Merge commit '0b2e8253986c5c761129b58cfdac46d204903de1'

[unleashed.git] / kernel / vm / vpm.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */


/*
 * VM - generic vnode page mapping interfaces.
 *
 * Mechanism to provide temporary mappings to vnode pages.
 * The typical use would be to copy/access file data.
 */

#include <sys/types.h>
#include <sys/t_lock.h>
#include <sys/param.h>
#include <sys/sysmacros.h>
#include <sys/buf.h>
#include <sys/systm.h>
#include <sys/vnode.h>
#include <sys/mman.h>
#include <sys/errno.h>
#include <sys/cred.h>
#include <sys/kmem.h>
#include <sys/vtrace.h>
#include <sys/cmn_err.h>
#include <sys/debug.h>
#include <sys/thread.h>
#include <sys/dumphdr.h>
#include <sys/bitmap.h>
#include <sys/lgrp.h>

#include <vm/seg_kmem.h>
#include <vm/hat.h>
#include <vm/as.h>
#include <vm/seg.h>
#include <vm/seg_kpm.h>
#include <vm/seg_map.h>
#include <vm/page.h>
#include <vm/pvn.h>
#include <vm/rm.h>
#include <vm/vpm.h>


#ifdef  SEGKPM_SUPPORT
/*
 * VPM can be disabled by setting vpm_enable = 0 in
 * /etc/system.
 *
 */
int vpm_enable = 1;

#else

int vpm_enable = 0;

#endif

#ifdef  SEGKPM_SUPPORT


int     vpm_cache_enable = 1;
long    vpm_cache_percent = 12;
long    vpm_cache_size;
int     vpm_nfreelist = 0;
int     vpmd_freemsk = 0;

#define VPM_S_PAD       64
union vpm_cpu {
        struct {
                int     vcpu_free_ndx;
                ulong_t vcpu_hits;
                ulong_t vcpu_misses;
        } vcpu;
        char vpm_pad[VPM_S_PAD];
};
static union vpm_cpu    *vpmd_cpu;

#define vfree_ndx       vcpu.vcpu_free_ndx

int     vpm_cachemode = VPMCACHE_LRU;

#define PPMTX(pp) (&(pp)->p_ilock)

static struct vpmap *vpmd_vpmap;        /* list of vpmap structs preallocated */
static struct vpmfree *vpmd_free;
#define VPMAPMTX(vpm)   (&vpm->vpm_mtx)
#define VPMAP2VMF(vpm)  (&vpmd_free[(vpm - vpmd_vpmap) & vpmd_freemsk])
#define VPMAP2VMF_NDX(vpm)      (ushort_t)((vpm - vpmd_vpmap) & vpmd_freemsk)
#define VPMP(id)        (&vpmd_vpmap[id - 1])
#define VPMID(vpm)      (uint_t)((vpm - vpmd_vpmap) + 1)


#ifdef  DEBUG

struct  vpm_debug {
        int vpmd_steals;
        int vpmd_contend;
        int vpmd_prevpagelocked;
        int vpmd_getpagefailed;
        int vpmd_zerostart;
        int vpmd_emptyfreelist;
        int vpmd_nofreevpms;
} vpm_debug;

#define VPM_DEBUG(x)    ((vpm_debug.x)++)

int     steals;
int     steals_mtbf = 7;
int     contend;
int     contend_mtbf = 127;

#define VPM_MTBF(v, f)  (((++(v)) & (f)) != (f))

#else   /* DEBUG */

#define VPM_MTBF(v, f)  (1)
#define VPM_DEBUG(x)    /* nothing */

#endif

/*
 * The vpm cache.
 *
 * The main purpose of having a cache here is to speed up page_lookup()
 * operations and also provide an LRU(default) behaviour of file pages. The
 * page_lookup() operation tends to be expensive if a page has to be
 * reclaimed from the system page cache("cachelist"). Once we speed up the
 * page_lookup()->page_reclaim() path then there there should be no need for
 * this cache. The system page cache(cachelist) should effectively serve the
 * purpose of caching file pages.
 *
 * This cache is very similar to segmap's smap cache. Each page in the
 * cache is tracked by the structure vpmap_t. But unlike segmap, there is no
 * hash table. The page_t has a reference to the vpmap_t when cached. For a
 * given vnode, offset the page is found by means of a page_lookup() operation.
 * Any page which has a mapping(i.e when cached) will not be in the
 * system 'cachelist'. Hence the page_lookup() will not have to do a
 * page_reclaim(). That is how the cache serves to speed up page_lookup()
 * operations.
 *
 * This cache can be disabled by setting vpm_cache_enable = 0 in /etc/system.
 */

