sys/vm/vm_swap.c

   1 /*
   2  * (MPSAFE)
   3  *
   4  * Copyright (c) 1982, 1986, 1989, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  *      @(#)vm_swap.c   8.5 (Berkeley) 2/17/94
  32  * $FreeBSD: src/sys/vm/vm_swap.c,v 1.96.2.2 2001/10/14 18:46:47 iedowse Exp $
  33  */
  34
  35 #include "opt_swap.h"
  36
  37 #include <sys/param.h>
  38 #include <sys/systm.h>
  39 #include <sys/sysproto.h>
  40 #include <sys/buf.h>
  41 #include <sys/proc.h>
  42 #include <sys/priv.h>
  43 #include <sys/nlookup.h>
  44 #include <sys/sysctl.h>
  45 #include <sys/dmap.h>           /* XXX */
  46 #include <sys/vnode.h>
  47 #include <sys/fcntl.h>
  48 #include <sys/blist.h>
  49 #include <sys/kernel.h>
  50 #include <sys/lock.h>
  51 #include <sys/conf.h>
  52 #include <sys/stat.h>
  53
  54 #include <vm/vm.h>
  55 #include <vm/vm_extern.h>
  56 #include <vm/swap_pager.h>
  57 #include <vm/vm_zone.h>
  58 #include <vm/vm_param.h>
  59
  60 #include <sys/thread2.h>
  61 #include <sys/mplock2.h>
  62 #include <sys/mutex2.h>
  63 #include <sys/spinlock2.h>
  64
  65 /*
  66  * Indirect driver for multi-controller paging.
  67  */
  68
  69 #ifndef NSWAPDEV
  70 #define NSWAPDEV        4
  71 #endif
  72 static struct swdevt should_be_malloced[NSWAPDEV];
  73 struct swdevt *swdevt = should_be_malloced;     /* exported to pstat/systat */
  74 static swblk_t nswap;           /* first block after the interleaved devs */
  75 static struct mtx swap_mtx = MTX_INITIALIZER("swpmtx");
  76 int nswdev = NSWAPDEV;                          /* exported to pstat/systat */
  77 int vm_swap_size;
  78 int vm_swap_max;
  79
  80 static int swapoff_one(int index);
  81 struct vnode *swapdev_vp;
  82
  83 /*
  84  * (struct vnode *a_vp, struct bio *b_bio)
  85  *
  86  * vn_strategy() for swapdev_vp.  Perform swap strategy interleave device
  87  * selection.
  88  *
  89  * No requirements.
  90  */
  91 static int
  92 swapdev_strategy(struct vop_strategy_args *ap)
  93 {
  94         struct bio *bio = ap->a_bio;
  95         struct bio *nbio;
  96         struct buf *bp = bio->bio_buf;
  97         int sz, off, seg, index, blkno, nblkno;
  98         struct swdevt *sp;
  99         sz = howmany(bp->b_bcount, PAGE_SIZE);
 100         blkno = (int)(bio->bio_offset >> PAGE_SHIFT);
 101
 102         /*
 103          * Convert interleaved swap into per-device swap.  Note that
 104          * the block size is left in PAGE_SIZE'd chunks (for the newswap)
 105          * here.
