Whamcloud - gitweb
LU-13134 obdclass: use offset instead of cp_linkage 28/37428/12
authorWang Shilong <wshilong@ddn.com>
Tue, 4 Feb 2020 13:44:23 +0000 (21:44 +0800)
committerOleg Drokin <green@whamcloud.com>
Sat, 4 Jul 2020 03:03:03 +0000 (03:03 +0000)
Since we have fixed-size cl_page allocations, we could use
offset array to store every slices pointer for cl_page.

With this patch, we will reduce cl_page size from 392 bytes
to 336 bytes which means we could allocate from 10 to 12 objects.

Change-Id: I323bd589941125bfddf104f53a335d0cfee5c548
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/37428
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
lustre/include/cl_object.h
lustre/obdclass/cl_page.c

index abd341d..668158b 100644 (file)
@@ -737,8 +737,10 @@ struct cl_page {
        struct page             *cp_vmpage;
        /** Linkage of pages within group. Pages must be owned */
        struct list_head         cp_batch;
-       /** List of slices. Immutable after creation. */
-       struct list_head         cp_layers;
+       /** array of slices offset. Immutable after creation. */
+       unsigned char            cp_layer_offset[3];
+       /** current slice index */
+       unsigned char            cp_layer_count:2;
        /**
         * Page state. This field is const to avoid accidental update, it is
         * modified only internally within cl_page.c. Protected by a VM lock.
@@ -781,8 +783,6 @@ struct cl_page_slice {
          */
         struct cl_object                *cpl_obj;
         const struct cl_page_operations *cpl_ops;
-        /** Linkage into cl_page::cp_layers. Immutable after creation. */
-       struct list_head                 cpl_linkage;
 };
 
 /**
index 61c63a4..c86b97d 100644 (file)
@@ -123,23 +123,49 @@ static void cl_page_get_trust(struct cl_page *page)
        atomic_inc(&page->cp_ref);
 }
 
+static struct cl_page_slice *
+cl_page_slice_get(const struct cl_page *cl_page, int index)
+{
+       if (index < 0 || index >= cl_page->cp_layer_count)
+               return NULL;
+
+       /* To get the cp_layer_offset values fit under 256 bytes, we
+        * use the offset beyond the end of struct cl_page.
+        */
+       return (struct cl_page_slice *)((char *)cl_page + sizeof(*cl_page) +
+                                       cl_page->cp_layer_offset[index]);
+}
+
+#define cl_page_slice_for_each(cl_page, slice, i)              \
+       for (i = 0, slice = cl_page_slice_get(cl_page, 0);      \
+            i < (cl_page)->cp_layer_count;                     \
+            slice = cl_page_slice_get(cl_page, ++i))
+
+#define cl_page_slice_for_each_reverse(cl_page, slice, i)      \
+       for (i = (cl_page)->cp_layer_count - 1,                 \
+            slice = cl_page_slice_get(cl_page, i); i >= 0;     \
+            slice = cl_page_slice_get(cl_page, --i))
+
 /**
- * Returns a slice within a page, corresponding to the given layer in the
+ * Returns a slice within a cl_page, corresponding to the given layer in the
  * device stack.
  *
  * \see cl_lock_at()
  */
 static const struct cl_page_slice *
-cl_page_at_trusted(const struct cl_page *page,
+cl_page_at_trusted(const struct cl_page *cl_page,
                    const struct lu_device_type *dtype)
 {
        const struct cl_page_slice *slice;
+       int i;
+
        ENTRY;
 
-       list_for_each_entry(slice, &page->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_obj->co_lu.lo_dev->ld_type == dtype)
                        RETURN(slice);
        }
+
        RETURN(NULL);
 }
 
@@ -156,32 +182,31 @@ static void __cl_page_free(struct cl_page *cl_page, unsigned short bufsize)
        }
 }
 