void
vpm_init()
{
        long  npages;
        struct vpmap *vpm;
        struct vpmfree *vpmflp;
        int i, ndx;
        extern void prefetch_smap_w(void *);

        if (!kpm_enable) {
                vpm_enable = 0;
        }

        if (!vpm_enable || !vpm_cache_enable) {
                return;
        }

        /*
         * Set the size of the cache.
         */
        vpm_cache_size = mmu_ptob((physmem * vpm_cache_percent)/100);
        if (vpm_cache_size < VPMAP_MINCACHE) {
                vpm_cache_size = VPMAP_MINCACHE;
        }

        if (vpm_cache_size > VPMAP_MAXCACHE) {
                vpm_cache_size = VPMAP_MAXCACHE;
        }

        /*
         * Number of freelists.
         */
        if (vpm_nfreelist == 0) {
                vpm_nfreelist = max_ncpus;
        } else if (vpm_nfreelist < 0 || vpm_nfreelist > 2 * max_ncpus) {
                cmn_err(CE_WARN, "vpmap create : number of freelist "
                "vpm_nfreelist %d using %d", vpm_nfreelist, max_ncpus);
                vpm_nfreelist = 2 * max_ncpus;
        }

        /*
         * Round it up to the next power of 2
         */
        if (!ISP2(vpm_nfreelist)) {
                vpm_nfreelist = 1 << (highbit(vpm_nfreelist));
        }
        vpmd_freemsk = vpm_nfreelist - 1;

        /*
         * Use a per cpu rotor index to spread the allocations evenly
         * across the available vpm freelists.
         */
        vpmd_cpu = kmem_zalloc(sizeof (union vpm_cpu) * max_ncpus, KM_SLEEP);
        ndx = 0;
        for (i = 0; i < max_ncpus; i++) {

                vpmd_cpu[i].vfree_ndx = ndx;
                ndx = (ndx + 1) & vpmd_freemsk;
        }

        /*
         * Allocate and initialize the freelist.
         */
        vpmd_free = kmem_zalloc(vpm_nfreelist * sizeof (struct vpmfree),
            KM_SLEEP);
        for (i = 0; i < vpm_nfreelist; i++) {

                vpmflp = &vpmd_free[i];
                /*
                 * Set up initial queue pointers. They will get flipped
                 * back and forth.
                 */
                vpmflp->vpm_allocq = &vpmflp->vpm_freeq[VPMALLOCQ];
                vpmflp->vpm_releq = &vpmflp->vpm_freeq[VPMRELEQ];
        }

        npages = mmu_btop(vpm_cache_size);


        /*
         * Allocate and initialize the vpmap structs. We need to
         * walk the array backwards as the prefetch happens in reverse
         * order.
         */
        vpmd_vpmap = kmem_alloc(sizeof (struct vpmap) * npages, KM_SLEEP);
        for (vpm = &vpmd_vpmap[npages - 1]; vpm >= vpmd_vpmap; vpm--) {
                struct vpmfree *vpmflp;
                union vpm_freeq *releq;
                struct vpmap *vpmapf;

                /*
                 * Use prefetch as we have to walk thru a large number of
                 * these data structures. We just use the smap's prefetch
                 * routine as it does the same.
                 */
                prefetch_smap_w((void *)vpm);

                vpm->vpm_vp = NULL;
                vpm->vpm_off = 0;
                vpm->vpm_pp = NULL;
                vpm->vpm_refcnt = 0;
                mutex_init(&vpm->vpm_mtx, NULL, MUTEX_DEFAULT, NULL);
                vpm->vpm_free_ndx = VPMAP2VMF_NDX(vpm);

                vpmflp = VPMAP2VMF(vpm);
                releq = vpmflp->vpm_releq;

                vpmapf = releq->vpmq_free;
                if (vpmapf == NULL) {
                        releq->vpmq_free = vpm->vpm_next = vpm->vpm_prev = vpm;
                } else {
                        vpm->vpm_next = vpmapf;
                        vpm->vpm_prev = vpmapf->vpm_prev;
                        vpmapf->vpm_prev = vpm;
                        vpm->vpm_prev->vpm_next = vpm;
                        releq->vpmq_free = vpm->vpm_next;
                }

                /*
                 * Indicate that the vpmap is on the releq at start
                 */
                vpm->vpm_ndxflg = VPMRELEQ;
        }
}


