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Speed up geom_stats_resync in the presence of many devices

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The old code had a O(n) loop, where n is the size of /dev/devstat.
Multiply that by another O(n) loop in devstat_mmap for a total of
O(n^2).

This change adds DIOCGMEDIASIZE support to /dev/devstat so userland can
quickly determine the right amount of memory to map, eliminating the
O(n) loop in userland.

This change decreases the time to run "gstat -bI0.001" with 16,384 md
devices from 29.7s to 4.2s.

Also, fix a memory leak first reported as PR 203097.

Sponsored by:	Axcient
Reviewed by:	mav, imp
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D28968
This commit is contained in:
Alan Somers 2021-02-27 08:59:40 -07:00
parent afb1aa4e6d
commit ab63da3564
2 changed files with 38 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
lib/libgeom/geom_stats.c
View File

@ -32,9 +32,12 @@
*/
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/disk.h>
#include <sys/devicestat.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
@ -53,7 +56,7 @@ geom_stats_close(void)
{
if (statsfd == -1)
return;
munmap(statp, npages *pagesize);
munmap(statp, npages * pagesize);
statp = NULL;
close (statsfd);
statsfd = -1;
@ -63,17 +66,22 @@ void
geom_stats_resync(void)
{
void *p;
off_t mediasize;
int error;
if (statsfd == -1)
return;
for (;;) {
p = mmap(statp, (npages + 1) * pagesize,
PROT_READ, MAP_SHARED, statsfd, 0);
if (p == MAP_FAILED)
break;
else
statp = p;
npages++;
error = ioctl(statsfd, DIOCGMEDIASIZE, &mediasize);
if (error)
err(1, "DIOCGMEDIASIZE(" _PATH_DEV DEVSTAT_DEVICE_NAME ")");
munmap(statp, npages * pagesize);
p = mmap(statp, mediasize, PROT_READ, MAP_SHARED, statsfd, 0);
if (p == MAP_FAILED)
err(1, "mmap(/dev/devstat):");
else {
statp = p;
npages = mediasize / pagesize;
}
}

21
sys/kern/subr_devstat.c
View File

@ -32,6 +32,7 @@
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/disk.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/bio.h>
@ -473,10 +474,12 @@ SYSCTL_INT(_kern_devstat, OID_AUTO, version, CTLFLAG_RD,
#define statsperpage (PAGE_SIZE / sizeof(struct devstat))
static d_ioctl_t devstat_ioctl;
static d_mmap_t devstat_mmap;
static struct cdevsw devstat_cdevsw = {
.d_version = D_VERSION,
.d_ioctl = devstat_ioctl,
.d_mmap = devstat_mmap,
.d_name = "devstat",
};
@ -487,9 +490,26 @@ struct statspage {
u_int nfree;
};
static size_t pagelist_pages = 0;
static TAILQ_HEAD(, statspage) pagelist = TAILQ_HEAD_INITIALIZER(pagelist);
static MALLOC_DEFINE(M_DEVSTAT, "devstat", "Device statistics");
static int
devstat_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int fflag,
struct thread *td)
{
int error = ENOTTY;
switch (cmd) {
case DIOCGMEDIASIZE:
error = 0;
*(off_t *)data = pagelist_pages * PAGE_SIZE;
break;
}
return (error);
}
static int
devstat_mmap(struct cdev *dev, vm_ooffset_t offset, vm_paddr_t *paddr,
int nprot, vm_memattr_t *memattr)
@ -556,6 +576,7 @@ devstat_alloc(void)
* head but the order on the list determine the
* sequence of the mapping so we can't do that.
*/
pagelist_pages++;
TAILQ_INSERT_TAIL(&pagelist, spp, list);
} else
break;