-static void cl_page_free(const struct lu_env *env, struct cl_page *page,
+static void cl_page_free(const struct lu_env *env, struct cl_page *cl_page,
                         struct pagevec *pvec)
 {
-       struct cl_object *obj  = page->cp_obj;
+       struct cl_object *obj  = cl_page->cp_obj;
        unsigned short bufsize = cl_object_header(obj)->coh_page_bufsize;
-
-       PASSERT(env, page, list_empty(&page->cp_batch));
-       PASSERT(env, page, page->cp_owner == NULL);
-       PASSERT(env, page, page->cp_state == CPS_FREEING);
+       struct cl_page_slice *slice;
+       int i;
 
        ENTRY;
-       while (!list_empty(&page->cp_layers)) {
-               struct cl_page_slice *slice;
+       PASSERT(env, cl_page, list_empty(&cl_page->cp_batch));
+       PASSERT(env, cl_page, cl_page->cp_owner == NULL);
+       PASSERT(env, cl_page, cl_page->cp_state == CPS_FREEING);
 
-               slice = list_entry(page->cp_layers.next,
-                                  struct cl_page_slice, cpl_linkage);
-               list_del_init(page->cp_layers.next);
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (unlikely(slice->cpl_ops->cpo_fini != NULL))
                        slice->cpl_ops->cpo_fini(env, slice, pvec);
        }
+       cl_page->cp_layer_count = 0;
        cs_page_dec(obj, CS_total);
-       cs_pagestate_dec(obj, page->cp_state);
-       lu_object_ref_del_at(&obj->co_lu, &page->cp_obj_ref, "cl_page", page);
+       cs_pagestate_dec(obj, cl_page->cp_state);
+       lu_object_ref_del_at(&obj->co_lu, &cl_page->cp_obj_ref,
+                            "cl_page", cl_page);
        cl_object_put(env, obj);
-       lu_ref_fini(&page->cp_reference);
-       __cl_page_free(page, bufsize);
+       lu_ref_fini(&cl_page->cp_reference);
+       __cl_page_free(cl_page, bufsize);
        EXIT;
 }
 
@@ -269,7 +294,6 @@ struct cl_page *cl_page_alloc(const struct lu_env *env,
                page->cp_vmpage = vmpage;
                cl_page_state_set_trust(page, CPS_CACHED);
                page->cp_type = type;
-               INIT_LIST_HEAD(&page->cp_layers);
                INIT_LIST_HEAD(&page->cp_batch);
                lu_ref_init(&page->cp_reference);
                head = o->co_lu.lo_header;
@@ -537,30 +561,33 @@ static void cl_page_owner_set(struct cl_page *page)
 }
 
 void cl_page_disown0(const struct lu_env *env,
-                     struct cl_io *io, struct cl_page *pg)
+                    struct cl_io *io, struct cl_page *cl_page)
 {
        const struct cl_page_slice *slice;
-        enum cl_page_state state;
+       enum cl_page_state state;
+       int i;
 
         ENTRY;
-        state = pg->cp_state;
-        PINVRNT(env, pg, state == CPS_OWNED || state == CPS_FREEING);
-        PINVRNT(env, pg, cl_page_invariant(pg) || state == CPS_FREEING);
-        cl_page_owner_clear(pg);
-
-        if (state == CPS_OWNED)
-                cl_page_state_set(env, pg, CPS_CACHED);
+       state = cl_page->cp_state;
+       PINVRNT(env, cl_page, state == CPS_OWNED ||
+               state == CPS_FREEING);
+       PINVRNT(env, cl_page, cl_page_invariant(cl_page) ||
+               state == CPS_FREEING);
+       cl_page_owner_clear(cl_page);
+
+       if (state == CPS_OWNED)
+               cl_page_state_set(env, cl_page, CPS_CACHED);
         /*
-         * Completion call-backs are executed in the bottom-up order, so that
-         * uppermost layer (llite), responsible for VFS/VM interaction runs
-         * last and can release locks safely.
-         */
-       list_for_each_entry_reverse(slice, &pg->cp_layers, cpl_linkage) {
+        * Completion call-backs are executed in the bottom-up order, so that
+        * uppermost layer (llite), responsible for VFS/VM interaction runs
+        * last and can release locks safely.
+        */
+       cl_page_slice_for_each_reverse(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_disown != NULL)
                        (*slice->cpl_ops->cpo_disown)(env, slice, io);
        }
 