/*
 * unhooks vpm from the freelist if it is still on the freelist.
 */
#define VPMAP_RMFREELIST(vpm) \
        { \
                if (vpm->vpm_next != NULL) { \
                        union vpm_freeq *freeq; \
                        struct vpmfree *vpmflp; \
                        vpmflp = &vpmd_free[vpm->vpm_free_ndx]; \
                        freeq = &vpmflp->vpm_freeq[vpm->vpm_ndxflg]; \
                        mutex_enter(&freeq->vpmq_mtx); \
                        if (freeq->vpmq_free != vpm) { \
                                vpm->vpm_prev->vpm_next = vpm->vpm_next; \
                                vpm->vpm_next->vpm_prev = vpm->vpm_prev; \
                        } else if (vpm == vpm->vpm_next) { \
                                freeq->vpmq_free = NULL; \
                        } else { \
                                freeq->vpmq_free = vpm->vpm_next; \
                                vpm->vpm_prev->vpm_next = vpm->vpm_next; \
                                vpm->vpm_next->vpm_prev = vpm->vpm_prev; \
                        } \
                        mutex_exit(&freeq->vpmq_mtx); \
                        vpm->vpm_next = vpm->vpm_prev = NULL; \
                } \
        }

static int
get_freelndx(int mode)
{
        int ndx;

        ndx = vpmd_cpu[CPU->cpu_seqid].vfree_ndx & vpmd_freemsk;
        switch (mode) {

        case    VPMCACHE_LRU:
        default:
                        vpmd_cpu[CPU->cpu_seqid].vfree_ndx++;
                        break;
        }
        return (ndx);
}


/*
 * Find one vpmap structure from the free lists and use it for the newpage.
 * The previous page it cached is dissociated and released. The page_t's
 * p_vpmref is cleared only when the vpm it is pointing to is locked(or
 * for AMD64 when the page is exclusively locked in page_unload. That is
 * because the p_vpmref is treated as mapping).
 *
 * The page's p_vpmref is set when the page is
 * locked(at least SHARED locked).
 */
static struct vpmap *
get_free_vpmap(page_t *newpage)
{
        struct vpmfree *vpmflp;
        kmutex_t *vmtx;
        struct vpmap *vpm, *first;
        union vpm_freeq *allocq, *releq;
        page_t *pp = NULL;
        int end_ndx, page_locked = 0;
        int free_ndx;

        /*
         * get the freelist bin index.
         */
        free_ndx = get_freelndx(vpm_cachemode);

        end_ndx = free_ndx;
        vpmflp = &vpmd_free[free_ndx];

retry_queue:
        allocq = vpmflp->vpm_allocq;
        mutex_enter(&allocq->vpmq_mtx);

        if ((vpm = allocq->vpmq_free) == NULL) {

skip_queue:
                /*
                 * The alloc list is empty or this queue is being skipped;
                 * first see if the allocq toggled.
                 */
                if (vpmflp->vpm_allocq != allocq) {
                        /* queue changed */
                        mutex_exit(&allocq->vpmq_mtx);
                        goto retry_queue;
                }
                releq = vpmflp->vpm_releq;
                if (!mutex_tryenter(&releq->vpmq_mtx)) {
                        /* cannot get releq; a free vpmap may be there now */
                        mutex_exit(&allocq->vpmq_mtx);

                        /*
                         * This loop could spin forever if this thread has
                         * higher priority than the thread that is holding
                         * releq->vpmq_mtx. In order to force the other thread
                         * to run, we'll lock/unlock the mutex which is safe
                         * since we just unlocked the allocq mutex.
                         */
                        mutex_enter(&releq->vpmq_mtx);
                        mutex_exit(&releq->vpmq_mtx);
                        goto retry_queue;
                }
                if (releq->vpmq_free == NULL) {
                        VPM_DEBUG(vpmd_emptyfreelist);
                        /*
                         * This freelist is empty.
                         * This should not happen unless clients
                         * are failing to release the vpmap after
                         * accessing the data. Before resorting
                         * to sleeping, try the next list of the same color.
                         */
                        free_ndx = (free_ndx + 1) & vpmd_freemsk;
                        if (free_ndx != end_ndx) {
                                mutex_exit(&releq->vpmq_mtx);
                                mutex_exit(&allocq->vpmq_mtx);
                                vpmflp = &vpmd_free[free_ndx];
                                goto retry_queue;
                        }
                        /*
                         * Tried all freelists.
                         * wait on this list and hope something gets freed.
                         */
                        vpmflp->vpm_want++;
                        mutex_exit(&vpmflp->vpm_freeq[1].vpmq_mtx);
                        cv_wait(&vpmflp->vpm_free_cv,
                            &vpmflp->vpm_freeq[0].vpmq_mtx);
                        vpmflp->vpm_want--;
                        mutex_exit(&vpmflp->vpm_freeq[0].vpmq_mtx);
                        vpmflp = &vpmd_free[free_ndx];
                        VPM_DEBUG(vpmd_nofreevpms);
                        goto retry_queue;
                } else {
                        /*
                         * Something on the rele queue; flip the alloc
                         * and rele queues and retry.
                         */
                        vpmflp->vpm_allocq = releq;
                        vpmflp->vpm_releq = allocq;
                        mutex_exit(&allocq->vpmq_mtx);
                        mutex_exit(&releq->vpmq_mtx);
                        if (page_locked) {
                                ddi_msleep(250);
                                page_locked = 0;
                        }
                        goto retry_queue;
                }
        } else {
                int gotnewvpm;
                kmutex_t *pmtx;
                uint_t vpmref;

