performance/readdir-ahead: introduce directory read-ahead translator

This is a translator to improve the performance of typical,
sequential directory reads (i.e., ls). readdir-ahead begins
preloading the contents of a directory on open and serves readdir
requests from the preloaded content. readdir-ahead is currently
implemented to only handle the single threaded directory read
case.

readdir-ahead is currently disabled by default. It can be enabled
with the following command:

	gluster volume set <volname> readdir-ahead on

The following are results of a getdents test on a single brick
volume.

Test info:

- Single VM, gluster client/server.
- Volume mounted with native client using --gid-timeout=2.
- getdents on single directory with 100k 0-byte files.

Test results:

- !readdir-ahead

read 3120080 bytes from offset 0
3 MiB, 4348 ops, 0:00:07.00 (416.590 KiB/sec and 594.4737 ops/sec)

- readdir-ahead

read 3120080 bytes from offset 0
3 MiB, 4348 ops, 0:00:03.00 (820.116 KiB/sec and 1170.3043 ops/sec)

BUG: 980517
Change-Id: Ieceb9e1eb47d1d5b5af8da2bf03839537364653f
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-on: http://review.gluster.org/4519
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

9 files changed, 704 insertions, 1 deletions

diff --git a/configure.ac b/configure.ac
index 6b962042c0f..f81d82dccf1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -67,6 +67,8 @@ AC_CONFIG_FILES([Makefile
                 xlators/performance/write-behind/src/Makefile
                 xlators/performance/read-ahead/Makefile
                 xlators/performance/read-ahead/src/Makefile
+                xlators/performance/readdir-ahead/Makefile
+                xlators/performance/readdir-ahead/src/Makefile
                 xlators/performance/io-threads/Makefile
                 xlators/performance/io-threads/src/Makefile
                 xlators/performance/io-cache/Makefile
diff --git a/tests/features/readdir-ahead.t b/tests/features/readdir-ahead.t
new file mode 100755
index 00000000000..c7ee637f0b2
--- /dev/null
+++ b/tests/features/readdir-ahead.t
@@ -0,0 +1,44 @@
+#!/bin/bash
+#
+# Test basic readdir-ahead functionality. Verify that readdir-ahead can be
+# enabled, create a set of files and run some ls tests.
+#
+###
+
+. $(dirname $0)/../include.rc
+
+cleanup;
+
+TEST glusterd
+
+TEST $CLI volume create $V0 $H0:$B0/$V0
+TEST $CLI volume start $V0
+
+TEST $CLI volume set $V0 readdir-ahead on
+
+TEST glusterfs --volfile-id=$V0 --volfile-server=$H0 $M0
+
+TEST mkdir $M0/test
+for i in $(seq 0 99)
+do
+	touch $M0/test/$i
+done
+
+count=`ls -1 $M0/test | wc -l`
+TEST [ $count -eq 100 ]
+
+count=`ls -1 $M0/test | wc -l`
+TEST [ $count -eq 100 ]
+
+TEST rm -rf $M0/test/*
+
+count=`ls -1 $M0/test | wc -l`
+TEST [ $count -eq 0 ]
+
+TEST rmdir $M0/test
+
+TEST umount -l $M0;
+TEST $CLI volume stop $V0
+TEST $CLI volume delete $V0
+
+cleanup;
diff --git a/xlators/mgmt/glusterd/src/glusterd-volume-set.c b/xlators/mgmt/glusterd/src/glusterd-volume-set.c
index 738cacd5683..7ec8cf75541 100644
--- a/xlators/mgmt/glusterd/src/glusterd-volume-set.c
+++ b/xlators/mgmt/glusterd/src/glusterd-volume-set.c
@@ -845,6 +845,15 @@ struct volopt_map_entry glusterd_volopt_map[] = {
           .description = "enable/disable read-ahead translator in the volume.",
           .flags       = OPT_FLAG_CLIENT_OPT | OPT_FLAG_XLATOR_OPT
         },
+        { .key         = "performance.readdir-ahead",
+          .voltype     = "performance/readdir-ahead",
+          .option      = "!perf",
+          .value       = "off",
+          .op_version  = 3,
+          .description = "enable/disable readdir-ahead translator in the volume.",
+          .flags       = OPT_FLAG_CLIENT_OPT | OPT_FLAG_XLATOR_OPT
+        },
+
         { .key         = "performance.io-cache",
           .voltype     = "performance/io-cache",
           .option      = "!perf",
diff --git a/xlators/performance/Makefile.am b/xlators/performance/Makefile.am
index f99e11829db..a494190baac 100644
--- a/xlators/performance/Makefile.am
+++ b/xlators/performance/Makefile.am
@@ -1,3 +1,3 @@
-SUBDIRS = write-behind read-ahead io-threads io-cache symlink-cache quick-read md-cache open-behind
+SUBDIRS = write-behind read-ahead readdir-ahead io-threads io-cache symlink-cache quick-read md-cache open-behind
 
