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Diffstat (limited to 'lib/orderfiles.c')
| -rw-r--r-- | lib/orderfiles.c | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/lib/orderfiles.c b/lib/orderfiles.c new file mode 100644 index 00000000..1ad955df --- /dev/null +++ b/lib/orderfiles.c @@ -0,0 +1,164 @@ +/* + * orderfiles.c: order file accesses to optimise disk load + * + * Copyright (C) 2014 Colin Watson. + * + * Inspired by and loosely based on dpkg/src/filesdb.c, which is: + * Copyright (C) 1995 Ian Jackson <ian@chiark.greenend.org.uk> + * Copyright (C) 2000,2001 Wichert Akkerman <wakkerma@debian.org> + * Copyright (C) 2008-2014 Guillem Jover <guillem@debian.org> + * + * This file is part of man-db. + * + * man-db is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * man-db is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with man-db; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#ifdef HAVE_CONFIG_H +# include "config.h" +#endif /* HAVE_CONFIG_H */ + +#ifdef HAVE_LINUX_FIEMAP_H +# include <linux/fiemap.h> +# include <linux/fs.h> +# include <sys/ioctl.h> +# include <sys/vfs.h> +#endif /* HAVE_LINUX_FIEMAP_H */ + +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> +#include <stdint.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> + +#include "manconfig.h" + +#include "hashtable.h" + +struct hashtable *physical_offsets = NULL; + +#if defined(HAVE_LINUX_FIEMAP_H) +int compare_physical_offsets (const void *a, const void *b) +{ + const char *left = *(const char **) a; + const char *right = *(const char **) b; + uint64_t *left_offset_p = hashtable_lookup (physical_offsets, + left, strlen (left)); + uint64_t *right_offset_p = hashtable_lookup (physical_offsets, + right, strlen (right)); + uint64_t left_offset = left_offset_p ? *left_offset_p : UINT64_MAX; + uint64_t right_offset = right_offset_p ? *right_offset_p : UINT64_MAX; + + if (left_offset < right_offset) + return -1; + else if (left_offset > right_offset) + return 1; + else + return 0; +} + +void order_files (const char *dir, char **basenames, size_t n_basenames) +{ + int dir_fd_open_flags; + int dir_fd; + struct statfs fs; + size_t i; + + dir_fd_open_flags = O_SEARCH | O_DIRECTORY; +#ifdef O_PATH + dir_fd_open_flags |= O_PATH; +#endif + dir_fd = open (dir, dir_fd_open_flags); + if (dir_fd < 0) + return; + + if (fstatfs (dir_fd, &fs) < 0) { + close (dir_fd); + return; + } + + /* Sort files by the physical locations of their first blocks, in an + * attempt to minimise disk drive head movements. This assumes that + * files are small enough that they are likely to be in one block or + * a small number of contiguous blocks, which seems a reasonable + * assumption for manual pages. + */ + physical_offsets = hashtable_create (plain_hashtable_free); + for (i = 0; i < n_basenames; ++i) { + struct { + struct fiemap fiemap; + struct fiemap_extent extent; + } fm; + int fd; + + fd = openat (dir_fd, basenames[i], O_RDONLY); + if (fd < 0) + continue; + + memset (&fm, 0, sizeof (fm)); + fm.fiemap.fm_start = 0; + fm.fiemap.fm_length = fs.f_bsize; + fm.fiemap.fm_flags = 0; + fm.fiemap.fm_extent_count = 1; + + if (ioctl (fd, FS_IOC_FIEMAP, (unsigned long) &fm) == 0) { + uint64_t *offset = XMALLOC (uint64_t); + *offset = fm.fiemap.fm_extents[0].fe_physical; + hashtable_install (physical_offsets, basenames[i], + strlen (basenames[i]), offset); + } + + close (fd); + } + qsort (basenames, n_basenames, sizeof *basenames, + compare_physical_offsets); + hashtable_free (physical_offsets); + physical_offsets = NULL; + close (dir_fd); +} +#elif defined(HAVE_POSIX_FADVISE) +void order_files (const char *dir, char **basenames, size_t n_basenames) +{ + int dir_fd_open_flags; + int dir_fd; + size_t i; + + dir_fd_open_flags = O_SEARCH | O_DIRECTORY; +#ifdef O_PATH + dir_fd_open_flags |= O_PATH; +#endif + dir_fd = open (dir, dir_fd_open_flags); + if (dir_fd < 0) + return; + + /* While we can't actually order the files, we can at least ask the + * kernel to preload them. + */ + for (i = 0; i < n_basenames; ++i) { + int fd = openat (dir_fd, basenames[i], O_RDONLY | O_NONBLOCK); + if (fd >= 0) { + posix_fadvise (fd, 0, 0, POSIX_FADV_WILLNEED); + close (fd); + } + } + + close (dir_fd); +} +#else +void order_files (const char *dir, char **basenames, size_t n_basenames) +{ +} +#endif |