                /*
                 * Fastpath the case we get the vpmap mutex
                 * on the first try.
                 */
                first = vpm;
next_vpmap:
                vmtx = VPMAPMTX(vpm);
                if (!mutex_tryenter(vmtx)) {
                        /*
                         * Another thread is trying to reclaim this slot.
                         * Skip to the next queue or vpmap.
                         */
                        if ((vpm = vpm->vpm_next) == first) {
                                goto skip_queue;
                        } else {
                                goto next_vpmap;
                        }
                }

                /*
                 * Assign this vpm to the newpage.
                 */
                pmtx = PPMTX(newpage);
                gotnewvpm = 0;
                mutex_enter(pmtx);

                /*
                 * Check if some other thread already assigned a vpm to
                 * this page.
                 */
                if ((vpmref = newpage->p_vpmref) == 0) {
                        newpage->p_vpmref = VPMID(vpm);
                        gotnewvpm = 1;
                } else {
                        VPM_DEBUG(vpmd_contend);
                        mutex_exit(vmtx);
                }
                mutex_exit(pmtx);

                if (gotnewvpm) {

                        /*
                         * At this point, we've selected the vpm. Remove vpm
                         * from its freelist. If vpm is the first one in
                         * the freelist, update the head of the freelist.
                         */
                        if (first == vpm) {
                                ASSERT(first == allocq->vpmq_free);
                                allocq->vpmq_free = vpm->vpm_next;
                        }

                        /*
                         * If the head of the freelist still points to vpm,
                         * then there are no more free vpmaps in that list.
                         */
                        if (allocq->vpmq_free == vpm)
                                /*
                                 * Took the last one
                                 */
                                allocq->vpmq_free = NULL;
                        else {
                                vpm->vpm_prev->vpm_next = vpm->vpm_next;
                                vpm->vpm_next->vpm_prev = vpm->vpm_prev;
                        }
                        mutex_exit(&allocq->vpmq_mtx);
                        vpm->vpm_prev = vpm->vpm_next = NULL;

                        /*
                         * Disassociate the previous page.
                         * p_vpmref is used as a mapping reference to the page.
                         */
                        if ((pp = vpm->vpm_pp) != NULL &&
                            vpm->vpm_vp == pp->p_vnode &&
                            vpm->vpm_off == pp->p_offset) {

                                pmtx = PPMTX(pp);
                                if (page_trylock(pp, SE_SHARED)) {
                                        /*
                                         * Now verify that it is the correct
                                         * page. If not someone else stole it,
                                         * so just unlock it and leave.
                                         */
                                        mutex_enter(pmtx);
                                        if (PP_ISFREE(pp) ||
                                            vpm->vpm_vp != pp->p_vnode ||
                                            vpm->vpm_off != pp->p_offset ||
                                            pp->p_vpmref != VPMID(vpm)) {
                                                mutex_exit(pmtx);

                                                page_unlock(pp);
                                        } else {
                                                /*
                                                 * Release the page.
                                                 */
                                                pp->p_vpmref = 0;
                                                mutex_exit(pmtx);
                                                (void) page_release(pp, 1);
                                        }
                                } else {
                                        /*
                                         * If the page cannot be locked, just
                                         * clear the p_vpmref and go.
                                         */
                                        mutex_enter(pmtx);
                                        if (pp->p_vpmref == VPMID(vpm)) {
                                                pp->p_vpmref = 0;
                                        }
                                        mutex_exit(pmtx);
                                        VPM_DEBUG(vpmd_prevpagelocked);
                                }
                        }

                        /*
                         * Setup vpm to point to the new page.
                         */
                        vpm->vpm_pp = newpage;
                        vpm->vpm_vp = newpage->p_vnode;
                        vpm->vpm_off = newpage->p_offset;

