svn commit: r366697 - head/usr.bin/xinstall

[Mateusz Guzik]

This should use copy_file_range (also available on Linux).

On 10/14/20, Alex Richardson <arichardson at freebsd.org> wrote:
> Author: arichardson
> Date: Wed Oct 14 12:28:41 2020
> New Revision: 366697
> URL: https://svnweb.freebsd.org/changeset/base/366697
>
> Log:
>   install(1): Avoid unncessary fstatfs() calls and use mmap() based on size
>
>   According to git blame the trymmap() function was added in 1996 to skip
>   mmap() calls for NFS file systems. However, nowadays mmap() should be
>   perfectly safe even on NFS. Importantly, onl ufs and cd9660 file systems
>   were whitelisted so we don't use mmap() on ZFS. It also prevents the use
>   of mmap() when bootstrapping from macOS/Linux since on those systems the
>   trymmap() function was always returning zero due to the missing
> MFSNAMELEN
>   define.
>
>   This change keeps the trymmap() function but changes it to check whether
>   using mmap() can reduce the number of system calls that are required.
>   Using mmap() only reduces the number of system calls if we need multiple
> read()
>   syscalls, i.e. if the file size is > MAXBSIZE. However, mmap() is more
> expensive
>   than read() so this sets the threshold at 4 fewer syscalls. Additionally,
> for
>   larger file size mmap() can significantly increase the number of page
> faults,
>   so avoid it in that case.
>
>   It's unclear whether using mmap() is ever faster than a read with an
> appropriate
>   buffer size, but this change at least removes two unnecessary system
> calls
>   for every file that is installed.
>
>   Reviewed By:	markj
>   Differential Revision: https://reviews.freebsd.org/D26041
>
> Modified:
>   head/usr.bin/xinstall/xinstall.c
>
> Modified: head/usr.bin/xinstall/xinstall.c
> ==============================================================================
> --- head/usr.bin/xinstall/xinstall.c	Wed Oct 14 10:12:39 2020	(r366696)
> +++ head/usr.bin/xinstall/xinstall.c	Wed Oct 14 12:28:41 2020	(r366697)
> @@ -148,7 +148,7 @@ static void	metadata_log(const char *, const char *, s
>  		    const char *, const char *, off_t);
>  static int	parseid(const char *, id_t *);
>  static int	strip(const char *, int, const char *, char **);
> -static int	trymmap(int);
> +static int	trymmap(size_t);
>  static void	usage(void);
>
>  int
> @@ -1087,7 +1087,7 @@ compare(int from_fd, const char *from_name __unused,
> s
>  		if (do_digest)
>  			digest_init(&ctx);
>  		done_compare = 0;
> -		if (trymmap(from_fd) && trymmap(to_fd)) {
> +		if (trymmap(from_len) && trymmap(to_len)) {
>  			p = mmap(NULL, from_len, PROT_READ, MAP_SHARED,
>  			    from_fd, (off_t)0);
>  			if (p == MAP_FAILED)
> @@ -1248,13 +1248,8 @@ copy(int from_fd, const char *from_name, int to_fd,
> co
>
>  	digest_init(&ctx);
>
> -	/*
> -	 * Mmap and write if less than 8M (the limit is so we don't totally
> -	 * trash memory on big files.  This is really a minor hack, but it
> -	 * wins some CPU back.
> -	 */
>  	done_copy = 0;
> -	if (size <= 8 * 1048576 && trymmap(from_fd) &&
> +	if (trymmap((size_t)size) &&
>  	    (p = mmap(NULL, (size_t)size, PROT_READ, MAP_SHARED,
>  		    from_fd, (off_t)0)) != MAP_FAILED) {
>  		nw = write(to_fd, p, size);
> @@ -1523,20 +1518,23 @@ usage(void)
>   *	return true (1) if mmap should be tried, false (0) if not.
>   */
>  static int
> -trymmap(int fd)
> +trymmap(size_t filesize)
>  {
> -/*
> - * The ifdef is for bootstrapping - f_fstypename doesn't exist in
> - * pre-Lite2-merge systems.
> - */
> -#ifdef MFSNAMELEN
> -	struct statfs stfs;
> -
> -	if (fstatfs(fd, &stfs) != 0)
> -		return (0);
> -	if (strcmp(stfs.f_fstypename, "ufs") == 0 ||
> -	    strcmp(stfs.f_fstypename, "cd9660") == 0)
> -		return (1);
> -#endif
> -	return (0);
> +	/*
> +	 * This function existed to skip mmap() for NFS file systems whereas
> +	 * nowadays mmap() should be perfectly safe. Nevertheless, using mmap()
> +	 * only reduces the number of system calls if we need multiple read()
> +	 * syscalls, i.e. if the file size is > MAXBSIZE. However, mmap() is
> +	 * more expensive than read() so set the threshold at 4 fewer syscalls.
> +	 * Additionally, for larger file size mmap() can significantly increase
> +	 * the number of page faults, so avoid it in that case.
> +	 *
> +	 * Note: the 8MB limit is not based on any meaningful benchmarking
> +	 * results, it is simply reusing the same value that was used before
> +	 * and also matches bin/cp.
> +	 *
> +	 * XXX: Maybe we shouldn't bother with mmap() at all, since we use
> +	 * MAXBSIZE the syscall overhead of read() shouldn't be too high?
> +	 */
> +	return (filesize > 4 * MAXBSIZE && filesize < 8 * 1024 * 1024);
>  }
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-- 
Mateusz Guzik <mjguzik gmail.com>