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md: Get rid of the pbuf zone
The zone is used solely to provide KVA for mapping BIOs so that we can pass mapped buffers to VOP_READ and VOP_WRITE. Currently we preallocate nswbuf/10 bufs for this purpose during boot. The intent was to limit KVA usage on 32-bit systems, but the preallocation means that we in fact consumed more KVA than needed unless one has more than nswbuf/10 (typically 25) vnode-backed MD devices in existence, which I would argue is the uncommon case. Meanwhile, all I/O to an MD is handled by a dedicated thread, so we can instead simply preallocate the KVA region at MD device creation time. Event: BSDCan 2023 Reviewed by: kib MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D40215
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@ -98,6 +98,7 @@
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#include <geom/geom_int.h>
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#include <vm/vm.h>
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#include <vm/vm_extern.h>
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#include <vm/vm_param.h>
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#include <vm/vm_object.h>
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#include <vm/vm_page.h>
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@ -232,8 +233,6 @@ static LIST_HEAD(, md_s) md_softc_list = LIST_HEAD_INITIALIZER(md_softc_list);
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#define NMASK (NINDIR-1)
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static int nshift;
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static uma_zone_t md_pbuf_zone;
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struct indir {
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uintptr_t *array;
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u_int total;
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@ -276,6 +275,7 @@ struct md_s {
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char file[PATH_MAX];
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char label[PATH_MAX];
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struct ucred *cred;
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vm_offset_t kva;
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/* MD_SWAP related fields */
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vm_object_t object;
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@ -877,11 +877,11 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
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struct iovec *piov;
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struct mount *mp;
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struct vnode *vp;
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struct buf *pb;
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bus_dma_segment_t *vlist;
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struct thread *td;
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off_t iolen, iostart, off, len;
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int ma_offs, npages;
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bool mapped;
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switch (bp->bio_cmd) {
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case BIO_READ:
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@ -902,11 +902,11 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
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td = curthread;
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vp = sc->vnode;
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pb = NULL;
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piov = NULL;
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ma_offs = bp->bio_ma_offset;
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off = bp->bio_offset;
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len = bp->bio_length;
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mapped = false;
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/*
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* VNODE I/O
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@ -955,22 +955,21 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
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auio.uio_iovcnt = piov - auio.uio_iov;
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piov = auio.uio_iov;
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} else if ((bp->bio_flags & BIO_UNMAPPED) != 0) {
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pb = uma_zalloc(md_pbuf_zone, M_WAITOK);
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MPASS((pb->b_flags & B_MAXPHYS) != 0);
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bp->bio_resid = len;
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unmapped_step:
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npages = atop(min(maxphys, round_page(len + (ma_offs &
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PAGE_MASK))));
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iolen = min(ptoa(npages) - (ma_offs & PAGE_MASK), len);
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KASSERT(iolen > 0, ("zero iolen"));
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pmap_qenter((vm_offset_t)pb->b_data,
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&bp->bio_ma[atop(ma_offs)], npages);
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aiov.iov_base = (void *)((vm_offset_t)pb->b_data +
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(ma_offs & PAGE_MASK));
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KASSERT(npages <= atop(MAXPHYS + PAGE_SIZE),
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("npages %d too large", npages));
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pmap_qenter(sc->kva, &bp->bio_ma[atop(ma_offs)], npages);
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aiov.iov_base = (void *)(sc->kva + (ma_offs & PAGE_MASK));
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aiov.iov_len = iolen;
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auio.uio_iov = &aiov;
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auio.uio_iovcnt = 1;
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auio.uio_resid = iolen;
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mapped = true;
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} else {
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aiov.iov_base = bp->bio_data;
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aiov.iov_len = bp->bio_length;
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@ -998,8 +997,8 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
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VOP_ADVISE(vp, iostart, auio.uio_offset - 1,
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POSIX_FADV_DONTNEED);
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if (pb != NULL) {
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pmap_qremove((vm_offset_t)pb->b_data, npages);
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if (mapped) {
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pmap_qremove(sc->kva, npages);
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if (error == 0) {
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len -= iolen;
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bp->bio_resid -= iolen;
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@ -1007,7 +1006,6 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
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if (len > 0)
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goto unmapped_step;
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}
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uma_zfree(md_pbuf_zone, pb);
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} else {
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bp->bio_resid = auio.uio_resid;
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}
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@ -1276,7 +1274,7 @@ mdnew(int unit, int *errp, enum md_types type)
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return (NULL);
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}
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sc = (struct md_s *)malloc(sizeof *sc, M_MD, M_WAITOK | M_ZERO);
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sc = malloc(sizeof(*sc), M_MD, M_WAITOK | M_ZERO);
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sc->type = type;
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bioq_init(&sc->bio_queue);
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mtx_init(&sc->queue_mtx, "md bio queue", NULL, MTX_DEF);
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@ -1484,6 +1482,8 @@ mdcreate_vnode(struct md_s *sc, struct md_req *mdr, struct thread *td)
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nd.ni_vp->v_vflag &= ~VV_MD;
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goto bad;
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}
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sc->kva = kva_alloc(MAXPHYS + PAGE_SIZE);
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return (0);
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bad:
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VOP_UNLOCK(nd.ni_vp);
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@ -1542,6 +1542,8 @@ mddestroy(struct md_s *sc, struct thread *td)
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destroy_indir(sc, sc->indir);
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if (sc->uma)
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uma_zdestroy(sc->uma);
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if (sc->kva)
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kva_free(sc->kva, MAXPHYS + PAGE_SIZE);
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LIST_REMOVE(sc, list);
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free_unr(md_uh, sc->unit);
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@ -2076,7 +2078,6 @@ g_md_init(struct g_class *mp __unused)
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sx_xunlock(&md_sx);
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}
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}
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md_pbuf_zone = pbuf_zsecond_create("mdpbuf", nswbuf / 10);
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status_dev = make_dev(&mdctl_cdevsw, INT_MAX, UID_ROOT, GID_WHEEL,
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0600, MDCTL_NAME);
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g_topology_lock();
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@ -2172,6 +2173,5 @@ g_md_fini(struct g_class *mp __unused)
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sx_destroy(&md_sx);
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if (status_dev != NULL)
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destroy_dev(status_dev);
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uma_zdestroy(md_pbuf_zone);
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delete_unrhdr(md_uh);
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}
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