                } else {
                        int steal = !VPM_MTBF(steals, steals_mtbf);
                        /*
                         * Page already has a vpm assigned just use that.
                         * Grab the vpm mutex and verify that it is still
                         * the correct one. The pp->p_vpmref should not change
                         * once we have the vpm mutex and the page lock.
                         */
                        mutex_exit(&allocq->vpmq_mtx);
                        vpm = VPMP(vpmref);
                        vmtx = VPMAPMTX(vpm);
                        mutex_enter(vmtx);
                        if ((steal && vpm->vpm_refcnt == 0) ||
                            vpm->vpm_pp != newpage) {
                                /*
                                 * The vpm got stolen, retry.
                                 * clear the p_vpmref.
                                 */
                                pmtx = PPMTX(newpage);
                                mutex_enter(pmtx);
                                if (newpage->p_vpmref == vpmref) {
                                        newpage->p_vpmref = 0;
                                }
                                mutex_exit(pmtx);

                                mutex_exit(vmtx);
                                VPM_DEBUG(vpmd_steals);
                                goto retry_queue;
                        } else if (vpm->vpm_refcnt == 0) {
                                /*
                                 * Remove it from the free list if it
                                 * exists there.
                                 */
                                VPMAP_RMFREELIST(vpm);
                        }
                }
                return (vpm);
        }
}

static void
free_vpmap(struct vpmap *vpm)
{
        struct vpmfree *vpmflp;
        struct vpmap *vpmfreelist;
        union vpm_freeq *releq;

        ASSERT(MUTEX_HELD(VPMAPMTX(vpm)));

        if (vpm->vpm_refcnt != 0) {
                panic("free_vpmap");
                /*NOTREACHED*/
        }

        vpmflp = &vpmd_free[vpm->vpm_free_ndx];
        /*
         * Add to the tail of the release queue
         * Note that vpm_releq and vpm_allocq could toggle
         * before we get the lock. This does not affect
         * correctness as the 2 queues are only maintained
         * to reduce lock pressure.
         */
        releq = vpmflp->vpm_releq;
        if (releq == &vpmflp->vpm_freeq[0]) {
                vpm->vpm_ndxflg = 0;
        } else {
                vpm->vpm_ndxflg = 1;
        }
        mutex_enter(&releq->vpmq_mtx);
        vpmfreelist = releq->vpmq_free;
        if (vpmfreelist == 0) {
                int want;

                releq->vpmq_free = vpm->vpm_next = vpm->vpm_prev = vpm;
                /*
                 * Both queue mutexes are held to set vpm_want;
                 * snapshot the value before dropping releq mutex.
                 * If vpm_want appears after the releq mutex is dropped,
                 * then the vpmap just freed is already gone.
                 */
                want = vpmflp->vpm_want;
                mutex_exit(&releq->vpmq_mtx);
                /*
                 * See if there was a waiter before dropping the releq mutex
                 * then recheck after obtaining vpm_freeq[0] mutex as
                 * the another thread may have already signaled.
                 */
                if (want) {
                        mutex_enter(&vpmflp->vpm_freeq[0].vpmq_mtx);
                        if (vpmflp->vpm_want)
                                cv_signal(&vpmflp->vpm_free_cv);
                        mutex_exit(&vpmflp->vpm_freeq[0].vpmq_mtx);
                }
        } else {
                vpm->vpm_next = vpmfreelist;
                vpm->vpm_prev = vpmfreelist->vpm_prev;
                vpmfreelist->vpm_prev = vpm;
                vpm->vpm_prev->vpm_next = vpm;
                mutex_exit(&releq->vpmq_mtx);
        }
}

/*
 * Get the vpmap for the page.
 * The refcnt of this vpm is incremented.
 */
static struct vpmap *
get_vpmap(page_t *pp)
{
        struct vpmap *vpm = NULL;
        kmutex_t *vmtx;
        kmutex_t *pmtx;
        unsigned int refid;

        ASSERT((pp != NULL) && PAGE_LOCKED(pp));

        if (VPM_MTBF(contend, contend_mtbf) && (refid = pp->p_vpmref) != 0) {
                vpm = VPMP(refid);
                vmtx = VPMAPMTX(vpm);
                mutex_enter(vmtx);
                /*
                 * Since we have the page lock and the vpm mutex, the
                 * pp->p_vpmref cannot change.
                 */
                if (vpm->vpm_pp != pp) {
                        pmtx = PPMTX(pp);

                        /*
                         * Clear the p_vpmref as it is incorrect.
                         * This can happen if the page was stolen.
                         * On x64 this should not happen as p_vpmref
                         * is treated as a mapping on the page. So
                         * if the page is stolen, the mapping would have
                         * been cleared in page_unload().
                         */
                        mutex_enter(pmtx);
                        if (pp->p_vpmref == refid)
                                pp->p_vpmref = 0;
                        mutex_exit(pmtx);

