1 From: Tobi Oetiker tobi{at}oetiker.ch
4 I am using rsync for hard-link backup. I found that there is a
5 major problem with frequent backup filling up the file system cache
6 with all the data from the files being backed up. The effect is
7 that all the other 'sensible' data in the cache gets thrown out in
8 the process. This is rather unfortunate as the performance of the
9 system becomes very bad after running rsync.
11 Some research showed, that
13 posix_fadvise64(fd, 0, 0,POSIX_FADV_DONTNEED);
15 would tell the OS that it should not keep the file in cache. I
16 have written a patch for rsync that adds the
20 option which activates posix_fadvise64.
22 There are some caveats though:
24 * When calling posix_fadvise64 while writing a file, only the
25 part of the cache will be release which has already been
26 written to disk. This means we have to call fdatasync before
27 calling posix_fadvise64 and this will unfortunately slow down
28 operations considerably. On my test system I get 240 KByte/s.
30 The patch has been optimized, so that the impact on large files
31 will be considerably lowered by calling posix_fadvise64 only
32 after a few megabytes have been written.
34 * When reading a file which has been cached *Before* rsync read
35 it, the content of the file will be released from cache never
36 the less, which may not be intended. I have unfortunately not
37 found a method for determining if a file is in cache or not
40 I found that running rsync of an lvm snapshot is a good way
41 around this problem, since the snapshot data is cached
42 separately from the original. It has the additional benefit of
43 making the backups more consistent.
45 * I don't really know the rsync code, so it may be that the patch
46 is calling fadvise for files where this would not be necessary.
48 * The patch is tested only on Linux 2.6.18
50 If you have any input on this, please let me know.
52 You can get the latest edition of the patch from
54 http://tobi.oetiker.ch/patches/
63 * pass --drop-cache on to the remote server
68 @@ -26,6 +26,10 @@ extern int protocol_version;
70 int csum_length = SHORT_SUM_LENGTH; /* initial value */
72 +#ifdef HAVE_POSIX_FADVISE64
73 +#define close(fd) fadv_close(fd)
77 a simple 32 bit checksum that can be upadted from either end
78 (inspired by Mark Adler's Adler-32 checksum)
81 @@ -46,7 +46,13 @@ void close_all(void)
87 +#ifdef HAVE_POSIX_FADVISE64
91 +#ifdef SHUTDOWN_ALL_SOCKETS
92 max_fd = sysconf(_SC_OPEN_MAX) - 1;
93 for (fd = max_fd; fd >= 0; fd--) {
94 if ((ret = do_fstat(fd, &st)) == 0) {
97 @@ -561,7 +561,7 @@ AC_CHECK_FUNCS(waitpid wait4 getcwd strd
98 strlcat strlcpy strtol mallinfo getgroups setgroups geteuid getegid \
99 setlocale setmode open64 lseek64 mkstemp64 mtrace va_copy __va_copy \
100 strerror putenv iconv_open locale_charset nl_langinfo getxattr \
101 - extattr_get_link sigaction sigprocmask setattrlist)
102 + extattr_get_link sigaction sigprocmask setattrlist posix_fadvise64)
104 AC_CHECK_FUNCS(getpgrp tcgetpgrp)
105 if test $ac_cv_func_getpgrp = yes; then
108 @@ -30,6 +30,12 @@ extern int sparse_files;
109 static char last_byte;
110 static size_t sparse_seek = 0;
112 +#ifdef HAVE_POSIX_FADVISE64
113 +#define close(fd) fadv_close(fd)
114 +#define read(fd,buf,len) fadv_read(fd,buf,len)
