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Replace a single linked list with a hash table of lists.

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mountd.c uses a single linked list of "struct exportlist" structures,
where there is one of these for each exported file system on the NFS server.
This list gets long if there are a large number of file systems exported and
the list must be searched for each line in the exports file(s) when
SIGHUP causes the exports file(s) to be reloaded.
A simple benchmark that traverses SLIST() elements and compares two 32bit
fields in the structure for equal (which is what the search is)
appears to take a couple of nsec. So, for a server with 72000 exported file
systems, this can take about 5sec during reload of the exports file(s).
By replacing the single linked list with a hash table with a target of
10 elements per list, the time should be reduced to less than 1msec.
Peter Errikson (who has a server with 72000+ exported file systems) ran
a test program using 5 hashes to see how they worked.
fnv_32_buf(fsid,..., 0)
fnv_32_buf(fsid,..., FNV1_32_INIT)
hash32_buf(fsid,..., 0)
hash32_buf(fsid,..., HASHINIT)
- plus simply using the low order bits of fsid.val[0].
The first three behaved about equally well, with the first one being
slightly better than the others.
It has an average variation of about 4.5% about the target list length
and that is what this patch uses.
Peter Errikson also tested this hash table version and found that the
performance wasn't measurably improved by a larger hash table, so a
load factor of 10 appears adequate.

Tested by:	pen@lysator.liu.se (with other patches)
PR:		237860
MFC after:	1 month
This commit is contained in:
Rick Macklem 2019-05-31 01:28:48 +00:00
parent 26fd36b29d
commit 46a6b5c451
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=348452
1 changed files with 49 additions and 21 deletions
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70
usr.sbin/mountd/mountd.c
View File

@ -49,6 +49,7 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/fcntl.h>
#include <sys/fnv_hash.h>
#include <sys/linker.h>
#include <sys/module.h>
#include <sys/mount.h>
@ -234,7 +235,9 @@ static int xdr_fhs(XDR *, caddr_t);
static int xdr_mlist(XDR *, caddr_t);
static void terminate(int);
static struct exportlisthead exphead = SLIST_HEAD_INITIALIZER(&exphead);
#define EXPHASH(f) (fnv_32_buf((f), sizeof(fsid_t), 0) % exphashsize)
static struct exportlisthead *exphead = NULL;
static int exphashsize = 0;
static SLIST_HEAD(, mountlist) mlhead = SLIST_HEAD_INITIALIZER(&mlhead);
static char *exnames_default[2] = { _PATH_EXPORTS, NULL };
static char **exnames;
@ -1092,7 +1095,7 @@ mntsrv(struct svc_req *rqstp, SVCXPRT *transp)
if (bad)
ep = NULL;
else
ep = ex_search(&fsb.f_fsid, &exphead);
ep = ex_search(&fsb.f_fsid, exphead);
hostset = defset = 0;
if (ep && (chk_host(ep->ex_defdir, saddr, &defset, &hostset,
&numsecflavors, &secflavorsp) ||
@ -1307,21 +1310,23 @@ xdr_explist_common(XDR *xdrsp, caddr_t cp __unused, int brief)
int false = 0;
int putdef;
sigset_t sighup_mask;
int i;
sigemptyset(&sighup_mask);
sigaddset(&sighup_mask, SIGHUP);
sigprocmask(SIG_BLOCK, &sighup_mask, NULL);
SLIST_FOREACH(ep, &exphead, entries) {
putdef = 0;
if (put_exlist(ep->ex_dirl, xdrsp, ep->ex_defdir,
&putdef, brief))
goto errout;
if (ep->ex_defdir && putdef == 0 &&
put_exlist(ep->ex_defdir, xdrsp, (struct dirlist *)NULL,
&putdef, brief))
goto errout;
}
for (i = 0; i < exphashsize; i++)
SLIST_FOREACH(ep, &exphead[i], entries) {
putdef = 0;
if (put_exlist(ep->ex_dirl, xdrsp, ep->ex_defdir,
&putdef, brief))
goto errout;
if (ep->ex_defdir && putdef == 0 &&
put_exlist(ep->ex_defdir, xdrsp, NULL,
&putdef, brief))
goto errout;
}
sigprocmask(SIG_UNBLOCK, &sighup_mask, NULL);
if (!xdr_bool(xdrsp, &false))
return (0);
@ -1545,7 +1550,7 @@ get_exportlist_one(void)
* See if this directory is already
* in the list.
*/
ep = ex_search(&fsb.f_fsid, &exphead);
ep = ex_search(&fsb.f_fsid, exphead);
if (ep == (struct exportlist *)NULL) {
ep = get_exp();
ep->ex_fs = fsb.f_fsid;
@ -1700,7 +1705,7 @@ get_exportlist_one(void)
}
dirhead = (struct dirlist *)NULL;
if ((ep->ex_flag & EX_LINKED) == 0) {
insert_exports(ep, &exphead);
insert_exports(ep, exphead);
ep->ex_flag |= EX_LINKED;
}
@ -1739,7 +1744,8 @@ get_exportlist(void)
/*
* First, get rid of the old list
*/
free_exports(&exphead);
if (exphead != NULL)
free_exports(exphead);
/*
* and the old V4 root dir.
@ -1762,6 +1768,21 @@ get_exportlist(void)
*/
num = getmntinfo(&mntbufp, MNT_NOWAIT);
/* Allocate hash tables, for first call. */
if (exphead == NULL) {
/* Target an average linked list length of 10. */
exphashsize = num / 10;
if (exphashsize < 1)
exphashsize = 1;
else if (exphashsize > 100000)
exphashsize = 100000;
exphead = malloc(exphashsize * sizeof(*exphead));
if (exphead == NULL)
errx(1, "Can't malloc hash table");
for (i = 0; i < exphashsize; i++)
SLIST_INIT(&exphead[i]);
}
if (num > 0) {
build_iovec(&iov, &iovlen, "fstype", NULL, 0);
build_iovec(&iov, &iovlen, "fspath", NULL, 0);
@ -1806,8 +1827,10 @@ get_exportlist(void)
static void
insert_exports(struct exportlist *ep, struct exportlisthead *exhp)
{
uint32_t i;
SLIST_INSERT_HEAD(exhp, ep, entries);
i = EXPHASH(&ep->ex_fs);
SLIST_INSERT_HEAD(&exhp[i], ep, entries);
}
/*
@ -1817,12 +1840,15 @@ static void
free_exports(struct exportlisthead *exhp)
{
struct exportlist *ep, *ep2;
int i;
SLIST_FOREACH_SAFE(ep, exhp, entries, ep2) {
SLIST_REMOVE(exhp, ep, exportlist, entries);
free_exp(ep);
for (i = 0; i < exphashsize; i++) {
SLIST_FOREACH_SAFE(ep, &exhp[i], entries, ep2) {
SLIST_REMOVE(&exhp[i], ep, exportlist, entries);
free_exp(ep);
}
SLIST_INIT(&exhp[i]);
}
SLIST_INIT(exhp);
}
/*
@ -1962,8 +1988,10 @@ static struct exportlist *
ex_search(fsid_t *fsid, struct exportlisthead *exhp)
{
struct exportlist *ep;
uint32_t i;
SLIST_FOREACH(ep, exhp, entries) {
i = EXPHASH(fsid);
SLIST_FOREACH(ep, &exhp[i], entries) {
if (ep->ex_fs.val[0] == fsid->val[0] &&
ep->ex_fs.val[1] == fsid->val[1])
return (ep);