll_sa_entry *entry,
        }
 
        spin_lock(&lli->lli_sa_lock);
-       __sa_entry_post_stat(sai, entry, stat);
+       wakeup = __sa_make_ready(sai, entry, ret);
        spin_unlock(&lli->lli_sa_lock);
+
+       if (wakeup)
+               wake_up(&sai->sai_waitq);
 }
 
 /*
- * Insert inode into the list of sai_entries_agl.
+ * Insert inode into the list of sai_agls.
  */
 static void ll_agl_add(struct ll_statahead_info *sai,
                       struct inode *inode, int index)
@@ -417,9 +374,9 @@ static void ll_agl_add(struct ll_statahead_info *sai,
 
                igrab(inode);
                spin_lock(&parent->lli_agl_lock);
-               if (list_empty(&sai->sai_entries_agl))
+               if (list_empty(&sai->sai_agls))
                        added = 1;
-               list_add_tail(&child->lli_agl_list, &sai->sai_entries_agl);
+               list_add_tail(&child->lli_agl_list, &sai->sai_agls);
                spin_unlock(&parent->lli_agl_lock);
        } else {
                spin_unlock(&child->lli_agl_lock);
@@ -429,6 +386,7 @@ static void ll_agl_add(struct ll_statahead_info *sai,
                wake_up(&sai->sai_agl_thread.t_ctl_waitq);
 }
 
+/* allocate sai */
 static struct ll_statahead_info *ll_sai_alloc(void)
 {
        struct ll_statahead_info *sai;
@@ -452,10 +410,9 @@ static struct ll_statahead_info *ll_sai_alloc(void)
        init_waitqueue_head(&sai->sai_thread.t_ctl_waitq);
        init_waitqueue_head(&sai->sai_agl_thread.t_ctl_waitq);
 
+       INIT_LIST_HEAD(&sai->sai_interim_entries);
        INIT_LIST_HEAD(&sai->sai_entries);
-       INIT_LIST_HEAD(&sai->sai_entries_received);
-       INIT_LIST_HEAD(&sai->sai_entries_stated);
-       INIT_LIST_HEAD(&sai->sai_entries_agl);
+       INIT_LIST_HEAD(&sai->sai_agls);
 
        for (i = 0; i < LL_SA_CACHE_SIZE; i++) {
                INIT_LIST_HEAD(&sai->sai_cache[i]);
@@ -486,7 +443,7 @@ static void ll_sai_put(struct ll_statahead_info *sai)
 
        if (atomic_dec_and_lock(&sai->sai_refcount, &lli->lli_sa_lock)) {
                struct ll_sb_info *sbi = ll_i2sbi(sai->sai_inode);
-               struct ll_sa_entry *entry, *next;
+               struct sa_entry *entry, *next;
 
                lli->lli_sai = NULL;
                spin_unlock(&lli->lli_sa_lock);
@@ -494,14 +451,14 @@ static void ll_sai_put(struct ll_statahead_info *sai)
                LASSERT(thread_is_stopped(&sai->sai_thread));
                LASSERT(thread_is_stopped(&sai->sai_agl_thread));
                LASSERT(sai->sai_sent == sai->sai_replied);
+               LASSERT(!sa_has_callback(sai));
 
                list_for_each_entry_safe(entry, next, &sai->sai_entries,
-                                        se_link)
-                       do_sa_entry_fini(sai, entry);
+                                        se_list)
+                       sa_kill(sai, entry);
 
                LASSERT(atomic_read(&sai->sai_cache_count) == 0);
-               LASSERT(list_empty(&sai->sai_entries_agl));
-               LASSERT(atomic_read(&sai->sai_refcount) == 0);
+               LASSERT(list_empty(&sai->sai_agls));
 
                iput(sai->sai_inode);
                kfree(sai);
@@ -509,7 +466,7 @@ static void ll_sai_put(struct ll_statahead_info *sai)
        }
 }
 