 CLEANFILES = 
diff --git a/xlators/performance/readdir-ahead/Makefile.am b/xlators/performance/readdir-ahead/Makefile.am
new file mode 100644
index 00000000000..a985f42a877
--- /dev/null
+++ b/xlators/performance/readdir-ahead/Makefile.am
@@ -0,0 +1,3 @@
+SUBDIRS = src
+
+CLEANFILES =
diff --git a/xlators/performance/readdir-ahead/src/Makefile.am b/xlators/performance/readdir-ahead/src/Makefile.am
new file mode 100644
index 00000000000..cdabd14284e
--- /dev/null
+++ b/xlators/performance/readdir-ahead/src/Makefile.am
@@ -0,0 +1,15 @@
+xlator_LTLIBRARIES = readdir-ahead.la
+xlatordir = $(libdir)/glusterfs/$(PACKAGE_VERSION)/xlator/performance
+
+readdir_ahead_la_LDFLAGS = -module -avoidversion
+
+readdir_ahead_la_SOURCES = readdir-ahead.c
+readdir_ahead_la_LIBADD = $(top_builddir)/libglusterfs/src/libglusterfs.la
+
+noinst_HEADERS = readdir-ahead.h readdir-ahead-mem-types.h
+
+AM_CPPFLAGS = $(GF_CPPFLAGS) -I$(top_srcdir)/libglusterfs/src
+
+AM_CFLAGS = -Wall $(GF_CFLAGS)
+
+CLEANFILES =
diff --git a/xlators/performance/readdir-ahead/src/readdir-ahead-mem-types.h b/xlators/performance/readdir-ahead/src/readdir-ahead-mem-types.h
new file mode 100644
index 00000000000..39e2c536975
--- /dev/null
+++ b/xlators/performance/readdir-ahead/src/readdir-ahead-mem-types.h
@@ -0,0 +1,24 @@
+/*
+  Copyright (c) 2008-2013 Red Hat, Inc. <http://www.redhat.com>
+  This file is part of GlusterFS.
+
+  This file is licensed to you under your choice of the GNU Lesser
+  General Public License, version 3 or any later version (LGPLv3 or
+  later), or the GNU General Public License, version 2 (GPLv2), in all
+  cases as published by the Free Software Foundation.
+*/
+
+
+#ifndef __RDA_MEM_TYPES_H__
+#define __RDA_MEM_TYPES_H__
+
+#include "mem-types.h"
+
+enum gf_rda_mem_types_ {
+        gf_rda_mt_rda_local   = gf_common_mt_end + 1,
+	gf_rda_mt_rda_fd_ctx,
+	gf_rda_mt_rda_priv,
+        gf_rda_mt_end
+};
+
+#endif
diff --git a/xlators/performance/readdir-ahead/src/readdir-ahead.c b/xlators/performance/readdir-ahead/src/readdir-ahead.c
new file mode 100644
index 00000000000..53e6756f072
--- /dev/null
+++ b/xlators/performance/readdir-ahead/src/readdir-ahead.c
@@ -0,0 +1,560 @@
+/*
+  Copyright (c) 2008-2013 Red Hat, Inc. <http://www.redhat.com>
+  This file is part of GlusterFS.
+
+  This file is licensed to you under your choice of the GNU Lesser
+  General Public License, version 3 or any later version (LGPLv3 or
+  later), or the GNU General Public License, version 2 (GPLv2), in all
+  cases as published by the Free Software Foundation.
+*/
+
+/*
+ * performance/readdir-ahead preloads a local buffer with directory entries
+ * on opendir. The optimization involves using maximum sized gluster rpc
+ * requests (128k) to minimize overhead of smaller client requests.