                        mutex_exit(vmtx);
                        vpm = NULL;
                } else if (vpm->vpm_refcnt == 0) {
                        /*
                         * Got the vpm, remove it from the free
                         * list if it exists there.
                         */
                        VPMAP_RMFREELIST(vpm);
                }
        }
        if (vpm == NULL) {
                /*
                 * get_free_vpmap() returns with the vpmap mutex held.
                 */
                vpm = get_free_vpmap(pp);
                vmtx = VPMAPMTX(vpm);
                vpmd_cpu[CPU->cpu_seqid].vcpu.vcpu_misses++;
        } else {
                vpmd_cpu[CPU->cpu_seqid].vcpu.vcpu_hits++;
        }

        vpm->vpm_refcnt++;
        mutex_exit(vmtx);

        return (vpm);
}

/* END --- vpm cache ---- */

/*
 * The vnode page mapping(vpm) interface routines.
 */

/*
 * Find or create the pages starting form baseoff for specified
 * length 'len'.
 */
static int
vpm_pagecreate(
        struct vnode *vp,
        uoff_t baseoff,
        size_t len,
        vmap_t vml[],
        int nseg,
        int *newpage)
{

        page_t *pp = NULL;
        caddr_t base;
        uoff_t off = baseoff;
        int i;
        ASSERT(nseg >= MINVMAPS && nseg <= MAXVMAPS);

        for (i = 0; len > 0; len -= PAGESIZE, i++) {
                struct vpmap *vpm;


                if ((pp = page_lookup(&vp->v_object, off, SE_SHARED)) == NULL) {

                        base = segkpm_create_va(off);

                        /*
                         * the seg pointer passed in is just advisor. Just
                         * pass segkmap for now like segmap does with
                         * segmap_kpm enabled.
                         */
                        if ((pp = page_create_va(&vp->v_object, off, PAGESIZE,
                                                 PG_WAIT, segkmap,
                                                 base)) == NULL) {
                                panic("segmap_pagecreate_vpm: "
                                    "page_create failed");
                                /*NOTREACHED*/
                        }
                        if (newpage != NULL)
                                *newpage = 1;

                        page_io_unlock(pp);
                }

                /*
                 * Get the vpm for this page_t.
                 */
                if (vpm_cache_enable) {
                        vpm = get_vpmap(pp);
                        vml[i].vs_data = (void *)&vpm->vpm_pp;
                } else {
                        vml[i].vs_data = (void *)pp;
                        pp->p_vpmref = 0;
                }

                vml[i].vs_addr = hat_kpm_mapin(pp, 0);
                vml[i].vs_len = PAGESIZE;

                off += PAGESIZE;
        }
        vml[i].vs_data = NULL;
        vml[i].vs_addr = NULL;
        return (0);
}


/*
 * Returns vpm mappings of pages in the range [off, off+len], where
 * len is rounded up to the PAGESIZE boundary. The list of pages and
 * the page addresses are returned in the SGL vml (vmap_t) array passed in.
 * The nseg is the number of vmap_t entries in the array.
 *
 * The segmap's SM_LOCKPROTO  usage is not supported by these interfaces.
 * For such cases, use the seg_map interfaces.
 */
int
vpm_map_pages(
        struct vnode *vp,
        uoff_t off,
        size_t len,
        int fetchpage,
        vmap_t *vml,
        int nseg,
        int  *newpage,
        enum seg_rw rw)
{
        extern struct vnode *common_specvp();
        uoff_t baseoff;
        uint_t prot;
        caddr_t base;
        page_t *pp, *pplist[MAXVMAPS];
        struct vpmap *vpm;
        int i, error = 0;
        size_t tlen;

        ASSERT(nseg >= MINVMAPS && nseg <= MAXVMAPS);
        baseoff = off & (offset_t)PAGEMASK;
        vml[0].vs_data = NULL;
        vml[0].vs_addr = NULL;

        tlen = P2ROUNDUP(off + len, PAGESIZE) - baseoff;
        /*
         * Restrict it to VPMMAXLEN.
         */
        if (tlen > (VPMMAXPGS * PAGESIZE)) {
                tlen = VPMMAXPGS * PAGESIZE;
        }
        /*
         * Ensure length fits within the vml[] array. One element of
         * the array is used to mark the end of the scatter/gather list
         * of valid mappings by setting its vs_addr = NULL. Leave space
         * for this element.
         */
        if (tlen > ((nseg - 1) * PAGESIZE)) {
                tlen = ((nseg - 1) * PAGESIZE);
        }
        len = tlen;