-/* Do NOT forget to drop inode refcount when into sai_entries_agl. */
+/* Do NOT forget to drop inode refcount when into sai_agls. */
 static void ll_agl_trigger(struct inode *inode, struct ll_statahead_info *sai)
 {
        struct ll_inode_info *lli   = ll_i2info(inode);
@@ -569,9 +526,12 @@ static void ll_agl_trigger(struct inode *inode, struct ll_statahead_info *sai)
        iput(inode);
 }
 
-/* prepare inode for received statahead entry, and add it into agl list */
-static void sa_post_one(struct ll_statahead_info *sai,
-                       struct ll_sa_entry *entry)
+/*
+ * prepare inode for sa entry, add it into agl list, now sa_entry is ready
+ * to be used by scanner process.
+ */
+static void sa_instantiate(struct ll_statahead_info *sai,
+                          struct sa_entry *entry)
 {
        struct inode       *dir   = sai->sai_inode;
        struct inode       *child;
@@ -629,8 +589,9 @@ static void sa_post_one(struct ll_statahead_info *sai,
        if (rc)
                goto out;
 
-       CDEBUG(D_DLMTRACE, "%s: setting l_data to inode "DFID"%p\n",
+       CDEBUG(D_READA, "%s: setting %.*s" DFID " l_data to inode %p\n",
               ll_get_fsname(child->i_sb, NULL, 0),
+              entry->se_qstr.len, entry->se_qstr.name,
               PFID(ll_inode2fid(child)), child);
        ll_set_lock_data(ll_i2sbi(dir)->ll_md_exp, child, it, NULL);
 
@@ -640,45 +601,42 @@ static void sa_post_one(struct ll_statahead_info *sai,
                ll_agl_add(sai, child, entry->se_index);
 
 out:
-       /* The "sa_entry_post_stat()" will drop related ldlm ibits lock
-        * reference count by calling "ll_intent_drop_lock()" in spite of the
-        * above operations failed or not. Do not worry about calling
-        * "ll_intent_drop_lock()" more than once.
+       /*
+        * sa_make_ready() will drop ldlm ibits lock refcount by calling
+        * ll_intent_drop_lock() in spite of failures. Do not worry about
+        * calling ll_intent_drop_lock() more than once.
         */
-       sa_entry_post_stat(sai, entry, rc < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC);
-       if (entry->se_index == sai->sai_index_wait)
-               wake_up(&sai->sai_waitq);
-       ll_sa_entry_put(sai, entry);
+       sa_make_ready(sai, entry, rc);
 }
 
-static void ll_post_statahead(struct ll_statahead_info *sai)
+/* once there are async stat replies, instantiate sa_entry */
+static void sa_handle_callback(struct ll_statahead_info *sai)
 {
        struct ll_inode_info *lli;
 
        lli = ll_i2info(sai->sai_inode);
 
-       while (!sa_received_empty(sai)) {
-               struct ll_sa_entry *entry;
+       while (sa_has_callback(sai)) {
+               struct sa_entry *entry;
 
                spin_lock(&lli->lli_sa_lock);
-               if (unlikely(sa_received_empty(sai))) {
+               if (unlikely(!sa_has_callback(sai))) {
                        spin_unlock(&lli->lli_sa_lock);
                        break;
                }
-               entry = list_entry(sai->sai_entries_received.next,
-                                  struct ll_sa_entry, se_list);
-               atomic_inc(&entry->se_refcount);
+               entry = list_entry(sai->sai_interim_entries.next,
+                                  struct sa_entry, se_list);
                list_del_init(&entry->se_list);
                spin_unlock(&lli->lli_sa_lock);
 
-               sa_post_one(sai, entry);
+               sa_instantiate(sai, entry);
        }
 
        spin_lock(&lli->lli_agl_lock);
        while (!agl_list_empty(sai)) {
                struct ll_inode_info *clli;
 