+ *
+ * For example, fuse currently supports a maximum readdir buffer of 4k
+ * (regardless of the filesystem client's buffer size). readdir-ahead should
+ * effectively convert these smaller requests into fewer, larger sized requests
+ * for simple, sequential workloads (i.e., ls).
+ *
+ * The translator is currently designed to handle the simple, sequential case
+ * only. If a non-sequential directory read occurs, readdir-ahead disables
+ * preloads on the directory.
+ */
+
+#ifndef _CONFIG_H
+#define _CONFIG_H
+#include "config.h"
+#endif
+
+#include "glusterfs.h"
+#include "xlator.h"
+#include "call-stub.h"
+#include "readdir-ahead.h"
+#include "readdir-ahead-mem-types.h"
+#include "defaults.h"
+
+static int rda_fill_fd(call_frame_t *, xlator_t *, fd_t *);
+
+/*
+ * Get (or create) the fd context for storing prepopulated directory
+ * entries.
+ */
+static struct
+rda_fd_ctx *get_rda_fd_ctx(fd_t *fd, xlator_t *this)
+{
+	uint64_t val;
+	struct rda_fd_ctx *ctx;
+
+	LOCK(&fd->lock);
+
+	if (__fd_ctx_get(fd, this, &val) < 0) {
+		ctx = GF_CALLOC(1, sizeof(struct rda_fd_ctx),
+				gf_rda_mt_rda_fd_ctx);
+		if (!ctx)
+			goto out;
+
+		LOCK_INIT(&ctx->lock);
+		INIT_LIST_HEAD(&ctx->entries.list);
+		ctx->state = RDA_FD_NEW;
+		/* ctx offset values initialized to 0 */
+
+		if (__fd_ctx_set(fd, this, (uint64_t) ctx) < 0) {
+			GF_FREE(ctx);
+			ctx = NULL;
+			goto out;
+		}
+	} else {
+		ctx = (struct rda_fd_ctx *) val;
+	}
+out:
+	UNLOCK(&fd->lock);
+	return ctx;
+}
+
+/*
+ * Reset the tracking state of the context.
+ */
+static void
+rda_reset_ctx(struct rda_fd_ctx *ctx)
+{
+	ctx->state = RDA_FD_NEW;
+	ctx->cur_offset = 0;
+	ctx->cur_size = 0;
+	ctx->next_offset = 0;
+	gf_dirent_free(&ctx->entries);
+}
+
+/*
+ * Check whether we can handle a request. Offset verification is done by the
+ * caller, so we only check whether the preload buffer has completion status
+ * (including an error) or has some data to return.
+ */
+static gf_boolean_t
+rda_can_serve_readdirp(struct rda_fd_ctx *ctx, size_t request_size)
+{
+	if ((ctx->state & RDA_FD_EOD) ||
+	    (ctx->state & RDA_FD_ERROR) ||
+	    (!(ctx->state & RDA_FD_PLUGGED) && (ctx->cur_size > 0)))
+		return _gf_true;
+
+	return _gf_false;
+}
+
+/*
+ * Serve a request from the fd dentry list based on the size of the request
+ * buffer. ctx must be locked.
+ */
+static int32_t
+__rda_serve_readdirp(xlator_t *this, gf_dirent_t *entries, size_t request_size,
+		   struct rda_fd_ctx *ctx)
+{
+	gf_dirent_t *dirent, *tmp;
+	size_t dirent_size, size = 0;
+	int32_t count = 0;
+	struct rda_priv *priv = this->private;
+
+	list_for_each_entry_safe(dirent, tmp, &ctx->entries.list, list) {
+		dirent_size = gf_dirent_size(dirent->d_name);
+		if (size + dirent_size > request_size)
+			break;