 106          */
 107         nbio = push_bio(bio);
 108         if (nswdev > 1) {
 109                 off = blkno % dmmax;
 110                 if (off + sz > dmmax) {
 111                         bp->b_error = EINVAL;
 112                         bp->b_flags |= B_ERROR;
 113                         biodone(bio);
 114                         return 0;
 115                 }
 116                 seg = blkno / dmmax;
 117                 index = seg % nswdev;
 118                 seg /= nswdev;
 119                 nbio->bio_offset = (off_t)(seg * dmmax + off) << PAGE_SHIFT;
 120         } else {
 121                 index = 0;
 122                 nbio->bio_offset = bio->bio_offset;
 123         }
 124         nblkno = (int)(nbio->bio_offset >> PAGE_SHIFT);
 125         sp = &swdevt[index];
 126         if (nblkno + sz > sp->sw_nblks) {
 127                 bp->b_error = EINVAL;
 128                 bp->b_flags |= B_ERROR;
 129                 /* I/O was never started on nbio, must biodone(bio) */
 130                 biodone(bio);
 131                 return 0;
 132         }
 133         if (sp->sw_vp == NULL) {
 134                 bp->b_error = ENODEV;
 135                 bp->b_flags |= B_ERROR;
 136                 /* I/O was never started on nbio, must biodone(bio) */
 137                 biodone(bio);
 138                 return 0;
 139         }
 140
 141         /*
 142          * Issue a strategy call on the appropriate swap vnode.  Note that
 143          * bp->b_vp is not modified.  Strategy code is always supposed to
 144          * use the passed vp.
 145          *
 146          * We have to use vn_strategy() here even if we know we have a
 147          * device in order to properly break up requests which exceed the
 148          * device's DMA limits.
 149          */
 150         vn_strategy(sp->sw_vp, nbio);
 151         return 0;
 152 }
 153
 154 static int
 155 swapdev_inactive(struct vop_inactive_args *ap)
 156 {
 157         vrecycle(ap->a_vp);
 158         return(0);
 159 }
 160
 161 static int
 162 swapdev_reclaim(struct vop_reclaim_args *ap)
 163 {
 164         return(0);
 165 }
 166
 167 /*
 168  * Create a special vnode op vector for swapdev_vp - we only use
 169  * vn_strategy(), everything else returns an error.
 170  */
 171 static struct vop_ops swapdev_vnode_vops = {
 172         .vop_default =          vop_defaultop,
 173         .vop_strategy =         swapdev_strategy,
 174         .vop_inactive =         swapdev_inactive,
 175         .vop_reclaim =          swapdev_reclaim
 176 };
 177 static struct vop_ops *swapdev_vnode_vops_p = &swapdev_vnode_vops;
 178
 179 VNODEOP_SET(swapdev_vnode_vops);
 180
 181 /*
 182  * swapon_args(char *name)
 183  *
 184  * System call swapon(name) enables swapping on device name,
 185  * which must be in the swdevsw.  Return EBUSY
 186  * if already swapping on this device.
 187  *
 188  * No requirements.
 189  */
 190 int
 191 sys_swapon(struct swapon_args *uap)
 192 {
 193         struct thread *td = curthread;
 194         struct vattr attr;
 195         struct vnode *vp;
 196         struct nlookupdata nd;
 197         int error;
 198
 199         error = priv_check(td, PRIV_ROOT);
 200         if (error)
 201                 return (error);
 202
 203         mtx_lock(&swap_mtx);
 204         get_mplock();
 205         vp = NULL;
 206         error = nlookup_init(&nd, uap->name, UIO_USERSPACE, NLC_FOLLOW);
 207         if (error == 0)
 208                 error = nlookup(&nd);
 209         if (error == 0)
 210                 error = cache_vref(&nd.nl_nch, nd.nl_cred, &vp);
 211         nlookup_done(&nd);
 212         if (error) {
 213                 rel_mplock();
 214                 mtx_unlock(&swap_mtx);
 215                 return (error);
 216         }
 217
 218         if (vn_isdisk(vp, &error)) {
 219                 error = swaponvp(td, vp, 0);
 220         } else if (vp->v_type == VREG && vp->v_tag == VT_NFS &&
 221                    (error = VOP_GETATTR(vp, &attr)) == 0) {
 222                 /*
 223                  * Allow direct swapping to NFS regular files in the same
 224                  * way that nfs_mountroot() sets up diskless swapping.
 225                  */
 226                 error = swaponvp(td, vp, attr.va_size / DEV_BSIZE);
 227         }
 228         if (error)
 229                 vrele(vp);
 230         rel_mplock();
 231         mtx_unlock(&swap_mtx);
 232
 233         return (error);
 234 }
 235
 236 /*
 237  * Swfree(index) frees the index'th portion of the swap map.