115 +#define write(fd,buf,len) fadv_write(fd,buf,len)
118 int sparse_end(int f)
123 @@ -114,6 +114,10 @@ static int need_retouch_dir_times;
124 static int need_retouch_dir_perms;
125 static const char *solo_file = NULL;
127 +#ifdef HAVE_POSIX_FADVISE64
128 +#define close(fd) fadv_close(fd)
131 /* For calling delete_item() and delete_dir_contents(). */
132 #define DEL_RECURSE (1<<1) /* recurse */
133 #define DEL_DIR_IS_EMPTY (1<<2) /* internal delete_FUNCTIONS use only */
136 @@ -58,6 +58,7 @@ int preserve_uid = 0;
137 int preserve_gid = 0;
138 int preserve_times = 0;
144 @@ -319,6 +320,9 @@ void usage(enum logcode F)
145 rprintf(F," --backup-dir=DIR make backups into hierarchy based in DIR\n");
146 rprintf(F," --suffix=SUFFIX set backup suffix (default %s w/o --backup-dir)\n",BACKUP_SUFFIX);
147 rprintf(F," -u, --update skip files that are newer on the receiver\n");
148 +#ifdef HAVE_POSIX_FADVISE64
149 + rprintf(F," --drop-cache tell OS to drop caching of file data\n");
151 rprintf(F," --inplace update destination files in-place (SEE MAN PAGE)\n");
152 rprintf(F," --append append data onto shorter files\n");
153 rprintf(F," --append-verify like --append, but with old data in file checksum\n");
154 @@ -522,6 +526,9 @@ static struct poptOption long_options[]
155 {"size-only", 0, POPT_ARG_NONE, &size_only, 0, 0, 0 },
156 {"one-file-system", 'x', POPT_ARG_NONE, 0, 'x', 0, 0 },
157 {"update", 'u', POPT_ARG_NONE, &update_only, 0, 0, 0 },
158 +#ifdef HAVE_POSIX_FADVISE64
159 + {"drop-cache", 0, POPT_ARG_NONE, &drop_cache, 0, 0, 0 },
161 {"existing", 0, POPT_ARG_NONE, &ignore_non_existing, 0, 0, 0 },
162 {"ignore-non-existing",0,POPT_ARG_NONE, &ignore_non_existing, 0, 0, 0 },
163 {"ignore-existing", 0, POPT_ARG_NONE, &ignore_existing, 0, 0, 0 },
164 @@ -1659,6 +1666,11 @@ void server_options(char **args, int *ar
166 args[ac++] = "--sender";
168 +#ifdef HAVE_POSIX_FADVISE64
170 + args[ac++] = "--drop-cache";
178 @@ -62,6 +62,10 @@ static int phase = 0, redoing = 0;
179 /* We're either updating the basis file or an identical copy: */
180 static int updating_basis;
182 +#ifdef HAVE_POSIX_FADVISE64
183 +#define close(fd) fadv_close(fd)
187 * get_tmpname() - create a tmp filename for a given filename
191 @@ -352,6 +352,7 @@ to the detailed description below for a
192 --super receiver attempts super-user activities
193 --fake-super store/recover privileged attrs using xattrs
194 -S, --sparse handle sparse files efficiently
195 + --drop-cache tell OS to drop caching of file data
196 -n, --dry-run show what would have been transferred
197 -W, --whole-file copy files whole (without rsync algorithm)
198 -x, --one-file-system don't cross filesystem boundaries
199 @@ -1014,6 +1015,10 @@ NOTE: Don't use this option when the des
200 filesystem. It doesn't seem to handle seeks over null regions
201 correctly and ends up corrupting the files.
203 +dit(bf(--drop-cache)) Tell the OS to drop the caching of the file data. This
204 +prevents rsync from filling up the filesystem cache. This can sometimes help
205 +to make a system perform better by keeping non-rsync files in the disk cache.
207 dit(bf(-n, --dry-run)) This tells rsync to not do any file transfers,
208 instead it will just report the actions it would have taken.