+
+		size += dirent_size;
+		list_del_init(&dirent->list);
+		ctx->cur_size -= dirent_size;
+
+		list_add_tail(&dirent->list, &entries->list);
+		ctx->cur_offset = dirent->d_off;
+		count++;
+	}
+
+	if (ctx->cur_size <= priv->rda_low_wmark)
+		ctx->state |= RDA_FD_PLUGGED;
+
+	return count;
+}
+
+static int32_t
+rda_readdirp_stub(call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
+		  off_t offset, dict_t *xdata)
+{
+	gf_dirent_t entries;
+	int32_t ret;
+	struct rda_fd_ctx *ctx;
+	int op_errno = 0;
+
+	ctx = get_rda_fd_ctx(fd, this);
+	INIT_LIST_HEAD(&entries.list);
+	ret = __rda_serve_readdirp(this, &entries, size, ctx);
+
+	if (!ret && (ctx->state & RDA_FD_ERROR)) {
+		ret = -1;
+		op_errno = ctx->op_errno;
+		ctx->state &= ~RDA_FD_ERROR;
+
+		/*
+		 * the preload has stopped running in the event of an error, so
+		 * pass all future requests along
+		 */
+		ctx->state |= RDA_FD_BYPASS;
+	}
+
+	STACK_UNWIND_STRICT(readdirp, frame, ret, op_errno, &entries, xdata);
+	gf_dirent_free(&entries);
+
+	return 0;
+}
+
+static int32_t
+rda_readdirp(call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
+	     off_t off, dict_t *xdata)
+{
+	struct rda_fd_ctx *ctx;
+	call_stub_t *stub;
+	int fill = 0;
+
+	ctx = get_rda_fd_ctx(fd, this);
+	if (!ctx)
+		goto err;
+
+	if (ctx->state & RDA_FD_BYPASS)
+		goto bypass;
+
+	LOCK(&ctx->lock);
+
+	/* recheck now that we have the lock */
+	if (ctx->state & RDA_FD_BYPASS) {
+		UNLOCK(&ctx->lock);
+		goto bypass;
+	}
+
+	/*
+	 * If a new read comes in at offset 0 and the buffer has been
+	 * completed, reset the context and kickstart the filler again.
+	 */
+	if (!off && (ctx->state & RDA_FD_EOD) && (ctx->cur_size == 0)) {
+		rda_reset_ctx(ctx);
+		fill = 1;
+	}
+
+	/*
+	 * If a readdir occurs at an unexpected offset or we already have a
+	 * request pending, admit defeat and just get out of the way.
+	 */
+	if (off != ctx->cur_offset || ctx->stub) {
+		ctx->state |= RDA_FD_BYPASS;
+		UNLOCK(&ctx->lock);
+		goto bypass;
+	}
+
+	stub = fop_readdirp_stub(frame, rda_readdirp_stub, fd, size, off, xdata);
+	if (!stub) {
+		UNLOCK(&ctx->lock);
+		goto err;
+	}
+
+	/*
+	 * If we haven't bypassed the preload, this means we can either serve
+	 * the request out of the preload or the request that enables us to do
+	 * so is in flight...
+	 */
+	if (rda_can_serve_readdirp(ctx, size))
+		call_resume(stub);
+	else
+		ctx->stub = stub;
+
+	UNLOCK(&ctx->lock);
+
+	if (fill)
+		rda_fill_fd(frame, this, fd);
+
+	return 0;
+
+bypass:
+	STACK_WIND(frame, default_readdirp_cbk, FIRST_CHILD(this),
+		   FIRST_CHILD(this)->fops->readdirp, fd, size, off, xdata);
+	return 0;
+
+err:
+	STACK_UNWIND_STRICT(readdirp, frame, -1, ENOMEM, NULL, NULL);
+	return 0;
+}
+
+static int32_t
+rda_fill_fd_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