-               clli = list_entry(sai->sai_entries_agl.next,
+               clli = list_entry(sai->sai_agls.next,
                                  struct ll_inode_info, lli_agl_list);
                list_del_init(&clli->lli_agl_list);
                spin_unlock(&lli->lli_agl_lock);
@@ -690,29 +648,38 @@ static void ll_post_statahead(struct ll_statahead_info *sai)
        spin_unlock(&lli->lli_agl_lock);
 }
 
+/*
+ * callback for async stat, because this is called in ptlrpcd context, we only
+ * put sa_entry in sai_cb_entries list, and let sa_handle_callback() to really
+ * prepare inode and instantiate sa_entry later.
+ */
 static int ll_statahead_interpret(struct ptlrpc_request *req,
                                  struct md_enqueue_info *minfo, int rc)
 {
        struct lookup_intent     *it  = &minfo->mi_it;
        struct inode         *dir = minfo->mi_dir;
        struct ll_inode_info     *lli = ll_i2info(dir);
-       struct ll_statahead_info *sai = NULL;
-       struct ll_sa_entry       *entry;
-       int                    wakeup;
+       struct ll_statahead_info *sai = lli->lli_sai;
+       struct sa_entry *entry = (struct sa_entry *)minfo->mi_cbdata;
+       bool wakeup;
 
        if (it_disposition(it, DISP_LOOKUP_NEG))
                rc = -ENOENT;
 
-       sai = ll_sai_get(dir);
+       /*
+        * because statahead thread will wait for all inflight RPC to finish,
+        * sai should be always valid, no need to refcount
+        */
        LASSERT(sai);
        LASSERT(!thread_is_stopped(&sai->sai_thread));
+       LASSERT(entry);
+
+       CDEBUG(D_READA, "sa_entry %.*s rc %d\n",
+              entry->se_qstr.len, entry->se_qstr.name, rc);
 
        spin_lock(&lli->lli_sa_lock);
-       entry = ll_sa_entry_get_byindex(sai, minfo->mi_cbdata);
-       LASSERT(entry);
        if (rc) {
-               __sa_entry_post_stat(sai, entry, SA_ENTRY_INVA);
-               wakeup = (entry->se_index == sai->sai_index_wait);
+               wakeup = __sa_make_ready(sai, entry, rc);
        } else {
                entry->se_minfo = minfo;
                entry->se_req = ptlrpc_request_addref(req);
@@ -724,27 +691,24 @@ static int ll_statahead_interpret(struct ptlrpc_request *req,
                 */
                entry->se_handle = it->it_lock_handle;
                ll_intent_drop_lock(it);
-               wakeup = sa_received_empty(sai);
-               list_add_tail(&entry->se_list, &sai->sai_entries_received);
+               wakeup = !sa_has_callback(sai);
+               list_add_tail(&entry->se_list, &sai->sai_interim_entries);
        }
        sai->sai_replied++;
-       spin_unlock(&lli->lli_sa_lock);
 
-       ll_sa_entry_put(sai, entry);
        if (wakeup)
                wake_up(&sai->sai_thread.t_ctl_waitq);
+       spin_unlock(&lli->lli_sa_lock);
 
        if (rc) {
                ll_intent_release(it);
                iput(dir);
                kfree(minfo);
        }
-       if (sai)
-               ll_sai_put(sai);
        return rc;
 }
 
-static void sa_args_fini(struct md_enqueue_info *minfo,
+static void sa_fini_data(struct md_enqueue_info *minfo,
                         struct ldlm_enqueue_info *einfo)
 {
        LASSERT(minfo && einfo);
@@ -756,8 +720,8 @@ static void sa_args_fini(struct md_enqueue_info *minfo,
 /**
  * prepare arguments for async stat RPC.
  */
-static int sa_args_init(struct inode *dir, struct inode *child,
-                       struct ll_sa_entry *entry, struct md_enqueue_info **pmi,
+static int sa_prep_data(struct inode *dir, struct inode *child,
+                       struct sa_entry *entry, struct md_enqueue_info **pmi,
                        struct ldlm_enqueue_info **pei)
 {
        const struct qstr      *qstr = &entry->se_qstr;
@@ -786,7 +750,7 @@ static int sa_args_init(struct inode *dir, struct inode *child,
        minfo->mi_it.it_op = IT_GETATTR;
        minfo->mi_dir = igrab(dir);
        minfo->mi_cb = ll_statahead_interpret;
-       minfo->mi_cbdata = entry->se_index;
+       minfo->mi_cbdata = entry;
 