-        EXIT;
+       EXIT;
 }
 
 /**
@@ -581,12 +608,12 @@ EXPORT_SYMBOL(cl_page_is_owned);
  * Waits until page is in cl_page_state::CPS_CACHED state, and then switch it
  * into cl_page_state::CPS_OWNED state.
  *
- * \pre  !cl_page_is_owned(pg, io)
- * \post result == 0 iff cl_page_is_owned(pg, io)
+ * \pre  !cl_page_is_owned(cl_page, io)
+ * \post result == 0 iff cl_page_is_owned(cl_page, io)
  *
  * \retval 0   success
  *
- * \retval -ve failure, e.g., page was destroyed (and landed in
+ * \retval -ve failure, e.g., cl_page was destroyed (and landed in
  *             cl_page_state::CPS_FREEING instead of cl_page_state::CPS_CACHED).
  *             or, page was owned by another thread, or in IO.
  *
@@ -596,48 +623,47 @@ EXPORT_SYMBOL(cl_page_is_owned);
  * \see cl_page_own
  */
 static int cl_page_own0(const struct lu_env *env, struct cl_io *io,
-                        struct cl_page *pg, int nonblock)
+                       struct cl_page *cl_page, int nonblock)
 {
-       int result = 0;
        const struct cl_page_slice *slice;
+       int result = 0;
+       int i;
 
-        PINVRNT(env, pg, !cl_page_is_owned(pg, io));
-
-        ENTRY;
+       ENTRY;
+       PINVRNT(env, cl_page, !cl_page_is_owned(cl_page, io));
         io = cl_io_top(io);
 
-        if (pg->cp_state == CPS_FREEING) {
-                result = -ENOENT;
+       if (cl_page->cp_state == CPS_FREEING) {
+               result = -ENOENT;
                goto out;
        }
 
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_own)
                        result = (*slice->cpl_ops->cpo_own)(env, slice,
                                                            io, nonblock);
-
                if (result != 0)
                        break;
-
        }
        if (result > 0)
                result = 0;
 
        if (result == 0) {
-               PASSERT(env, pg, pg->cp_owner == NULL);
-               pg->cp_owner = cl_io_top(io);
-               cl_page_owner_set(pg);
-               if (pg->cp_state != CPS_FREEING) {
-                       cl_page_state_set(env, pg, CPS_OWNED);
+               PASSERT(env, cl_page, cl_page->cp_owner == NULL);
+               cl_page->cp_owner = cl_io_top(io);
+               cl_page_owner_set(cl_page);
+               if (cl_page->cp_state != CPS_FREEING) {
+                       cl_page_state_set(env, cl_page, CPS_OWNED);
                } else {
-                       cl_page_disown0(env, io, pg);
+                       cl_page_disown0(env, io, cl_page);
                        result = -ENOENT;
                }
        }
 
 out:
-        PINVRNT(env, pg, ergo(result == 0, cl_page_invariant(pg)));
-        RETURN(result);
+       PINVRNT(env, cl_page, ergo(result == 0,
+               cl_page_invariant(cl_page)));
+       RETURN(result);
 }
 
 /**
@@ -669,30 +695,32 @@ EXPORT_SYMBOL(cl_page_own_try);
  *
  * Called when page is already locked by the hosting VM.
  *
- * \pre !cl_page_is_owned(pg, io)
- * \post cl_page_is_owned(pg, io)
+ * \pre !cl_page_is_owned(cl_page, io)
+ * \post cl_page_is_owned(cl_page, io)
  *
  * \see cl_page_operations::cpo_assume()
  */
 void cl_page_assume(const struct lu_env *env,
-                    struct cl_io *io, struct cl_page *pg)
+                   struct cl_io *io, struct cl_page *cl_page)
 {
        const struct cl_page_slice *slice;
-
-       PINVRNT(env, pg, cl_object_same(pg->cp_obj, io->ci_obj));
+       int i;
 