212 @@ -46,6 +46,10 @@ extern int write_batch;
213 extern struct stats stats;
214 extern struct file_list *cur_flist, *first_flist, *dir_flist;
216 +#ifdef HAVE_POSIX_FADVISE64
217 +#define close(fd) fadv_close(fd)
225 @@ -28,6 +28,7 @@ int am_root = 0;
230 int preserve_perms = 0;
238 extern int module_id;
239 +extern int drop_cache;
240 extern int modify_window;
241 extern int relative_paths;
242 extern int human_readable;
243 @@ -41,6 +42,131 @@ char curr_dir[MAXPATHLEN];
244 unsigned int curr_dir_len;
245 int curr_dir_depth; /* This is only set for a sanitizing daemon. */
247 +#ifdef HAVE_POSIX_FADVISE64
248 +#define FADV_BUFFER_SIZE 1024*1024*16
250 +static struct stat fadv_fd_stat[1024];
251 +static off_t fadv_fd_pos[1024];
252 +static int fadv_fd_init = 0;
253 +static int fadv_max_fd = 0;
254 +static int fadv_close_ring_tail = 0;
255 +static int fadv_close_ring_head = 0;
256 +static int fadv_close_ring_size = 0;
257 +static int fadv_close_ring[1024];
258 +static int fadv_close_buffer_size = 0;
260 +static void fadv_fd_init_func(void)
262 + if (fadv_fd_init == 0) {
265 + if (fadv_max_fd == 0){
266 + fadv_max_fd = sysconf(_SC_OPEN_MAX) - 20;
267 + if (fadv_max_fd < 0)
269 + if (fadv_max_fd > 1000)
270 + fadv_max_fd = 1000;
272 + for (i = 0; i < fadv_max_fd; i++) {
273 + fadv_fd_pos[i] = 0;
274 + fadv_fd_stat[i].st_dev = 0;
275 + fadv_fd_stat[i].st_ino = 0;
280 +static void fadv_drop(int fd, int sync)
285 + /* Trail 1 MB behind in dropping. we do this to make
286 + * sure that the same block or stripe does not have
287 + * to be written twice. */
288 + if (fd > fadv_max_fd)
290 + pos = lseek(fd, 0, SEEK_CUR) - 1024*1024;
291 + fadv_fd_init_func();
293 + if (fadv_fd_stat[fd].st_dev == sb.st_dev
294 + && fadv_fd_stat[fd].st_ino == sb.st_ino) {
295 + if (fadv_fd_pos[fd] < pos - FADV_BUFFER_SIZE) {
297 + /* If the file is not flushed to disk before calling fadvise,
298 + * then the Cache will not be freed and the advise gets ignored
299 + * this does give a severe hit on performance. If only there
300 + * was a way to mark cache so that it gets release once the data
301 + * is written to disk. */
304 + posix_fadvise64(fd, 0, pos, POSIX_FADV_DONTNEED);
305 + fadv_fd_pos[fd] = pos;
308 + fadv_fd_stat[fd].st_dev = sb.st_dev;
309 + fadv_fd_stat[fd].st_ino = sb.st_ino;
310 + fadv_fd_pos[fd] = 0;
314 +ssize_t fadv_write(int fd, const void *buf, size_t count)
316 + int ret = write(fd, buf, count);
322 +ssize_t fadv_read(int fd, void *buf, size_t count)
324 + int ret = read(fd, buf, count);
330 +void fadv_close_all(void)
332 + while (fadv_close_ring_size > 0){
333 + fdatasync(fadv_close_ring[fadv_close_ring_tail]);
334 + posix_fadvise64(fadv_close_ring[fadv_close_ring_tail], 0, 0,POSIX_FADV_DONTNEED);
335 + fadv_close_ring_size--;
336 + close(fadv_close_ring[fadv_close_ring_tail]);
337 + fadv_close_ring_tail = (fadv_close_ring_tail + 1) % fadv_max_fd;
338 + fadv_close_buffer_size = 0;
342 +int fadv_close(int fd)
345 + /* If the file is not flushed to disk before calling fadvise,
346 + * then the Cache will not be freed and the advise gets ignored
347 + * this does give a severe hit on performance. So instead of doing
348 + * it right away, we save us a copy of the filehandle and do it
349 + * some time before we are out of filehandles. This speeds
350 + * up operation for small files massively. It is directly
351 + * related to the number of spare file handles you have. */
352 + int newfd = dup(fd);
353 + int pos = lseek(fd, 0, SEEK_CUR);
354 + fadv_fd_init_func();
355 + fadv_close_buffer_size += pos - fadv_fd_pos[fd];
356 + fadv_close_ring[fadv_close_ring_head] = newfd;
357 + fadv_close_ring_head = (fadv_close_ring_head + 1) % fadv_max_fd;
358 + fadv_close_ring_size ++;
359 + if (fadv_close_ring_size == fadv_max_fd || fadv_close_buffer_size > 1024*1024 ){
360 + /* it seems fastest to drop things 'in groups' */
367 +#define close(fd) fadv_close(fd)
368 +#define read(fd,buf,len) fadv_read(fd,buf,len)
369 +#define write(fd,buf,len) fadv_write(fd,buf,len)
372 /* Set a fd into nonblocking mode. */
373 void set_nonblocking(int fd)