        einfo->ei_type   = LDLM_IBITS;
        einfo->ei_mode   = it_to_lock_mode(&minfo->mi_it);
@@ -801,19 +765,19 @@ static int sa_args_init(struct inode *dir, struct inode *child,
        return 0;
 }
 
-static int do_sa_lookup(struct inode *dir, struct ll_sa_entry *entry)
+static int sa_lookup(struct inode *dir, struct sa_entry *entry)
 {
        struct md_enqueue_info   *minfo;
        struct ldlm_enqueue_info *einfo;
        int                    rc;
 
-       rc = sa_args_init(dir, NULL, entry, &minfo, &einfo);
+       rc = sa_prep_data(dir, NULL, entry, &minfo, &einfo);
        if (rc)
                return rc;
 
        rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
        if (rc < 0)
-               sa_args_fini(minfo, einfo);
+               sa_fini_data(minfo, einfo);
 
        return rc;
 }
@@ -824,8 +788,8 @@ static int do_sa_lookup(struct inode *dir, struct ll_sa_entry *entry)
  * \retval      0 -- will send stat-ahead request
  * \retval others -- prepare stat-ahead request failed
  */
-static int do_sa_revalidate(struct inode *dir, struct ll_sa_entry *entry,
-                           struct dentry *dentry)
+static int sa_revalidate(struct inode *dir, struct sa_entry *entry,
+                        struct dentry *dentry)
 {
        struct inode         *inode = d_inode(dentry);
        struct lookup_intent      it = { .it_op = IT_GETATTR,
@@ -849,7 +813,7 @@ static int do_sa_revalidate(struct inode *dir, struct ll_sa_entry *entry,
                return 1;
        }
 
-       rc = sa_args_init(dir, inode, entry, &minfo, &einfo);
+       rc = sa_prep_data(dir, inode, entry, &minfo, &einfo);
        if (rc) {
                entry->se_inode = NULL;
                iput(inode);
@@ -860,32 +824,30 @@ static int do_sa_revalidate(struct inode *dir, struct ll_sa_entry *entry,
        if (rc < 0) {
                entry->se_inode = NULL;
                iput(inode);
-               sa_args_fini(minfo, einfo);
+               sa_fini_data(minfo, einfo);
        }
 
        return rc;
 }
 
-static void ll_statahead_one(struct dentry *parent, const char *name,
-                            const int name_len)
+static void sa_statahead(struct dentry *parent, const char *name, int len)
 {
        struct inode         *dir    = d_inode(parent);
        struct ll_inode_info     *lli    = ll_i2info(dir);
        struct ll_statahead_info *sai    = lli->lli_sai;
        struct dentry       *dentry = NULL;
-       struct ll_sa_entry       *entry;
+       struct sa_entry *entry;
        int                    rc;
 
-       entry = ll_sa_entry_alloc(parent, sai, sai->sai_index, name,
-                                 name_len);
+       entry = sa_alloc(parent, sai, sai->sai_index, name, len);
        if (IS_ERR(entry))
                return;
 
        dentry = d_lookup(parent, &entry->se_qstr);
        if (!dentry) {
-               rc = do_sa_lookup(dir, entry);
+               rc = sa_lookup(dir, entry);
        } else {
-               rc = do_sa_revalidate(dir, entry, dentry);
+               rc = sa_revalidate(dir, entry, dentry);
                if (rc == 1 && agl_should_run(sai, d_inode(dentry)))
                        ll_agl_add(sai, d_inode(dentry), entry->se_index);
        }
@@ -893,18 +855,12 @@ static void ll_statahead_one(struct dentry *parent, const char *name,
        if (dentry)
                dput(dentry);
 