        ENTRY;
+
+       PINVRNT(env, cl_page,
+               cl_object_same(cl_page->cp_obj, io->ci_obj));
        io = cl_io_top(io);
 
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_assume != NULL)
                        (*slice->cpl_ops->cpo_assume)(env, slice, io);
        }
 
-       PASSERT(env, pg, pg->cp_owner == NULL);
-       pg->cp_owner = cl_io_top(io);
-       cl_page_owner_set(pg);
-       cl_page_state_set(env, pg, CPS_OWNED);
+       PASSERT(env, cl_page, cl_page->cp_owner == NULL);
+       cl_page->cp_owner = cl_io_top(io);
+       cl_page_owner_set(cl_page);
+       cl_page_state_set(env, cl_page, CPS_OWNED);
        EXIT;
 }
 EXPORT_SYMBOL(cl_page_assume);
@@ -700,33 +728,34 @@ EXPORT_SYMBOL(cl_page_assume);
 /**
  * Releases page ownership without unlocking the page.
  *
- * Moves page into cl_page_state::CPS_CACHED without releasing a lock on the
- * underlying VM page (as VM is supposed to do this itself).
+ * Moves cl_page into cl_page_state::CPS_CACHED without releasing a lock
+ * on the underlying VM page (as VM is supposed to do this itself).
  *
- * \pre   cl_page_is_owned(pg, io)
- * \post !cl_page_is_owned(pg, io)
+ * \pre   cl_page_is_owned(cl_page, io)
+ * \post !cl_page_is_owned(cl_page, io)
  *
  * \see cl_page_assume()
  */
 void cl_page_unassume(const struct lu_env *env,
-                      struct cl_io *io, struct cl_page *pg)
+                     struct cl_io *io, struct cl_page *cl_page)
 {
        const struct cl_page_slice *slice;
-
-        PINVRNT(env, pg, cl_page_is_owned(pg, io));
-        PINVRNT(env, pg, cl_page_invariant(pg));
+       int i;
 
         ENTRY;
-        io = cl_io_top(io);
-        cl_page_owner_clear(pg);
-        cl_page_state_set(env, pg, CPS_CACHED);
+       PINVRNT(env, cl_page, cl_page_is_owned(cl_page, io));
+       PINVRNT(env, cl_page, cl_page_invariant(cl_page));
+
+       io = cl_io_top(io);
+       cl_page_owner_clear(cl_page);
+       cl_page_state_set(env, cl_page, CPS_CACHED);
 
-       list_for_each_entry_reverse(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each_reverse(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_unassume != NULL)
                        (*slice->cpl_ops->cpo_unassume)(env, slice, io);
        }
 
-        EXIT;
+       EXIT;
 }
 EXPORT_SYMBOL(cl_page_unassume);
 
@@ -755,24 +784,25 @@ void cl_page_disown(const struct lu_env *env,
 EXPORT_SYMBOL(cl_page_disown);
 
 /**
- * Called when page is to be removed from the object, e.g., as a result of
- * truncate.
+ * Called when cl_page is to be removed from the object, e.g.,
+ * as a result of truncate.
  *
  * Calls cl_page_operations::cpo_discard() top-to-bottom.
  *
- * \pre cl_page_is_owned(pg, io)
+ * \pre cl_page_is_owned(cl_page, io)
  *
  * \see cl_page_operations::cpo_discard()
  */
 void cl_page_discard(const struct lu_env *env,
-                     struct cl_io *io, struct cl_page *pg)
+                    struct cl_io *io, struct cl_page *cl_page)
 {
        const struct cl_page_slice *slice;
+       int i;
 
-       PINVRNT(env, pg, cl_page_is_owned(pg, io));
-       PINVRNT(env, pg, cl_page_invariant(pg));
+       PINVRNT(env, cl_page, cl_page_is_owned(cl_page, io));
+       PINVRNT(env, cl_page, cl_page_invariant(cl_page));
 