 238  * Each of the nswdev devices provides 1/nswdev'th of the swap
 239  * space, which is laid out with blocks of dmmax pages circularly
 240  * among the devices.
 241  *
 242  * The new swap code uses page-sized blocks.  The old swap code used
 243  * DEV_BSIZE'd chunks.
 244  *
 245  * XXX locking when multiple swapon's run in parallel
 246  */
 247 int
 248 swaponvp(struct thread *td, struct vnode *vp, u_quad_t nblks)
 249 {
 250         swblk_t aligned_nblks;
 251         int64_t dpsize;
 252         struct ucred *cred;
 253         struct swdevt *sp;
 254         swblk_t vsbase;
 255         swblk_t dvbase;
 256         cdev_t dev;
 257         int index;
 258         int error;
 259         swblk_t blk;
 260
 261         cred = td->td_ucred;
 262
 263         lwkt_gettoken(&vm_token);       /* needed for vm_swap_size and blist */
 264         mtx_lock(&swap_mtx);
 265
 266         if (!swapdev_vp) {
 267                 error = getspecialvnode(VT_NON, NULL, &swapdev_vnode_vops_p,
 268                                     &swapdev_vp, 0, 0);
 269                 if (error)
 270                         panic("Cannot get vnode for swapdev");
 271                 swapdev_vp->v_type = VNON;      /* Untyped */
 272                 vx_unlock(swapdev_vp);
 273         }
 274
 275         for (sp = swdevt, index = 0 ; index < nswdev; index++, sp++) {
 276                 if (sp->sw_vp == vp) {
 277                         error = EBUSY;
 278                         goto done;
 279                 }
 280                 if (!sp->sw_vp)
 281                         goto found;
 282
 283         }
 284         error = EINVAL;
 285         goto done;
 286     found:
 287         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 288         error = VOP_OPEN(vp, FREAD | FWRITE, cred, NULL);
 289         vn_unlock(vp);
 290         if (error)
 291                 goto done;
 292
 293         /*
 294          * v_rdev is not valid until after the VOP_OPEN() call.  dev_psize()
 295          * must be supported if a character device has been specified.
 296          */
 297         if (vp->v_type == VCHR)
 298                 dev = vp->v_rdev;
 299         else
 300                 dev = NULL;
 301
 302         if (nblks == 0 && dev != NULL) {
 303                 dpsize = dev_dpsize(dev);
 304                 if (dpsize == -1) {
 305                         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 306                         VOP_CLOSE(vp, FREAD | FWRITE, NULL);
 307                         vn_unlock(vp);
 308                         error = ENXIO;
 309                         goto done;
 310                 }
 311                 nblks = (u_quad_t)dpsize;
 312         }
 313         if (nblks == 0) {
 314                 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 315                 VOP_CLOSE(vp, FREAD | FWRITE, NULL);
 316                 vn_unlock(vp);
 317                 error = ENXIO;
 318                 goto done;
 319         }
 320
 321         /*
 322          * nblks is in DEV_BSIZE'd chunks, convert to PAGE_SIZE'd chunks.
 323          * First chop nblks off to page-align it, then convert.
 324          *
 325          * sw->sw_nblks is in page-sized chunks now too.
 326          */
 327         nblks &= ~(u_quad_t)(ctodb(1) - 1);
 328         nblks = dbtoc(nblks);
 329
 330         /*
 331          * Post-conversion nblks must not be >= BLIST_MAXBLKS, and
 332          * we impose a 4-swap-device limit so we have to divide it out
 333          * further.  Going beyond this will result in overflows in the
 334          * blist code.
 335          *
 336          * Post-conversion nblks must fit within a (swblk_t), which
 337          * this test also ensures.
