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fallocate: use POSIX_FADV_DONTNEED to discard cached data 

The patch discard cached data in 1MiB (or bigger) steps.

Thanks to Pádraig Brady.

Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2014-02-18 13:01:52 +01:00
parent db5f00bc88
commit c12eff4ce0
1 changed files with 27 additions and 3 deletions
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30
sys-utils/fallocate.c
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@ -134,16 +134,28 @@ static void dig_holes(int fd, off_t off, off_t len)
{
off_t end = len ? off + len : 0;
off_t hole_start = 0, hole_sz = 0;
off_t cache_start = 0;
uintmax_t ct = 0;
size_t bufsz;
size_t bufsz, cachesz;
char *buf, *empty;
struct stat st;
int sparse = 0;
if (fstat(fd, &st) != 0)
err(EXIT_FAILURE, _("stat failed %s"), filename);
bufsz = st.st_blksize;
/*
* We don't want to call POSIX_FADV_DONTNEED to discard cached
* data in PAGE_SIZE steps. IMHO it's overkill (too many syscalls).
*
* Let's assume that 1MiB (on system with 4K page size) is just
* a good compromise.
* -- kzak Feb-2014
*/
cachesz = getpagesize() * 256;
if (st.st_blocks * 512 < st.st_size) {
if (verbose)
fprintf(stdout, _("%s: already has holes.\n"), filename);
@ -154,9 +166,10 @@ static void dig_holes(int fd, off_t off, off_t len)
buf = xmalloc(bufsz);
empty = xcalloc(1, bufsz);
cache_start = off;
#if defined(POSIX_FADV_SEQUENTIAL) && defined(POSIX_FADV_NOREUSE) && defined(HAVE_POSIX_FADVISE)
posix_fadvise(fd, off, 0, POSIX_FADV_SEQUENTIAL | POSIX_FADV_NOREUSE);
#if defined(POSIX_FADV_SEQUENTIAL) && defined(HAVE_POSIX_FADVISE)
posix_fadvise(fd, off, 0, POSIX_FADV_SEQUENTIAL);
#endif
while (end == 0 || off < end) {
@ -188,6 +201,17 @@ static void dig_holes(int fd, off_t off, off_t len)
ct += hole_sz;
hole_sz = hole_start = 0;
}
#if defined(POSIX_FADV_DONTNEED) && defined(HAVE_POSIX_FADVISE)
/* discard cached data */
if (off - cache_start > (off_t) cachesz) {
size_t clen = off - cache_start;
clen = (clen / cachesz) * cachesz;
posix_fadvise(fd, cache_start, clen, POSIX_FADV_DONTNEED);
cache_start = cache_start + clen;
}
#endif
off += rsz;
}