On Wed, 14 Oct 2020 at 14:29, Mateusz Guzik <mjgu...@gmail.com> wrote: > > This should use copy_file_range (also available on Linux). >
I agree. I even mentioned this in https://reviews.freebsd.org/D26041#589287. This change avoids the two unnecessary syscalls, but I agree that longer-term install should share the copy_file_range code with cp. The only thing that copy_file_range won't speed up is the check whether source and target are already identical. Alex > On 10/14/20, Alex Richardson <arichard...@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); > > } > > _______________________________________________ > > svn-src-...@freebsd.org mailing list > > https://lists.freebsd.org/mailman/listinfo/svn-src-all > > To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org" > > > > > -- > Mateusz Guzik <mjguzik gmail.com> _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