 338          */
 339         if (nblks > BLIST_MAXBLKS / nswdev) {
 340                 kprintf("exceeded maximum of %d blocks per swap unit\n",
 341                         (int)BLIST_MAXBLKS / nswdev);
 342                 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 343                 VOP_CLOSE(vp, FREAD | FWRITE, NULL);
 344                 vn_unlock(vp);
 345                 error = ENXIO;
 346                 goto done;
 347         }
 348
 349         sp->sw_vp = vp;
 350         sp->sw_dev = dev2udev(dev);
 351         sp->sw_device = dev;
 352         sp->sw_flags = SW_FREED;
 353         sp->sw_nused = 0;
 354
 355         /*
 356          * nblks, nswap, and dmmax are PAGE_SIZE'd parameters now, not
 357          * DEV_BSIZE'd.   aligned_nblks is used to calculate the
 358          * size of the swap bitmap, taking into account the stripe size.
 359          */
 360         aligned_nblks = (swblk_t)((nblks + (dmmax - 1)) & ~(u_long)(dmmax - 1));
 361         sp->sw_nblks = aligned_nblks;
 362
 363         if (aligned_nblks * nswdev > nswap)
 364                 nswap = aligned_nblks * nswdev;
 365
 366         if (swapblist == NULL)
 367                 swapblist = blist_create(nswap);
 368         else
 369                 blist_resize(&swapblist, nswap, 0);
 370
 371         for (dvbase = dmmax; dvbase < aligned_nblks; dvbase += dmmax) {
 372                 blk = min(aligned_nblks - dvbase, dmmax);
 373                 vsbase = index * dmmax + dvbase * nswdev;
 374                 blist_free(swapblist, vsbase, blk);
 375                 vm_swap_size += blk;
 376                 vm_swap_max += blk;
 377         }
 378         swap_pager_newswap();
 379         error = 0;
 380 done:
 381         mtx_unlock(&swap_mtx);
 382         lwkt_reltoken(&vm_token);
 383         return (error);
 384 }
 385
 386 /*
 387  * swapoff_args(char *name)
 388  *
 389  * System call swapoff(name) disables swapping on device name,
 390  * which must be an active swap device. Return ENOMEM
 391  * if there is not enough memory to page in the contents of
 392  * the given device.
 393  *
 394  * No requirements.
 395  */
 396 int
 397 sys_swapoff(struct swapoff_args *uap)
 398 {
 399         struct vnode *vp;
 400         struct nlookupdata nd;
 401         struct swdevt *sp;
 402         int error, index;
 403
 404         error = priv_check(curthread, PRIV_ROOT);
 405         if (error)
 406                 return (error);
 407
 408         mtx_lock(&swap_mtx);
 409         get_mplock();
 410         vp = NULL;
 411         error = nlookup_init(&nd, uap->name, UIO_USERSPACE, NLC_FOLLOW);
 412         if (error == 0)
 413                 error = nlookup(&nd);
 414         if (error == 0)
 415                 error = cache_vref(&nd.nl_nch, nd.nl_cred, &vp);
 416         nlookup_done(&nd);
 417         if (error)
 418                 goto done;
 419
 420         for (sp = swdevt, index = 0; index < nswdev; index++, sp++) {
 421                 if (sp->sw_vp == vp)
 422                         goto found;
 423         }
 424         error = EINVAL;
 425         goto done;
 426 found:
 427         error = swapoff_one(index);
 428         swap_pager_newswap();
 429
 430 done:
 431         rel_mplock();
 432         mtx_unlock(&swap_mtx);
 433         return (error);
 434 }
 435
 436 static int
 437 swapoff_one(int index)
 438 {
 439         swblk_t blk, aligned_nblks;
 440         swblk_t dvbase, vsbase;
 441         u_int pq_active_clean, pq_inactive_clean;
 442         struct swdevt *sp;
 443         struct vm_page marker;
 444         vm_page_t m;
 445         int q;
 446
 447         mtx_lock(&swap_mtx);
 448
 449         sp = &swdevt[index];
 450         aligned_nblks = sp->sw_nblks;
 451         pq_active_clean = pq_inactive_clean = 0;
 452
 453         /*
 454          * We can turn off this swap device safely only if the
 455          * available virtual memory in the system will fit the amount
 456          * of data we will have to page back in, plus an epsilon so
 457          * the system doesn't become critically low on swap space.
