On 14 Oct 2020, at 14:28, Mateusz Guzik <mjgu...@gmail.com> wrote: > > This should use copy_file_range (also available on Linux).
I assume this is a bootstrap tool and hence the system OS and version is relevant. macOS does not have copy_file_range, and FreeBSD only has it in -CURRENT so that would break building on 11.x and 12.x. So any use would need to be guarded by preprocessor checks (and there are still actively-supported Linux distributions out there that are based on too-old versions of the kernel and/or glibc to include it). (FYI macOS's equivalent is copyfile(3)... maybe one day it will adopt the copy_file_range(2) interface too) Jess > 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-all@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-all@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"
