Messages in this thread | | | Subject | [BUG] fadvise POSIX_FADV_NOREUSE does nothing | From | Eric St-Laurent <> | Date | Sun, 29 Jul 2007 03:57:17 -0400 |
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Related to my other bug report today, calling posix_fadvise (which uses fadvise64) with the POSIX_FADV_NOREUSE flag does nothing. The pages are not dropped behind.
I also tried call fadvise with POSIX_FADV_SEQUENTIAL first.
This is expected as the POSIX_FADV_NOREUSE is a no-op in the recent kernels.
Also, POSIX_FADV_SEQUENTIAL only does the readahead window. It doesn't hint the VM in any way to possibly drop-behind the pages.
(See the previous bug report for more details of the test case)
Relevant numbers:
Copying (using fadvise_cp) a large file test:
1st run: 0m9.018s 2nd run: 0m3.444s Copying large file... 3rd run: 0m14.024s <<< page cache trashed 4th run: 0m3.449s
Test programs and batch files are attached.
- Eric
#include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h>
int main(int argc, char *argv[]) { int in; int out; int pagesize; void *buf; off_t pos;
if (argc != 3) { printf("Usage: %s <src> <dest>\n", argv[0]); return EXIT_FAILURE; }
in = open(argv[1], O_RDONLY, 0); out = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC, 0666);
posix_fadvise(in, 0, 0, POSIX_FADV_SEQUENTIAL); posix_fadvise(out, 0, 0, POSIX_FADV_SEQUENTIAL);
pagesize = getpagesize(); buf = malloc(pagesize);
pos = 0;
for (;;) { ssize_t count;
count = read(in, buf, pagesize); if (!count || count == -1) break;
write(out, buf, count);
/* right usage pattern? */ posix_fadvise(in, pos, count, POSIX_FADV_NOREUSE); posix_fadvise(out, pos, count, POSIX_FADV_NOREUSE);
pos += count; }
free(buf); close(in); close(out);
return EXIT_SUCCESS; } all: gcc fadvise_cp.c -o fadvise_cp gcc working_set_simul.c -o working_set_simul
[unhandled content-type:application/x-shellscript]#include <fcntl.h> #include <memory.h> #include <stdio.h> #include <stdlib.h> #include <sys/mman.h> #include <unistd.h>
int main(int argc, char *argv[]) { int fd; off_t size; char *mapping; unsigned r; unsigned i;
if (argc != 2) { printf("Usage: %s <file>\n", argv[0]); return EXIT_FAILURE; }
fd = open(argv[1], O_RDONLY, 0); size = lseek(fd, 0, SEEK_END);
mapping = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
/* access (read) the file a couple of times*/ for (r = 0; r < 4; r++) { for (i = 0; i < size; i++) { char t = mapping[i]; } }
munmap(mapping, size); close(fd);
return EXIT_SUCCESS; }
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