summaryrefslogtreecommitdiffstats
path: root/xlators/performance/readdir-ahead/src/readdir-ahead.c
blob: 4b57a8b1c3fb2f3e670748c9ec5926ef3bbc04fe (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
/*
  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.
 */

#include "glusterfs.h"
#include "xlator.h"
#include "call-stub.h"
#include "readdir-ahead.h"
#include "readdir-ahead-mem-types.h"
#include "defaults.h"
#include "readdir-ahead-messages.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 */
                ctx->xattrs = NULL;

		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;
        ctx->op_errno = 0;
	gf_dirent_free(&ctx->entries);
        if (ctx->xattrs) {
                dict_unref (ctx->xattrs);
                ctx->xattrs = NULL;
        }
}

/*
 * 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)) ||
            (request_size && ctx->cur_size >= request_size))
		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, inodectx_size = 0;
	int32_t          count             = 0;
	struct rda_priv *priv              = NULL;

        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;

                inodectx_size = 0;

                inode_ctx_del (dirent->inode, this, (void *)&inodectx_size);

		size += dirent_size;
		list_del_init(&dirent->list);
		ctx->cur_size -= dirent_size;

                priv->rda_cache_size -= (dirent_size + inodectx_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;
		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;
	}

        /*
         * Use the op_errno sent by lower layers as xlators above will check
         * the op_errno for identifying whether readdir is completed or not.
         */
        op_errno = ctx->op_errno;

	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);
                /*
                 * Unref and discard the 'list of xattrs to be fetched'
                 * stored during opendir call. This is done above - inside
                 * rda_reset_ctx().
                 * Now, ref the xdata passed by md-cache in actual readdirp()
                 * call and use that for all subsequent internal readdirp()
                 * requests issued by this xlator.
                 */
                ctx->xattrs = dict_ref (xdata);
		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;

                if (!(ctx->state & RDA_FD_RUNNING)) {
                        fill = 1;
                        ctx->state |= RDA_FD_RUNNING;
                }
        }

	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;
        size_t inodectx_size = 0, dirent_size = 0;

	LOCK(&ctx->lock);

	/* Verify that the preload buffer is still pending on this data. */
	if (ctx->next_offset != local->offset) {
		gf_msg(this->name, GF_LOG_ERROR,
                       0, READDIR_AHEAD_MSG_OUT_OF_SEQUENCE,
                       "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);

                        dirent_size = gf_dirent_size (dirent->d_name);
                        inodectx_size = 0;

                        if (dirent->inode) {
                                inodectx_size = inode_ctx_size (dirent->inode);
                                inode_ctx_set (dirent->inode, this,
                                               (void *)inodectx_size);
                        }

			ctx->cur_size += dirent_size;

                        priv->rda_cache_size += (dirent_size + inodectx_size);

			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;
                ctx->op_errno = op_errno;
	} 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->stub && ((ctx->state & RDA_FD_BYPASS)
                           || (priv->rda_cache_size > priv->rda_cache_limit)))
		ctx->state &= ~RDA_FD_RUNNING;

	if (!(ctx->state & RDA_FD_RUNNING)) {
		fill = 0;
                if (ctx->xattrs) {
                        /*
                         * fill = 0 and hence rda_fill_fd() won't be invoked.
                         * unref for ref taken in rda_fill_fd()
                         */
                        dict_unref (ctx->xattrs);
                        ctx->xattrs = NULL;
                }

		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_local *orig_local = frame->local;
	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;

                if (!ctx->xattrs && orig_local && orig_local->xattrs) {
                        /* when this function is invoked by rda_opendir_cbk */
                        ctx->xattrs = dict_ref(orig_local->xattrs);
                }
	} 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, ctx->xattrs);

	return 0;

err:
	if (nframe)
		FRAME_DESTROY(nframe);

	return -1;
}


static int
rda_unpack_mdc_loaded_keys_to_dict(char *payload, dict_t *dict)
{
        int      ret = -1;
        char    *mdc_key = NULL;

        if (!payload || !dict) {
                goto out;
        }

        mdc_key = strtok(payload, " ");
        while (mdc_key != NULL) {
                ret = dict_set_int8 (dict, mdc_key, 0);
                if (ret) {
                        goto out;
                }
                mdc_key = strtok(NULL, " ");
        }

out:
        return ret;
}


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)
{
        struct rda_local *local = frame->local;

	if (!op_ret)
		rda_fill_fd(frame, this, fd);

        frame->local = NULL;