 458          */
 459         for (q = 0; q < PQ_L2_SIZE; ++q) {
 460                 bzero(&marker, sizeof(marker));
 461                 marker.flags = PG_BUSY | PG_FICTITIOUS | PG_MARKER;
 462                 marker.queue = PQ_ACTIVE + q;
 463                 marker.pc = q;
 464                 marker.wire_count = 1;
 465
 466                 vm_page_queues_spin_lock(marker.queue);
 467                 TAILQ_INSERT_HEAD(&vm_page_queues[marker.queue].pl,
 468                                   &marker, pageq);
 469
 470                 while ((m = TAILQ_NEXT(&marker, pageq)) != NULL) {
 471                         TAILQ_REMOVE(&vm_page_queues[marker.queue].pl,
 472                                      &marker, pageq);
 473                         TAILQ_INSERT_AFTER(&vm_page_queues[marker.queue].pl, m,
 474                                            &marker, pageq);
 475                         if (m->flags & (PG_MARKER | PG_FICTITIOUS))
 476                                 continue;
 477
 478                         if (vm_page_busy_try(m, FALSE) == 0) {
 479                                 vm_page_queues_spin_unlock(marker.queue);
 480                                 if (m->dirty == 0) {
 481                                         vm_page_test_dirty(m);
 482                                         if (m->dirty == 0)
 483                                                 ++pq_active_clean;
 484                                 }
 485                                 vm_page_wakeup(m);
 486                                 vm_page_queues_spin_lock(marker.queue);
 487                         }
 488                 }
 489                 TAILQ_REMOVE(&vm_page_queues[marker.queue].pl, &marker, pageq);
 490                 vm_page_queues_spin_unlock(marker.queue);
 491
 492                 marker.queue = PQ_INACTIVE + q;
 493                 marker.pc = q;
 494                 vm_page_queues_spin_lock(marker.queue);
 495                 TAILQ_INSERT_HEAD(&vm_page_queues[marker.queue].pl,
 496                                   &marker, pageq);
 497
 498                 while ((m = TAILQ_NEXT(&marker, pageq)) != NULL) {
 499                         TAILQ_REMOVE(
 500                                 &vm_page_queues[marker.queue].pl,
 501                                 &marker, pageq);
 502                         TAILQ_INSERT_AFTER(
 503                                 &vm_page_queues[marker.queue].pl,
 504                                 m, &marker, pageq);
 505                         if (m->flags & (PG_MARKER | PG_FICTITIOUS))
 506                                 continue;
 507
 508                         if (vm_page_busy_try(m, FALSE) == 0) {
 509                                 vm_page_queues_spin_unlock(marker.queue);
 510                                 if (m->dirty == 0) {
 511                                         vm_page_test_dirty(m);
 512                                         if (m->dirty == 0)
 513                                                 ++pq_inactive_clean;
 514                                 }
 515                                 vm_page_wakeup(m);
 516                                 vm_page_queues_spin_lock(marker.queue);
 517                         }
 518                 }
 519                 TAILQ_REMOVE(&vm_page_queues[marker.queue].pl,
 520                              &marker, pageq);
 521                 vm_page_queues_spin_unlock(marker.queue);
 522         }
 523
 524         if (vmstats.v_free_count + vmstats.v_cache_count + pq_active_clean +
 525             pq_inactive_clean + vm_swap_size < aligned_nblks + nswap_lowat) {
 526                 mtx_unlock(&swap_mtx);
 527                 return (ENOMEM);
 528         }
 529
 530         /*
 531          * Prevent further allocations on this device
 532          */
 533         sp->sw_flags |= SW_CLOSING;
 534         for (dvbase = dmmax; dvbase < aligned_nblks; dvbase += dmmax) {
 535                 blk = min(aligned_nblks - dvbase, dmmax);
 536                 vsbase = index * dmmax + dvbase * nswdev;
 537                 vm_swap_size -= blist_fill(swapblist, vsbase, blk);
 538                 vm_swap_max -= blk;
 539         }
 540
 541         /*
 542          * Page in the contents of the device and close it.
