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zed: implement close_from() in terms of /proc/self/fd, if available

Browse Source 
/dev/fd on Darwin

Consider the following strace output:
  prlimit64(0, RLIMIT_NOFILE, NULL, {rlim_cur=1024, rlim_max=1024*1024}) = 0

Yes, that is well over a million file descriptors!

This reduces the ZED start-up time from "at least a second" to
"instantaneous", and, under strace, from "don't even try" to "usable"
by simple virtue of doing five syscalls instead of over a million;
in most cases the main loop does nothing

Recent Linuxes (5.8+) have close_range(2) for this, but that's an
overoptimisation (and libcs don't have wrappers for it yet)

This is also run by the ZEDLET pre-exec. Compare:
  Finished "all-syslog.sh" eid=13 pid=6717 time=1.027100s exit=0
  Finished "history_event-zfs-list-cacher.sh" eid=13 pid=6718 time=1.046923s exit=0
to
  Finished "all-syslog.sh" eid=12 pid=4834 time=0.001836s exit=0
  Finished "history_event-zfs-list-cacher.sh" eid=12 pid=4835 time=0.001346s exit=0
lol

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #11834
This commit is contained in:
наб 2021-04-02 15:10:34 +02:00 committed by Brian Behlendorf
parent 3bc3eef9c3
commit 64c03a0a27
1 changed files with 22 additions and 8 deletions
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30
cmd/zed/zed_file.c
View File

@ -12,6 +12,7 @@
* You may not use this file except in compliance with the license.
*/
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
@ -160,6 +161,13 @@ zed_file_is_locked(int fd)
return (lock.l_pid);
}
#if __APPLE__
#define PROC_SELF_FD "/dev/fd"
#else /* Linux-compatible layout */
#define PROC_SELF_FD "/proc/self/fd"
#endif
/*
* Close all open file descriptors greater than or equal to [lowfd].
* Any errors encountered while closing file descriptors are ignored.
@ -167,17 +175,23 @@ zed_file_is_locked(int fd)
void
zed_file_close_from(int lowfd)
{
const int maxfd_def = 256;
int errno_bak;
static const int maxfd_def = 256;
int errno_bak = errno;
struct rlimit rl;
int maxfd;
int maxfd = 0;
int fd;
DIR *fddir;
struct dirent *fdent;
errno_bak = errno;
if (getrlimit(RLIMIT_NOFILE, &rl) < 0) {
maxfd = maxfd_def;
} else if (rl.rlim_max == RLIM_INFINITY) {
if ((fddir = opendir(PROC_SELF_FD)) != NULL) {
while ((fdent = readdir(fddir)) != NULL) {
fd = atoi(fdent->d_name);
if (fd > maxfd && fd != dirfd(fddir))
maxfd = fd;
}
(void) closedir(fddir);
} else if (getrlimit(RLIMIT_NOFILE, &rl) < 0 ||
rl.rlim_max == RLIM_INFINITY) {
maxfd = maxfd_def;
} else {
maxfd = rl.rlim_max;