	STACK_UNWIND_STRICT(opendir, frame, op_ret, op_errno, fd, xdata);

        if (local && local->xattrs) {
                /* unref for dict_new() done in rda_opendir */
                dict_unref (local->xattrs);
                local->xattrs = NULL;
        }

        if (local)
                mem_put (local);

	return 0;
}

static int32_t
rda_opendir(call_frame_t *frame, xlator_t *this, loc_t *loc, fd_t *fd,
		dict_t *xdata)
{
        int                  ret = -1;
        int                  op_errno = 0;
        char                *payload = NULL;
        struct rda_local    *local = NULL;
        dict_t              *xdata_from_req = NULL;

        if (xdata) {
                /*
                 * Retrieve list of keys set by md-cache xlator and store it
                 * in local to be consumed in rda_opendir_cbk
                 */
                ret = dict_get_str (xdata, GF_MDC_LOADED_KEY_NAMES, &payload);
                if (ret)
                        goto wind;

                xdata_from_req = dict_new();
                if (!xdata_from_req) {
                        op_errno = ENOMEM;
                        goto unwind;
                }

                ret = rda_unpack_mdc_loaded_keys_to_dict((char *) payload,
                                                         xdata_from_req);
                if (ret) {
                        dict_unref(xdata_from_req);
                        goto wind;
                }

                local = mem_get0(this->local_pool);
                if (!local) {
                        dict_unref(xdata_from_req);
                        op_errno = ENOMEM;
                        goto unwind;
                }

                local->xattrs = xdata_from_req;
                frame->local = local;
        }

wind:
        if (xdata)
                /* Remove the key after consumption. */
                dict_del (xdata, GF_MDC_LOADED_KEY_NAMES);

        STACK_WIND(frame, rda_opendir_cbk, FIRST_CHILD(this),
                   FIRST_CHILD(this)->fops->opendir, loc, fd, xdata);
        return 0;

unwind:
        STACK_UNWIND_STRICT(opendir, frame, -1, op_errno, 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_msg(this->name, GF_LOG_ERROR, 0,
		        READDIR_AHEAD_MSG_DIR_RELEASE_PENDING_STUB,
                       "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_msg(this->name, GF_LOG_ERROR, ENOMEM,
                       READDIR_AHEAD_MSG_NO_MEMORY, "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,
			 size_uint64, err);
	GF_OPTION_RECONF("rda-low-wmark", priv->rda_low_wmark, options,
                         size_uint64, err);
	GF_OPTION_RECONF("rda-high-wmark", priv->rda_high_wmark, options,
                         size_uint64, err);
        GF_OPTION_RECONF("rda-cache-limit", priv->rda_cache_limit, options,
                         size_uint64, 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_msg(this->name,  GF_LOG_ERROR, 0,
                        READDIR_AHEAD_MSG_XLATOR_CHILD_MISCONFIGURED,
                        "FATAL: readdir-ahead not configured with exactly one"
                        " child");
                goto err;
        }

        if (!this->parents) {
                gf_msg(this->name, GF_LOG_WARNING, 0,
                        READDIR_AHEAD_MSG_VOL_MISCONFIGURED,
                        "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, size_uint64,
                       err);
	GF_OPTION_INIT("rda-low-wmark", priv->rda_low_wmark, size_uint64, err);
	GF_OPTION_INIT("rda-high-wmark", priv->rda_high_wmark, size_uint64,
                       err);
        GF_OPTION_INIT("rda-cache-limit", priv->rda_cache_limit, size_uint64,
                       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_SIZET,
	  .min = 4096,
	  .max = 131072,
	  .default_value = "128KB",
	  .description = "size of buffer in readdirp calls initiated by "
                         "readdir-ahead ",
	},
	{ .key = {"rda-low-wmark"},
	  .type = GF_OPTION_TYPE_SIZET,
	  .min = 0,
	  .max = 10 * GF_UNIT_MB,
	  .default_value = "4096",
	  .description = "the value under which readdir-ahead plugs",
	},
	{ .key = {"rda-high-wmark"},
	  .type = GF_OPTION_TYPE_SIZET,
	  .min = 0,
	  .max = 100 * GF_UNIT_MB,
	  .default_value = "128KB",
	  .description = "the value over which readdir-ahead unplugs",
	},
        { .key = {"rda-cache-limit"},
          .type = GF_OPTION_TYPE_SIZET,
          .min = 0,
          .max = 1 * GF_UNIT_GB,
          .default_value = "10MB",
          .description = "maximum size of cache consumed by readdir-ahead "
                         "xlator. This value is global and total memory "
                         "consumption by readdir-ahead is capped by this "
                         "value, irrespective of the number/size of "
                         "directories cached",
        },
        { .key = {NULL} },
};