+		 int32_t op_ret, int32_t op_errno, gf_dirent_t *entries,
+		 dict_t *xdata)
+{
+	gf_dirent_t *dirent, *tmp;
+	struct rda_local *local = frame->local;
+	struct rda_fd_ctx *ctx = local->ctx;
+	struct rda_priv *priv = this->private;
+	int fill = 1;
+
+	LOCK(&ctx->lock);
+
+	/* Verify that the preload buffer is still pending on this data. */
+	if (ctx->next_offset != local->offset) {
+		gf_log(this->name, GF_LOG_ERROR,
+			"Out of sequence directory preload.");
+		ctx->state |= (RDA_FD_BYPASS|RDA_FD_ERROR);
+		ctx->op_errno = EUCLEAN;
+
+		goto out;
+	}
+
+	if (entries) {
+		list_for_each_entry_safe(dirent, tmp, &entries->list, list) {
+			list_del_init(&dirent->list);
+			/* must preserve entry order */
+			list_add_tail(&dirent->list, &ctx->entries.list);
+
+			ctx->cur_size += gf_dirent_size(dirent->d_name);
+			ctx->next_offset = dirent->d_off;
+		}
+	}
+
+	if (ctx->cur_size >= priv->rda_high_wmark)
+		ctx->state &= ~RDA_FD_PLUGGED;
+
+	if (!op_ret) {
+		/* we've hit eod */
+		ctx->state &= ~RDA_FD_RUNNING;
+		ctx->state |= RDA_FD_EOD;
+	} else if (op_ret == -1) {
+		/* kill the preload and pend the error */
+		ctx->state &= ~RDA_FD_RUNNING;
+		ctx->state |= RDA_FD_ERROR;
+		ctx->op_errno = op_errno;
+	}
+
+	/*
+	 * NOTE: The strict bypass logic in readdirp() means a pending request
+	 * is always based on ctx->cur_offset.
+	 */
+	if (ctx->stub &&
+	    rda_can_serve_readdirp(ctx, ctx->stub->args.size)) {
+		call_resume(ctx->stub);
+		ctx->stub = NULL;
+	}
+
+out:
+	/*
+	 * If we have been marked for bypass and have no pending stub, clear the
+	 * run state so we stop preloading the context with entries.
+	 */
+	if ((ctx->state & RDA_FD_BYPASS) && !ctx->stub)
+		ctx->state &= ~RDA_FD_RUNNING;
+
+	if (!(ctx->state & RDA_FD_RUNNING)) {
+		fill = 0;
+		STACK_DESTROY(ctx->fill_frame->root);
+		ctx->fill_frame = NULL;
+	}
+
+	UNLOCK(&ctx->lock);
+
+	if (fill)
+		rda_fill_fd(frame, this, local->fd);
+
+	return 0;
+}
+
+/*
+ * Start prepopulating the fd context with directory entries.
+ */
+static int
+rda_fill_fd(call_frame_t *frame, xlator_t *this, fd_t *fd)
+{
+	call_frame_t *nframe = NULL;
+	struct rda_local *local = NULL;
+	struct rda_fd_ctx *ctx;
+	off_t offset;
+	struct rda_priv *priv = this->private;
+
+	ctx = get_rda_fd_ctx(fd, this);
+	if (!ctx)
+		goto err;
+
+	LOCK(&ctx->lock);
+
+	if (ctx->state & RDA_FD_NEW) {
+		ctx->state &= ~RDA_FD_NEW;
+		ctx->state |= RDA_FD_RUNNING;
+		if (priv->rda_low_wmark)
+			ctx->state |= RDA_FD_PLUGGED;
+	}
+
+	offset = ctx->next_offset;
+
+	if (!ctx->fill_frame) {
+		nframe = copy_frame(frame);
+		if (!nframe) {
+			UNLOCK(&ctx->lock);
+			goto err;
+		}
+
+		local = mem_get0(this->local_pool);
+		if (!local) {
+			UNLOCK(&ctx->lock);
+			goto err;
+		}
+