        /*
         * If this is a block device we have to be sure to use the
         * "common" block device vnode for the mapping.
         */
        if (vp->v_type == VBLK)
                vp = common_specvp(vp);


        if (!fetchpage)
                return (vpm_pagecreate(vp, baseoff, len, vml, nseg, newpage));

        for (i = 0; len > 0; len -= PAGESIZE, i++, pplist[i] = NULL) {

                pp = page_lookup(&vp->v_object, baseoff, SE_SHARED);

                /*
                 * If we did not find the page or if this page was not
                 * in vpm cache(p_vpmref == 0), then let fop_getpage get
                 * all the pages.
                 * We need to call fop_getpage so that filesystems can do some
                 * (un)necessary tracking for sequential access.
                 */

                if (pp == NULL || (vpm_cache_enable && pp->p_vpmref == 0) ||
                    (rw == S_WRITE && hat_page_getattr(pp, P_MOD | P_REF)
                    != (P_MOD | P_REF))) {
                        int j;
                        if (pp != NULL) {
                                page_unlock(pp);
                        }
                        /*
                         * If we did not find the desired set of pages,
                         * from the page cache, just call fop_getpage to get
                         * all the pages.
                         */
                        for (j = 0; j < i; j++) {
                                page_unlock(pplist[j]);
                        }


                        baseoff = off & (offset_t)PAGEMASK;
                        /*
                         * Pass a dummy address as it will be required
                         * by page_create_va(). We pass segkmap as the seg
                         * as some file systems(UFS) check it.
                         */
                        base = segkpm_create_va(baseoff);

                        error = fop_getpage(vp, baseoff, tlen, &prot, pplist,
                            tlen, segkmap, base, rw, CRED(), NULL);
                        if (error) {
                                VPM_DEBUG(vpmd_getpagefailed);
                                pplist[0] = NULL;
                        }
                        break;
                } else {
                        pplist[i] = pp;
                        baseoff += PAGESIZE;
                }
        }

        if (error) {
                for (i = 0; pplist[i] != NULL; i++) {
                        page_unlock(pplist[i]);
                        pplist[i] = NULL;
                }
                vml[0].vs_addr = NULL;
                vml[0].vs_data = NULL;
                return (error);
        }

        /*
         * Get the vpm's for pages.
         */
        for (i = 0; pplist[i] != NULL; i++) {
                if (vpm_cache_enable) {
                        vpm = get_vpmap(pplist[i]);
                        vml[i].vs_data = (void *)&(vpm->vpm_pp);
                } else {
                        vml[i].vs_data = (void *)pplist[i];
                        pplist[i]->p_vpmref = 0;
                }

                vml[i].vs_addr = hat_kpm_mapin(pplist[i], 0);
                vml[i].vs_len = PAGESIZE;
        }

        vml[i].vs_data = NULL;
        vml[i].vs_addr = NULL;

        return (0);
}

/*
 * Release the vpm mappings on the pages and unlock them.
 */
void
vpm_unmap_pages(vmap_t vml[], enum seg_rw rw)
{
        int i;
        struct vpmap *vpm;
        kmutex_t *mtx;
        page_t *pp;

        for (i = 0; vml[i].vs_data != NULL; i++) {
                ASSERT(IS_KPM_ADDR(vml[i].vs_addr));

                if (vpm_cache_enable) {
                        pp = *(((page_t **)vml[i].vs_data));
                } else {
                        pp = (page_t *)vml[i].vs_data;
                }

                /*
                 * Mark page as being modified or referenced, bacause vpm pages
                 * would not cause faults where it would be set normally.
                 */
                if (rw == S_WRITE) {
                        hat_setrefmod(pp);
                } else {
                        ASSERT(rw == S_READ);
                        hat_setref(pp);
                }

                if (vpm_cache_enable) {
                        vpm = (struct vpmap *)((char *)vml[i].vs_data
                            - offsetof(struct vpmap, vpm_pp));
                        hat_kpm_mapout(pp, 0, vml[i].vs_addr);
                        page_unlock(pp);
                        mtx = VPMAPMTX(vpm);
                        mutex_enter(mtx);

                        if (--vpm->vpm_refcnt == 0) {
                                free_vpmap(vpm);
                        }
                        mutex_exit(mtx);
                } else {
                        hat_kpm_mapout(pp, 0, vml[i].vs_addr);
                        (void) page_release(pp, 1);
                }
                vml[i].vs_data = NULL;
                vml[i].vs_addr = NULL;
        }
}