-       if (rc) {
-               sa_entry_post_stat(sai, entry,
-                                  rc < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC);
-               if (entry->se_index == sai->sai_index_wait)
-                       wake_up(&sai->sai_waitq);
-       } else {
+       if (rc)
+               sa_make_ready(sai, entry, rc);
+       else
                sai->sai_sent++;
-       }
 
        sai->sai_index++;
-       /* drop one refcount on entry by ll_sa_entry_alloc */
-       ll_sa_entry_put(sai, entry);
 }
 
 static int ll_agl_thread(void *arg)
@@ -938,7 +894,7 @@ static int ll_agl_thread(void *arg)
 
        while (1) {
                l_wait_event(thread->t_ctl_waitq,
-                            !list_empty(&sai->sai_entries_agl) ||
+                            !list_empty(&sai->sai_agls) ||
                             !thread_is_running(thread),
                             &lwi);
 
@@ -949,8 +905,8 @@ static int ll_agl_thread(void *arg)
                /* The statahead thread maybe help to process AGL entries,
                 * so check whether list empty again.
                 */
-               if (!list_empty(&sai->sai_entries_agl)) {
-                       clli = list_entry(sai->sai_entries_agl.next,
+               if (!list_empty(&sai->sai_agls)) {
+                       clli = list_entry(sai->sai_agls.next,
                                          struct ll_inode_info, lli_agl_list);
                        list_del_init(&clli->lli_agl_list);
                        spin_unlock(&plli->lli_agl_lock);
@@ -962,8 +918,8 @@ static int ll_agl_thread(void *arg)
 
        spin_lock(&plli->lli_agl_lock);
        sai->sai_agl_valid = 0;
-       while (!list_empty(&sai->sai_entries_agl)) {
-               clli = list_entry(sai->sai_entries_agl.next,
+       while (!list_empty(&sai->sai_agls)) {
+               clli = list_entry(sai->sai_agls.next,
                                  struct ll_inode_info, lli_agl_list);
                list_del_init(&clli->lli_agl_list);
                spin_unlock(&plli->lli_agl_lock);
@@ -1118,15 +1074,15 @@ static int ll_statahead_thread(void *arg)
                        do {
                                l_wait_event(thread->t_ctl_waitq,
                                             !sa_sent_full(sai) ||
-                                            !list_empty(&sai->sai_entries_received) ||
-                                            !list_empty(&sai->sai_entries_agl) ||
+                                            sa_has_callback(sai) ||
+                                            !list_empty(&sai->sai_agls) ||
                                             !thread_is_running(thread),
                                             &lwi);
-                               ll_post_statahead(sai);
+                               sa_handle_callback(sai);
                        } while (sa_sent_full(sai) &&
                                 thread_is_running(thread));
 
-                       ll_statahead_one(parent, name, namelen);
+                       sa_statahead(parent, name, namelen);
                }
 
                pos = le64_to_cpu(dp->ldp_hash_end);
@@ -1158,12 +1114,12 @@ static int ll_statahead_thread(void *arg)
         */
        while (thread_is_running(thread)) {
                l_wait_event(thread->t_ctl_waitq,
-                            !sa_received_empty(sai) ||
+                            sa_has_callback(sai) ||
                             !agl_list_empty(sai) ||
                             !thread_is_running(thread),
                             &lwi);
 
-               ll_post_statahead(sai);
+               sa_handle_callback(sai);
        }
 out:
        if (sai->sai_agl_valid) {
@@ -1193,8 +1149,8 @@ out:
                             sai->sai_sent == sai->sai_replied, &lwi);
        }
 