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_discard != NULL)
                        (*slice->cpl_ops->cpo_discard)(env, slice, io);
        }
@@ -781,29 +811,31 @@ EXPORT_SYMBOL(cl_page_discard);
 
 /**
  * Version of cl_page_delete() that can be called for not fully constructed
- * pages, e.g. in an error handling cl_page_find()->cl_page_delete0()
- * path. Doesn't check page invariant.
+ * cl_pages, e.g. in an error handling cl_page_find()->cl_page_delete0()
+ * path. Doesn't check cl_page invariant.
  */
-static void cl_page_delete0(const struct lu_env *env, struct cl_page *pg)
+static void cl_page_delete0(const struct lu_env *env,
+                           struct cl_page *cl_page)
 {
        const struct cl_page_slice *slice;
+       int i;
 
         ENTRY;
 
-        PASSERT(env, pg, pg->cp_state != CPS_FREEING);
+       PASSERT(env, cl_page, cl_page->cp_state != CPS_FREEING);
 
-        /*
-         * Severe all ways to obtain new pointers to @pg.
-         */
-        cl_page_owner_clear(pg);
-        cl_page_state_set0(env, pg, CPS_FREEING);
+       /*
+        * Severe all ways to obtain new pointers to @pg.
+        */
+       cl_page_owner_clear(cl_page);
+       cl_page_state_set0(env, cl_page, CPS_FREEING);
 
-       list_for_each_entry_reverse(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each_reverse(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_delete != NULL)
                        (*slice->cpl_ops->cpo_delete)(env, slice);
        }
 
-        EXIT;
+       EXIT;
 }
 
 /**
@@ -848,13 +880,15 @@ EXPORT_SYMBOL(cl_page_delete);
  *
  * \see cl_page_operations::cpo_export()
  */
-void cl_page_export(const struct lu_env *env, struct cl_page *pg, int uptodate)
+void cl_page_export(const struct lu_env *env, struct cl_page *cl_page,
+                   int uptodate)
 {
        const struct cl_page_slice *slice;
+       int i;
 
-        PINVRNT(env, pg, cl_page_invariant(pg));
+       PINVRNT(env, cl_page, cl_page_invariant(cl_page));
 
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_export != NULL)
                        (*slice->cpl_ops->cpo_export)(env, slice, uptodate);
        }
@@ -862,37 +896,39 @@ void cl_page_export(const struct lu_env *env, struct cl_page *pg, int uptodate)
 EXPORT_SYMBOL(cl_page_export);
 
 /**
- * Returns true, iff \a pg is VM locked in a suitable sense by the calling
+ * Returns true, if \a page is VM locked in a suitable sense by the calling
  * thread.
  */
-int cl_page_is_vmlocked(const struct lu_env *env, const struct cl_page *pg)
+int cl_page_is_vmlocked(const struct lu_env *env,
+                       const struct cl_page *cl_page)
 {
         const struct cl_page_slice *slice;
        int result;
 
-        ENTRY;
-        slice = container_of(pg->cp_layers.next,
-                             const struct cl_page_slice, cpl_linkage);
-        PASSERT(env, pg, slice->cpl_ops->cpo_is_vmlocked != NULL);
+       ENTRY;
+       slice = cl_page_slice_get(cl_page, 0);
+       PASSERT(env, cl_page, slice->cpl_ops->cpo_is_vmlocked != NULL);
         /*
-         * Call ->cpo_is_vmlocked() directly instead of going through
+        * Call ->cpo_is_vmlocked() directly instead of going through
          * CL_PAGE_INVOKE(), because cl_page_is_vmlocked() is used by
          * cl_page_invariant().
          */
         result = slice->cpl_ops->cpo_is_vmlocked(env, slice);
-        PASSERT(env, pg, result == -EBUSY || result == -ENODATA);
-        RETURN(result == -EBUSY);
+       PASSERT(env, cl_page, result == -EBUSY || result == -ENODATA);
+
+       RETURN(result == -EBUSY);
 }
 EXPORT_SYMBOL(cl_page_is_vmlocked);
 