/*
 * Given the vp, off and the uio structure, this routine will do the
 * the copy (uiomove). If the last page created is partially written,
 * the rest of the page is zeroed out. It also zeros the beginning of
 * the first page till the start offset if requested(zerostart).
 * If pages are to be fetched, it will call the filesystem's getpage
 * function (fop_getpage) to get them, otherwise they will be created if
 * not already present in the page cache.
 */
int
vpm_data_copy(struct vnode *vp,
        uoff_t off,
        size_t len,
        struct uio *uio,
        int fetchpage,
        int *newpage,
        int zerostart,
        enum seg_rw rw)
{
        int error;
        struct vmap vml[MINVMAPS];
        enum uio_rw uiorw;
        int npages = 0;

        uiorw = (rw == S_WRITE) ? UIO_WRITE : UIO_READ;
        /*
         * 'off' will be the offset where the I/O starts.
         * We get the pages starting at the (off & PAGEMASK)
         * page boundary.
         */
        error = vpm_map_pages(vp, off, (uint_t)len,
            fetchpage, vml, MINVMAPS, &npages,  rw);

        if (newpage != NULL)
                *newpage = npages;
        if (!error) {
                int i, pn, slen = len;
                int pon = off & PAGEOFFSET;

                /*
                 * Clear from the beginning of the page to start offset
                 * if requested.
                 */
                if (!fetchpage && zerostart) {
                        (void) kzero(vml[0].vs_addr,  (uint_t)pon);
                        VPM_DEBUG(vpmd_zerostart);
                }

                for (i = 0; !error && slen > 0 &&
                    vml[i].vs_addr != NULL; i++) {
                        pn = (int)MIN(slen, (PAGESIZE - pon));
                        error = uiomove(vml[i].vs_addr + pon,
                            (long)pn, uiorw, uio);
                        slen -= pn;
                        pon = 0;
                }

                /*
                 * When new pages are created, zero out part of the
                 * page we did not copy to.
                 */
                if (!fetchpage && npages &&
                    uio->uio_loffset < roundup(off + len, PAGESIZE)) {
                        int nzero;

                        pon = (uio->uio_loffset & PAGEOFFSET);
                        nzero = PAGESIZE  - pon;
                        i = (uio->uio_loffset - (off & PAGEMASK)) / PAGESIZE;
                        (void) kzero(vml[i].vs_addr + pon, (uint_t)nzero);
                }
                vpm_unmap_pages(vml, rw);
        }
        return (error);
}

/*
 * called to flush pages for the given vnode covering
 * [off, off+len] range.
 */
int
vpm_sync_pages(struct vnode *vp,
                uoff_t off,
                size_t len,
                uint_t flags)
{
        extern struct vnode *common_specvp();
        int bflags = 0;
        int error = 0;
        size_t psize = roundup(len, PAGESIZE);

        /*
         * If this is a block device we have to be sure to use the
         * "common" block device vnode for the mapping.
         */
        if (vp->v_type == VBLK)
                vp = common_specvp(vp);

        if ((flags & ~SM_DONTNEED) != 0) {
                if (flags & SM_ASYNC)
                        bflags |= B_ASYNC;
                if (flags & SM_INVAL)
                        bflags |= B_INVAL;
                if (flags & SM_DESTROY)
                        bflags |= (B_INVAL|B_TRUNC);
                if (flags & SM_FREE)
                        bflags |= B_FREE;
                if (flags & SM_DONTNEED)
                        bflags |= B_DONTNEED;

                error = fop_putpage(vp, off, psize, bflags, CRED(), NULL);
        }

        return (error);
}


#else   /* SEGKPM_SUPPORT */

/* vpm stubs */
void
vpm_init()
{
}

/*ARGSUSED*/
int
vpm_pagecreate(
        struct vnode *vp,
        uoff_t baseoff,
        size_t len,
        vmap_t vml[],
        int nseg,
        int *newpage)
{
        return (0);
}

/*ARGSUSED*/
int
vpm_map_pages(
        struct vnode *vp,
        uoff_t off,
        size_t len,
        int fetchpage,
        vmap_t vml[],
        int nseg,
        int *newpage,
        enum seg_rw rw)
{
        return (0);
}

/*ARGSUSED*/
int
vpm_data_copy(struct vnode *vp,
        uoff_t off,
        size_t len,
        struct uio *uio,
        int fetchpage,
        int *newpage,
        int zerostart,
        enum seg_rw rw)
{
        return (0);
}

/*ARGSUSED*/
void
vpm_unmap_pages(vmap_t vml[], enum seg_rw rw)
{
}
/*ARGSUSED*/
int
vpm_sync_pages(struct vnode *vp,
                uoff_t off,
                size_t len,
                uint_t flags)
{
        return (0);
}
#endif  /* SEGKPM_SUPPORT */