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md: Get rid of the pbuf zone

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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
This commit is contained in:
Mark Johnston 2023-05-23 10:14:06 -04:00
parent 21a16d55cc
commit 30038a8b4e
1 changed files with 16 additions and 16 deletions
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32
sys/dev/md/md.c
View file

@ -98,6 +98,7 @@
#include <geom/geom_int.h>
#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/vm_param.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
@ -232,8 +233,6 @@ static LIST_HEAD(, md_s) md_softc_list = LIST_HEAD_INITIALIZER(md_softc_list);
#define NMASK (NINDIR-1)
static int nshift;
static uma_zone_t md_pbuf_zone;
struct indir {
uintptr_t *array;
u_int total;
@ -276,6 +275,7 @@ struct md_s {
char file[PATH_MAX];
char label[PATH_MAX];
struct ucred *cred;
vm_offset_t kva;
/* MD_SWAP related fields */
vm_object_t object;
@ -877,11 +877,11 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
struct iovec *piov;
struct mount *mp;
struct vnode *vp;
struct buf *pb;
bus_dma_segment_t *vlist;
struct thread *td;
off_t iolen, iostart, off, len;
int ma_offs, npages;
bool mapped;
switch (bp->bio_cmd) {
case BIO_READ:
@ -902,11 +902,11 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
td = curthread;
vp = sc->vnode;
pb = NULL;
piov = NULL;
ma_offs = bp->bio_ma_offset;
off = bp->bio_offset;
len = bp->bio_length;
mapped = false;
/*
* VNODE I/O
@ -955,22 +955,21 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
auio.uio_iovcnt = piov - auio.uio_iov;
piov = auio.uio_iov;
} else if ((bp->bio_flags & BIO_UNMAPPED) != 0) {
pb = uma_zalloc(md_pbuf_zone, M_WAITOK);
MPASS((pb->b_flags & B_MAXPHYS) != 0);
bp->bio_resid = len;
unmapped_step:
npages = atop(min(maxphys, round_page(len + (ma_offs &
PAGE_MASK))));
iolen = min(ptoa(npages) - (ma_offs & PAGE_MASK), len);
KASSERT(iolen > 0, ("zero iolen"));
pmap_qenter((vm_offset_t)pb->b_data,
&bp->bio_ma[atop(ma_offs)], npages);
aiov.iov_base = (void *)((vm_offset_t)pb->b_data +
(ma_offs & PAGE_MASK));
KASSERT(npages <= atop(MAXPHYS + PAGE_SIZE),
("npages %d too large", npages));
pmap_qenter(sc->kva, &bp->bio_ma[atop(ma_offs)], npages);
aiov.iov_base = (void *)(sc->kva + (ma_offs & PAGE_MASK));
aiov.iov_len = iolen;
auio.uio_iov = &aiov;
auio.uio_iovcnt = 1;
auio.uio_resid = iolen;
mapped = true;
} else {
aiov.iov_base = bp->bio_data;
aiov.iov_len = bp->bio_length;
@ -998,8 +997,8 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
VOP_ADVISE(vp, iostart, auio.uio_offset - 1,
POSIX_FADV_DONTNEED);
if (pb != NULL) {
pmap_qremove((vm_offset_t)pb->b_data, npages);
if (mapped) {
pmap_qremove(sc->kva, npages);
if (error == 0) {
len -= iolen;
bp->bio_resid -= iolen;
@ -1007,7 +1006,6 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
if (len > 0)
goto unmapped_step;
}
uma_zfree(md_pbuf_zone, pb);
} else {
bp->bio_resid = auio.uio_resid;
}
@ -1276,7 +1274,7 @@ mdnew(int unit, int *errp, enum md_types type)
return (NULL);
}
sc = (struct md_s *)malloc(sizeof *sc, M_MD, M_WAITOK | M_ZERO);
sc = malloc(sizeof(*sc), M_MD, M_WAITOK | M_ZERO);
sc->type = type;
bioq_init(&sc->bio_queue);
mtx_init(&sc->queue_mtx, "md bio queue", NULL, MTX_DEF);
@ -1484,6 +1482,8 @@ mdcreate_vnode(struct md_s *sc, struct md_req *mdr, struct thread *td)
nd.ni_vp->v_vflag &= ~VV_MD;
goto bad;
}
sc->kva = kva_alloc(MAXPHYS + PAGE_SIZE);
return (0);
bad:
VOP_UNLOCK(nd.ni_vp);
@ -1542,6 +1542,8 @@ mddestroy(struct md_s *sc, struct thread *td)
destroy_indir(sc, sc->indir);
if (sc->uma)
uma_zdestroy(sc->uma);
if (sc->kva)
kva_free(sc->kva, MAXPHYS + PAGE_SIZE);
LIST_REMOVE(sc, list);
free_unr(md_uh, sc->unit);
@ -2076,7 +2078,6 @@ g_md_init(struct g_class *mp __unused)
sx_xunlock(&md_sx);
}
}
md_pbuf_zone = pbuf_zsecond_create("mdpbuf", nswbuf / 10);
status_dev = make_dev(&mdctl_cdevsw, INT_MAX, UID_ROOT, GID_WHEEL,
0600, MDCTL_NAME);
g_topology_lock();
@ -2172,6 +2173,5 @@ g_md_fini(struct g_class *mp __unused)
sx_destroy(&md_sx);
if (status_dev != NULL)
destroy_dev(status_dev);
uma_zdestroy(md_pbuf_zone);
delete_unrhdr(md_uh);
}