+		local->ctx = ctx;
+		local->fd = fd;
+		nframe->local = local;
+
+		ctx->fill_frame = nframe;
+	} else {
+		nframe = ctx->fill_frame;
+		local = nframe->local;
+	}
+
+	local->offset = offset;
+
+	UNLOCK(&ctx->lock);
+
+	STACK_WIND(nframe, rda_fill_fd_cbk, FIRST_CHILD(this),
+		   FIRST_CHILD(this)->fops->readdirp, fd, priv->rda_req_size,
+		   offset, NULL);
+
+	return 0;
+
+err:
+	if (nframe)
+		FRAME_DESTROY(nframe);
+
+	return -1;
+}
+
+static int32_t
+rda_opendir_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
+		    int32_t op_ret, int32_t op_errno, fd_t *fd, dict_t *xdata)
+{
+	if (!op_ret)
+		rda_fill_fd(frame, this, fd);
+
+	STACK_UNWIND_STRICT(opendir, frame, op_ret, op_errno, fd, xdata);
+	return 0;
+}
+
+static int32_t
+rda_opendir(call_frame_t *frame, xlator_t *this, loc_t *loc, fd_t *fd,
+		dict_t *xdata)
+{
+	STACK_WIND(frame, rda_opendir_cbk, FIRST_CHILD(this),
+		   FIRST_CHILD(this)->fops->opendir, loc, fd, xdata);
+	return 0;
+}
+
+static int32_t
+rda_releasedir(xlator_t *this, fd_t *fd)
+{
+	uint64_t val;
+	struct rda_fd_ctx *ctx;
+
+	if (fd_ctx_del(fd, this, &val) < 0)
+		return -1;
+
+	ctx = (struct rda_fd_ctx *) val;
+	if (!ctx)
+		return 0;
+
+	rda_reset_ctx(ctx);
+
+	if (ctx->fill_frame)
+		STACK_DESTROY(ctx->fill_frame->root);
+
+	if (ctx->stub)
+		gf_log(this->name, GF_LOG_ERROR,
+			"released a directory with a pending stub");
+
+	GF_FREE(ctx);
+	return 0;
+}
+
+int32_t
+mem_acct_init(xlator_t *this)
+{
+	int ret = -1;
+
+	if (!this)
+		goto out;
+
+	ret = xlator_mem_acct_init(this, gf_rda_mt_end + 1);
+
+	if (ret != 0)
+		gf_log(this->name, GF_LOG_ERROR, "Memory accounting init"
+		       "failed");
+
+out:
+	return ret;
+}
+
+int
+reconfigure(xlator_t *this, dict_t *options)
+{
+	struct rda_priv *priv = this->private;
+
+	GF_OPTION_RECONF("rda-request-size", priv->rda_req_size, options,
+			 uint32, err);
+	GF_OPTION_RECONF("rda-low-wmark", priv->rda_low_wmark, options, size,
+			 err);
+	GF_OPTION_RECONF("rda-high-wmark", priv->rda_high_wmark, options, size,
+			 err);
+
+	return 0;
+err:
+	return -1;
+}
+
+int
+init(xlator_t *this)
+{
+	struct rda_priv *priv = NULL;
+
+        GF_VALIDATE_OR_GOTO("readdir-ahead", this, err);
+
+        if (!this->children || this->children->next) {
+                gf_log(this->name,  GF_LOG_ERROR,
+                        "FATAL: readdir-ahead not configured with exactly one"
+                        " child");
+                goto err;
+        }
+
+        if (!this->parents) {
+                gf_log(this->name, GF_LOG_WARNING,
+                        "dangling volume. check volfile ");
+        }
+
+	priv = GF_CALLOC(1, sizeof(struct rda_priv), gf_rda_mt_rda_priv);
+	if (!priv)
+		goto err;
+	this->private = priv;
+
+	this->local_pool = mem_pool_new(struct rda_local, 32);