-void cl_page_touch(const struct lu_env *env, const struct cl_page *pg,
-                 size_t to)
+void cl_page_touch(const struct lu_env *env,
+                  const struct cl_page *cl_page, size_t to)
 {
        const struct cl_page_slice *slice;
+       int i;
 
        ENTRY;
 
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_page_touch != NULL)
                        (*slice->cpl_ops->cpo_page_touch)(env, slice, to);
        }
@@ -927,40 +963,39 @@ static void cl_page_io_start(const struct lu_env *env,
  * transfer now.
  */
 int cl_page_prep(const struct lu_env *env, struct cl_io *io,
-                 struct cl_page *pg, enum cl_req_type crt)
+                struct cl_page *cl_page, enum cl_req_type crt)
 {
        const struct cl_page_slice *slice;
        int result = 0;
+       int i;
 
-        PINVRNT(env, pg, cl_page_is_owned(pg, io));
-        PINVRNT(env, pg, cl_page_invariant(pg));
-        PINVRNT(env, pg, crt < CRT_NR);
+       PINVRNT(env, cl_page, cl_page_is_owned(cl_page, io));
+       PINVRNT(env, cl_page, cl_page_invariant(cl_page));
+       PINVRNT(env, cl_page, crt < CRT_NR);
 
         /*
-         * XXX this has to be called bottom-to-top, so that llite can set up
-         * PG_writeback without risking other layers deciding to skip this
-         * page.
-         */
+        * this has to be called bottom-to-top, so that llite can set up
+        * PG_writeback without risking other layers deciding to skip this
+        * page.
+        */
        if (crt >= CRT_NR)
                return -EINVAL;
 
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_own)
                        result = (*slice->cpl_ops->io[crt].cpo_prep)(env,
                                                                     slice,
                                                                     io);
-
                if (result != 0)
                        break;
-
        }
 
        if (result >= 0) {
                result = 0;
-               cl_page_io_start(env, pg, crt);
+               cl_page_io_start(env, cl_page, crt);
        }
 
-       CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", crt, result);
+       CL_PAGE_HEADER(D_TRACE, env, cl_page, "%d %d\n", crt, result);
        return result;
 }
 EXPORT_SYMBOL(cl_page_prep);
@@ -975,35 +1010,37 @@ EXPORT_SYMBOL(cl_page_prep);
  * uppermost layer (llite), responsible for the VFS/VM interaction runs last
  * and can release locks safely.
  *
- * \pre  pg->cp_state == CPS_PAGEIN || pg->cp_state == CPS_PAGEOUT
- * \post pg->cp_state == CPS_CACHED
+ * \pre  cl_page->cp_state == CPS_PAGEIN || cl_page->cp_state == CPS_PAGEOUT
+ * \post cl_page->cl_page_state == CPS_CACHED
  *
  * \see cl_page_operations::cpo_completion()
  */
 void cl_page_completion(const struct lu_env *env,
-                        struct cl_page *pg, enum cl_req_type crt, int ioret)
+                       struct cl_page *cl_page, enum cl_req_type crt,
+                       int ioret)
 {
        const struct cl_page_slice *slice;
-        struct cl_sync_io *anchor = pg->cp_sync_io;
-
-        PASSERT(env, pg, crt < CRT_NR);
-        PASSERT(env, pg, pg->cp_state == cl_req_type_state(crt));
+       struct cl_sync_io *anchor = cl_page->cp_sync_io;
+       int i;
 
         ENTRY;
-        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", crt, ioret);
-        cl_page_state_set(env, pg, CPS_CACHED);
+       PASSERT(env, cl_page, crt < CRT_NR);
+       PASSERT(env, cl_page, cl_page->cp_state == cl_req_type_state(crt));
+
+       CL_PAGE_HEADER(D_TRACE, env, cl_page, "%d %d\n", crt, ioret);
+       cl_page_state_set(env, cl_page, CPS_CACHED);
        if (crt >= CRT_NR)
                return;
 
