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Usa a globally visible region of zeros for both /dev/zero and the md

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device.  There are likely other kernel uses of "blob of zeros" than can
be converted.

Reviewed by:	alc
MFC after:	1 week
This commit is contained in:
Matthew D Fleming 2011-05-13 18:48:00 +00:00
parent 14f9771b27
commit 89cb2a19ec
4 changed files with 51 additions and 11 deletions
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8
sys/dev/md/md.c
View File

@ -205,9 +205,6 @@ struct md_s {
vm_object_t object;
};
/* Used for BIO_DELETE on MD_VNODE */
static u_char zero[PAGE_SIZE];
static struct indir *
new_indir(u_int shift)
{
@ -560,7 +557,8 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
* that the two cases end up having very little in common.
*/
if (bp->bio_cmd == BIO_DELETE) {
zerosize = sizeof(zero) - (sizeof(zero) % sc->sectorsize);
zerosize = ZERO_REGION_SIZE -
(ZERO_REGION_SIZE % sc->sectorsize);
auio.uio_iov = &aiov;
auio.uio_iovcnt = 1;
auio.uio_offset = (vm_ooffset_t)bp->bio_offset;
@ -573,7 +571,7 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
error = 0;
while (auio.uio_offset < end) {
aiov.iov_base = zero;
aiov.iov_base = __DECONST(void *, zero_region);
aiov.iov_len = end - auio.uio_offset;
if (aiov.iov_len > zerosize)
aiov.iov_len = zerosize;

17
sys/dev/null/null.c
View File

@ -65,8 +65,6 @@ static struct cdevsw zero_cdevsw = {
.d_flags = D_MMAP_ANON,
};
static void *zbuf;
/* ARGSUSED */
static int
null_write(struct cdev *dev __unused, struct uio *uio, int flags __unused)
@ -95,10 +93,19 @@ null_ioctl(struct cdev *dev __unused, u_long cmd, caddr_t data __unused,
static int
zero_read(struct cdev *dev __unused, struct uio *uio, int flags __unused)
{
void *zbuf;
ssize_t len;
int error = 0;
while (uio->uio_resid > 0 && error == 0)
error = uiomove(zbuf, MIN(uio->uio_resid, PAGE_SIZE), uio);
KASSERT(uio->uio_rw == UIO_READ,
("Can't be in %s for write", __func__));
zbuf = __DECONST(void *, zero_region);
while (uio->uio_resid > 0 && error == 0) {
len = uio->uio_resid;
if (len > ZERO_REGION_SIZE)
len = ZERO_REGION_SIZE;
error = uiomove(zbuf, len, uio);
}
return (error);
}
@ -111,7 +118,6 @@ null_modevent(module_t mod __unused, int type, void *data __unused)
case MOD_LOAD:
if (bootverbose)
printf("null: <null device, zero device>\n");
zbuf = (void *)malloc(PAGE_SIZE, M_TEMP, M_WAITOK | M_ZERO);
null_dev = make_dev_credf(MAKEDEV_ETERNAL_KLD, &null_cdevsw, 0,
NULL, UID_ROOT, GID_WHEEL, 0666, "null");
zero_dev = make_dev_credf(MAKEDEV_ETERNAL_KLD, &zero_cdevsw, 0,
@ -121,7 +127,6 @@ null_modevent(module_t mod __unused, int type, void *data __unused)
case MOD_UNLOAD:
destroy_dev(null_dev);
destroy_dev(zero_dev);
free(zbuf, M_TEMP);
break;
case MOD_SHUTDOWN:

3
sys/sys/systm.h
View File

@ -125,6 +125,9 @@ extern char static_hints[]; /* by config for now */
extern char **kenvp;
extern const void *zero_region; /* address space maps to a zeroed page */
#define ZERO_REGION_SIZE (2048 * 1024)
/*
* General function declarations.
*/

34
sys/vm/vm_kern.c
View File

@ -91,6 +91,9 @@ vm_map_t exec_map=0;
vm_map_t pipe_map;
vm_map_t buffer_map=0;
const void *zero_region;
CTASSERT((ZERO_REGION_SIZE & PAGE_MASK) == 0);
/*
* kmem_alloc_nofault:
*
@ -527,6 +530,35 @@ kmem_free_wakeup(map, addr, size)
vm_map_unlock(map);
}
static void
kmem_init_zero_region(void)
{
vm_offset_t addr;
vm_page_t m;
unsigned int i;
int error;
/* Allocate virtual address space. */
addr = kmem_alloc_nofault(kernel_map, ZERO_REGION_SIZE);
/* Allocate a page and zero it. */
m = vm_page_alloc(NULL, OFF_TO_IDX(addr - VM_MIN_KERNEL_ADDRESS),
VM_ALLOC_NOOBJ | VM_ALLOC_WIRED | VM_ALLOC_ZERO);
if ((m->flags & PG_ZERO) == 0)
pmap_zero_page(m);
/* Map the address space to the page. */
for (i = 0; i < ZERO_REGION_SIZE; i += PAGE_SIZE)
pmap_qenter(addr + i, &m, 1);
/* Protect it r/o. */
error = vm_map_protect(kernel_map, addr, addr + ZERO_REGION_SIZE,
VM_PROT_READ, TRUE);
KASSERT(error == 0, ("error=%d", error));
zero_region = (const void *)addr;
}
/*
* kmem_init:
*
@ -555,6 +587,8 @@ kmem_init(start, end)
start, VM_PROT_ALL, VM_PROT_ALL, MAP_NOFAULT);
/* ... and ending with the completion of the above `insert' */
vm_map_unlock(m);
kmem_init_zero_region();
}
#ifdef DIAGNOSTIC