+	if (!this->local_pool)
+		goto err;
+
+	GF_OPTION_INIT("rda-request-size", priv->rda_req_size, uint32, err);
+	GF_OPTION_INIT("rda-low-wmark", priv->rda_low_wmark, size, err);
+	GF_OPTION_INIT("rda-high-wmark", priv->rda_high_wmark, size, err);
+
+	return 0;
+
+err:
+	if (this->local_pool)
+		mem_pool_destroy(this->local_pool);
+	if (priv)
+		GF_FREE(priv);
+
+        return -1;
+}
+
+
+void
+fini(xlator_t *this)
+{
+        GF_VALIDATE_OR_GOTO ("readdir-ahead", this, out);
+
+	GF_FREE(this->private);
+
+out:
+        return;
+}
+
+struct xlator_fops fops = {
+	.opendir	= rda_opendir,
+	.readdirp	= rda_readdirp,
+};
+
+struct xlator_cbks cbks = {
+	.releasedir	= rda_releasedir,
+};
+
+struct volume_options options[] = {
+	{ .key = {"rda-request-size"},
+	  .type = GF_OPTION_TYPE_INT,
+	  .min = 4096,
+	  .max = 131072,
+	  .default_value = "131072",
+	  .description = "readdir-ahead request size",
+	},
+	{ .key = {"rda-low-wmark"},
+	  .type = GF_OPTION_TYPE_SIZET,
+	  .min = 0,
+	  .max = 10 * GF_UNIT_MB,
+	  .default_value = "4096",
+	  .description = "the value under which we plug",
+	},
+	{ .key = {"rda-high-wmark"},
+	  .type = GF_OPTION_TYPE_SIZET,
+	  .min = 0,
+	  .max = 100 * GF_UNIT_MB,
+	  .default_value = "131072",
+	  .description = "the value over which we unplug",
+	},
+        { .key = {NULL} },
+};
+
diff --git a/xlators/performance/readdir-ahead/src/readdir-ahead.h b/xlators/performance/readdir-ahead/src/readdir-ahead.h
new file mode 100644
index 00000000000..e48786daeca
--- /dev/null
+++ b/xlators/performance/readdir-ahead/src/readdir-ahead.h
@@ -0,0 +1,46 @@
+/*
+  Copyright (c) 2008-2013 Red Hat, Inc. <http://www.redhat.com>
+  This file is part of GlusterFS.
+
+  This file is licensed to you under your choice of the GNU Lesser
+  General Public License, version 3 or any later version (LGPLv3 or
+  later), or the GNU General Public License, version 2 (GPLv2), in all
+  cases as published by the Free Software Foundation.
+*/
+
+#ifndef __READDIR_AHEAD_H
+#define __READDIR_AHEAD_H
+
+/* state flags */
+#define RDA_FD_NEW	(1 << 0)
+#define RDA_FD_RUNNING	(1 << 1)
+#define RDA_FD_EOD	(1 << 2)
+#define RDA_FD_ERROR	(1 << 3)
+#define RDA_FD_BYPASS	(1 << 4)
+#define RDA_FD_PLUGGED	(1 << 5)
+
+struct rda_fd_ctx {
+	off_t cur_offset;	/* current head of the ctx */
+	size_t cur_size;	/* current size of the preload */
+	off_t next_offset;	/* tail of the ctx */
+	uint32_t state;
+	gf_lock_t lock;
+	gf_dirent_t entries;
+	call_frame_t *fill_frame;
+	call_stub_t *stub;
+	int op_errno;
+};
+
+struct rda_local {
+	struct rda_fd_ctx *ctx;
+	fd_t *fd;
+	off_t offset;
+};
+
+struct rda_priv {
+	uint32_t rda_req_size;
+	uint64_t rda_low_wmark;
+	uint64_t rda_high_wmark;
+};
+
+#endif /* __READDIR_AHEAD_H */