-       list_for_each_entry_reverse(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each_reverse(cl_page, slice, i) {
                if (slice->cpl_ops->io[crt].cpo_completion != NULL)
                        (*slice->cpl_ops->io[crt].cpo_completion)(env, slice,
                                                                  ioret);
        }
 
        if (anchor != NULL) {
-               LASSERT(pg->cp_sync_io == anchor);
-               pg->cp_sync_io = NULL;
+               LASSERT(cl_page->cp_sync_io == anchor);
+               cl_page->cp_sync_io = NULL;
                cl_sync_io_note(env, anchor, ioret);
        }
        EXIT;
@@ -1014,61 +1051,61 @@ EXPORT_SYMBOL(cl_page_completion);
  * Notify layers that transfer formation engine decided to yank this page from
  * the cache and to make it a part of a transfer.
  *
- * \pre  pg->cp_state == CPS_CACHED
- * \post pg->cp_state == CPS_PAGEIN || pg->cp_state == CPS_PAGEOUT
+ * \pre  cl_page->cp_state == CPS_CACHED
+ * \post cl_page->cp_state == CPS_PAGEIN || cl_page->cp_state == CPS_PAGEOUT
  *
  * \see cl_page_operations::cpo_make_ready()
  */
-int cl_page_make_ready(const struct lu_env *env, struct cl_page *pg,
+int cl_page_make_ready(const struct lu_env *env, struct cl_page *cl_page,
                        enum cl_req_type crt)
 {
-       const struct cl_page_slice *sli;
+       const struct cl_page_slice *slice;
        int result = 0;
-
-        PINVRNT(env, pg, crt < CRT_NR);
+       int i;
 
         ENTRY;
+       PINVRNT(env, cl_page, crt < CRT_NR);
        if (crt >= CRT_NR)
                RETURN(-EINVAL);
 
-       list_for_each_entry(sli, &pg->cp_layers, cpl_linkage) {
-               if (sli->cpl_ops->io[crt].cpo_make_ready != NULL)
-                       result = (*sli->cpl_ops->io[crt].cpo_make_ready)(env,
-                                                                        sli);
+       cl_page_slice_for_each(cl_page, slice, i) {
+               if (slice->cpl_ops->io[crt].cpo_make_ready != NULL)
+                       result = (*slice->cpl_ops->io[crt].cpo_make_ready)(env, slice);
                if (result != 0)
                        break;
        }
 
        if (result >= 0) {
                result = 0;
-                PASSERT(env, pg, pg->cp_state == CPS_CACHED);
-                cl_page_io_start(env, pg, crt);
+               PASSERT(env, cl_page, cl_page->cp_state == CPS_CACHED);
+               cl_page_io_start(env, cl_page, crt);
         }
-        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", crt, result);
-        RETURN(result);
+       CL_PAGE_HEADER(D_TRACE, env, cl_page, "%d %d\n", crt, result);
+
+       RETURN(result);
 }
 EXPORT_SYMBOL(cl_page_make_ready);
 
 /**
- * Called if a pge is being written back by kernel's intention.
+ * Called if a page is being written back by kernel's intention.
  *
- * \pre  cl_page_is_owned(pg, io)
- * \post ergo(result == 0, pg->cp_state == CPS_PAGEOUT)
+ * \pre  cl_page_is_owned(cl_page, io)
+ * \post ergo(result == 0, cl_page->cp_state == CPS_PAGEOUT)
  *
  * \see cl_page_operations::cpo_flush()
  */
 int cl_page_flush(const struct lu_env *env, struct cl_io *io,
-                 struct cl_page *pg)
+                 struct cl_page *cl_page)
 {
        const struct cl_page_slice *slice;
        int result = 0;
-
-       PINVRNT(env, pg, cl_page_is_owned(pg, io));
-       PINVRNT(env, pg, cl_page_invariant(pg));
+       int i;
 