 543          */
 544         if (swap_pager_swapoff(index) && swap_pager_swapoff(index)) {
 545                 mtx_unlock(&swap_mtx);
 546                 return (EINTR);
 547         }
 548
 549         vn_lock(sp->sw_vp, LK_EXCLUSIVE | LK_RETRY);
 550         VOP_CLOSE(sp->sw_vp, FREAD | FWRITE, NULL);
 551         vn_unlock(sp->sw_vp);
 552         vrele(sp->sw_vp);
 553         bzero(swdevt + index, sizeof(struct swdevt));
 554
 555         /*
 556          * Resize the bitmap based on the nem largest swap device,
 557          * or free the bitmap if there are no more devices.
 558          */
 559         for (sp = swdevt, aligned_nblks = 0; sp < swdevt + nswdev; sp++) {
 560                 if (sp->sw_vp)
 561                         aligned_nblks = max(aligned_nblks, sp->sw_nblks);
 562         }
 563
 564         nswap = aligned_nblks * nswdev;
 565
 566         if (nswap == 0) {
 567                 blist_destroy(swapblist);
 568                 swapblist = NULL;
 569                 vrele(swapdev_vp);
 570                 swapdev_vp = NULL;
 571         } else {
 572                 blist_resize(&swapblist, nswap, 0);
 573         }
 574
 575         mtx_unlock(&swap_mtx);
 576         return (0);
 577 }
 578
 579 /*
 580  * Account for swap space in individual swdevt's.  The caller ensures
 581  * that the provided range falls into a single swdevt.
 582  *
 583  * +count       space freed
 584  * -count       space allocated
 585  */
 586 void
 587 swapacctspace(swblk_t base, swblk_t count)
 588 {
 589         int index;
 590         int seg;
 591
 592         vm_swap_size += count;
 593         seg = base / dmmax;
 594         index = seg % nswdev;
 595         swdevt[index].sw_nused -= count;
 596 }
 597
 598 /*
 599  * Retrieve swap info
 600  */
 601 static int
 602 sysctl_vm_swap_info(SYSCTL_HANDLER_ARGS)
 603 {
 604         struct xswdev xs;
 605         struct swdevt *sp;
 606         int     error;
 607         int     n;
 608
 609         error = 0;
 610         for (n = 0; n < nswdev; ++n) {
 611                 sp = &swdevt[n];
 612
 613                 xs.xsw_size = sizeof(xs);
 614                 xs.xsw_version = XSWDEV_VERSION;
 615                 xs.xsw_blksize = PAGE_SIZE;
 616                 xs.xsw_dev = sp->sw_dev;
 617                 xs.xsw_flags = sp->sw_flags;
 618                 xs.xsw_nblks = sp->sw_nblks;
 619                 xs.xsw_used = sp->sw_nused;
 620
 621                 error = SYSCTL_OUT(req, &xs, sizeof(xs));
 622                 if (error)
 623                         break;
 624         }
 625         return (error);
 626 }
 627
 628 SYSCTL_INT(_vm, OID_AUTO, nswapdev, CTLFLAG_RD, &nswdev, 0,
 629            "Number of swap devices");
 630 SYSCTL_NODE(_vm, OID_AUTO, swap_info_array, CTLFLAG_RD, sysctl_vm_swap_info,
 631             "Swap statistics by device");