-       /* release resources held by received entries. */
-       ll_post_statahead(sai);
+       /* release resources held by statahead RPCs */
+       sa_handle_callback(sai);
 
        spin_lock(&lli->lli_sa_lock);
        thread_set_flags(thread, SVC_STOPPED);
@@ -1251,7 +1207,7 @@ void ll_deauthorize_statahead(struct inode *dir, void *key)
        if (sai && thread_is_running(&sai->sai_thread)) {
                /*
                 * statahead thread may not quit yet because it needs to cache
-                * stated entries, now it's time to tell it to quit.
+                * entries, now it's time to tell it to quit.
                 */
                thread_set_flags(&sai->sai_thread, SVC_STOPPING);
                wake_up(&sai->sai_thread.t_ctl_waitq);
@@ -1389,29 +1345,12 @@ out:
        return rc;
 }
 
-static void
-ll_sai_unplug(struct ll_statahead_info *sai, struct ll_sa_entry *entry)
-{
-       if (entry && entry->se_stat == SA_ENTRY_SUCC) {
-               struct ll_sb_info *sbi = ll_i2sbi(sai->sai_inode);
-
-               sai->sai_hit++;
-               sai->sai_consecutive_miss = 0;
-               sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
-       } else {
-               sai->sai_miss++;
-               sai->sai_consecutive_miss++;
-       }
-       ll_sa_entry_fini(sai, entry);
-       wake_up(&sai->sai_thread.t_ctl_waitq);
-}
-
 static int revalidate_statahead_dentry(struct inode *dir,
                                       struct ll_statahead_info *sai,
                                       struct dentry **dentryp,
                                       int only_unplug)
 {
-       struct ll_sa_entry *entry = NULL;
+       struct sa_entry *entry = NULL;
        struct l_wait_info lwi = { 0 };
        int rc = 0;
 
@@ -1442,31 +1381,31 @@ static int revalidate_statahead_dentry(struct inode *dir,
                }
        }
 
-       entry = ll_sa_entry_get_byname(sai, &(*dentryp)->d_name);
+       entry = sa_get(sai, &(*dentryp)->d_name);
        if (!entry || only_unplug) {
-               ll_sai_unplug(sai, entry);
+               sa_put(sai, entry);
                return entry ? 1 : -EAGAIN;
        }
 
        /* if statahead is busy in readdir, help it do post-work */
-       if (!ll_sa_entry_stated(entry) && sai->sai_in_readpage)
-               ll_post_statahead(sai);
+       if (!sa_ready(entry) && sai->sai_in_readpage)
+               sa_handle_callback(sai);
 
-       if (!ll_sa_entry_stated(entry)) {
+       if (!sa_ready(entry)) {
                sai->sai_index_wait = entry->se_index;
                lwi = LWI_TIMEOUT_INTR(cfs_time_seconds(30), NULL,
                                       LWI_ON_SIGNAL_NOOP, NULL);
                rc = l_wait_event(sai->sai_waitq,
-                                 ll_sa_entry_stated(entry) ||
+                                 sa_ready(entry) ||
                                  thread_is_stopped(&sai->sai_thread),
                                  &lwi);
                if (rc < 0) {
-                       ll_sai_unplug(sai, entry);
+                       sa_put(sai, entry);
                        return -EAGAIN;
                }
        }
 
-       if (entry->se_stat == SA_ENTRY_SUCC && entry->se_inode) {
+       if (entry->se_state == SA_ENTRY_SUCC && entry->se_inode) {
                struct inode *inode = entry->se_inode;
                struct lookup_intent it = { .it_op = IT_GETATTR,
                                            .it_lock_handle = entry->se_handle };
@@ -1480,7 +1419,7 @@ static int revalidate_statahead_dentry(struct inode *dir,
 
                                alias = ll_splice_alias(inode, *dentryp);
                                if (IS_ERR(alias)) {
-                                       ll_sai_unplug(sai, entry);
+                                       sa_put(sai, entry);
                                        return PTR_ERR(alias);
                                }
                                *dentryp = alias;
@@ -1507,7 +1446,7 @@ static int revalidate_statahead_dentry(struct inode *dir,
                }
        }
 out_unplug:
-       ll_sai_unplug(sai, entry);
+       sa_put(sai, entry);
        return rc;
 }