        ENTRY;
+       PINVRNT(env, cl_page, cl_page_is_owned(cl_page, io));
+       PINVRNT(env, cl_page, cl_page_invariant(cl_page));
 
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_flush != NULL)
                        result = (*slice->cpl_ops->cpo_flush)(env, slice, io);
                if (result != 0)
@@ -1077,7 +1114,7 @@ int cl_page_flush(const struct lu_env *env, struct cl_io *io,
        if (result > 0)
                result = 0;
 
-       CL_PAGE_HEADER(D_TRACE, env, pg, "%d\n", result);
+       CL_PAGE_HEADER(D_TRACE, env, cl_page, "%d\n", result);
        RETURN(result);
 }
 EXPORT_SYMBOL(cl_page_flush);
@@ -1087,15 +1124,16 @@ EXPORT_SYMBOL(cl_page_flush);
  *
  * \see cl_page_operations::cpo_clip()
  */
-void cl_page_clip(const struct lu_env *env, struct cl_page *pg,
+void cl_page_clip(const struct lu_env *env, struct cl_page *cl_page,
                   int from, int to)
 {
        const struct cl_page_slice *slice;
+       int i;
 
-        PINVRNT(env, pg, cl_page_invariant(pg));
+       PINVRNT(env, cl_page, cl_page_invariant(cl_page));
 
-        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", from, to);
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       CL_PAGE_HEADER(D_TRACE, env, cl_page, "%d %d\n", from, to);
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_clip != NULL)
                        (*slice->cpl_ops->cpo_clip)(env, slice, from, to);
        }
@@ -1117,23 +1155,24 @@ void cl_page_header_print(const struct lu_env *env, void *cookie,
 EXPORT_SYMBOL(cl_page_header_print);
 
 /**
- * Prints human readable representation of \a pg to the \a f.
+ * Prints human readable representation of \a cl_page to the \a f.
  */
 void cl_page_print(const struct lu_env *env, void *cookie,
-                   lu_printer_t printer, const struct cl_page *pg)
+                  lu_printer_t printer, const struct cl_page *cl_page)
 {
        const struct cl_page_slice *slice;
        int result = 0;
+       int i;
 
-       cl_page_header_print(env, cookie, printer, pg);
-       list_for_each_entry(slice, &pg->cp_layers, cpl_linkage) {
+       cl_page_header_print(env, cookie, printer, cl_page);
+       cl_page_slice_for_each(cl_page, slice, i) {
                if (slice->cpl_ops->cpo_print != NULL)
                        result = (*slice->cpl_ops->cpo_print)(env, slice,
                                                             cookie, printer);
                if (result != 0)
                        break;
        }
-       (*printer)(env, cookie, "end page@%p\n", pg);
+       (*printer)(env, cookie, "end page@%p\n", cl_page);
 }
 EXPORT_SYMBOL(cl_page_print);
 
@@ -1170,15 +1209,20 @@ EXPORT_SYMBOL(cl_page_size);
  *
  * \see cl_lock_slice_add(), cl_req_slice_add(), cl_io_slice_add()
  */
-void cl_page_slice_add(struct cl_page *page, struct cl_page_slice *slice,
+void cl_page_slice_add(struct cl_page *cl_page, struct cl_page_slice *slice,
                       struct cl_object *obj,
                       const struct cl_page_operations *ops)
 {
+       unsigned int offset = (char *)slice -
+                       ((char *)cl_page + sizeof(*cl_page));
+
        ENTRY;
-       list_add_tail(&slice->cpl_linkage, &page->cp_layers);
+       LASSERT(offset < (1 << sizeof(cl_page->cp_layer_offset[0]) * 8));
+       cl_page->cp_layer_offset[cl_page->cp_layer_count++] = offset;
        slice->cpl_obj  = obj;
        slice->cpl_ops  = ops;
-       slice->cpl_page = page;
+       slice->cpl_page = cl_page;
+
        EXIT;
 }
 EXPORT_SYMBOL(cl_page_slice_add);