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swapon: allow a more flexible swap discard policy 

Introduce the necessary changes to swapon(8) allowing a sysadmin to leverage
the new changes introduced to sys_swapon by "swap: discard while swapping
only if SWAP_FLAG_DISCARD_PAGES", therefore allowing a more flexible set of
choices when selection the discard policy for mounted swap areas.
This patch introduces the following optional arguments to the already
existent swapon(8) "--discard" option, in order to allow a discard type to
be selected at swapon time:
 * once    : only single-time area discards are issued. (swapon)
 * pages   : discard freed pages before they are reused.
If no policy is selected both discard types are enabled. (default)

[kzak@redhat.com: - support <policy> argument for short -d option too,
                  - add errx() on unsupported policy name]

Signed-off-by: Rafael Aquini <aquini@redhat.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Rafael Aquini 2013-05-26 01:31:56 -03:00 committed by Karel Zak
parent b86727542f
commit d6387c98cb
2 changed files with 89 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
sys-utils/swapon.8
View File

@ -112,15 +112,25 @@ All devices marked as ``swap'' in
are made available, except for those with the ``noauto'' option.
Devices that are already being used as swap are silently skipped.
.TP
.B "\-d, \-\-discard"
Discard freed swap pages before they are reused, if the swap
device supports the discard or trim operation. This may improve
performance on some Solid State Devices, but often it does not.
.B "\-d, \-\-discard\fR [=\fIpolicy\fR]"
Enable swap discards, if the swap backing device supports the discard or
trim operation. This may improve performance on some Solid State Devices,
but often it does not. The option allows one to select between two
available swap discard policies:
.BI \-\-discard=once
to perform a single-time discard operation for the whole swap area at swapon;
or
.BI \-\-discard=pages
to discard freed swap pages before they are reused, while swapping.
If no policy is selected, the default behavior is to enable both discard types.
The
.I /etc/fstab
mount option
.BI discard
may be also used to enable discard flag.
mount options
.BI discard,
.BI discard=once,
or
.BI discard=pages
may be also used to enable discard flags.
.TP
.B "\-e, \-\-ifexists"
Silently skip devices that do not exist.

93
sys-utils/swapon.c
View File

@ -34,9 +34,20 @@
#endif
#ifndef SWAP_FLAG_DISCARD
# define SWAP_FLAG_DISCARD 0x10000 /* discard swap cluster after use */
# define SWAP_FLAG_DISCARD 0x10000 /* enable discard for swap */
#endif
#ifndef SWAP_FLAG_DISCARD_ONCE
# define SWAP_FLAG_DISCARD_ONCE 0x20000 /* discard swap area at swapon-time */
#endif
#ifndef SWAP_FLAG_DISCARD_PAGES
# define SWAP_FLAG_DISCARD_PAGES 0x40000 /* discard page-clusters after use */
#endif
#define SWAP_FLAGS_DISCARD_VALID (SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE | \
SWAP_FLAG_DISCARD_PAGES)
#ifndef SWAP_FLAG_PREFER
# define SWAP_FLAG_PREFER 0x8000 /* set if swap priority specified */
#endif
@ -70,7 +81,7 @@ enum {
static int all;
static int priority = -1; /* non-prioritized swap by default */
static int discard;
static int discard; /* don't send swap discards by default */
/* If true, don't complain if the device/file doesn't exist */
static int ifexists;
@ -572,8 +583,22 @@ static int do_swapon(const char *orig_special, int prio,
<< SWAP_FLAG_PRIO_SHIFT);
}
#endif
if (fl_discard)
flags |= SWAP_FLAG_DISCARD;
/*
* Validate the discard flags passed and set them
* accordingly before calling sys_swapon.
*/
if (fl_discard && !(fl_discard & ~SWAP_FLAGS_DISCARD_VALID)) {
/*
* If we get here with both discard policy flags set,
* we just need to tell the kernel to enable discards
* and it will do correctly, just as we expect.
*/
if ((fl_discard & SWAP_FLAG_DISCARD_ONCE) &&
(fl_discard & SWAP_FLAG_DISCARD_PAGES))
flags |= SWAP_FLAG_DISCARD;
else
flags |= fl_discard;
}
status = swapon(special, flags);
if (status < 0)
@ -613,12 +638,22 @@ static int swapon_all(void)
while (mnt_table_find_next_fs(tb, itr, match_swap, NULL, &fs) == 0) {
/* defaults */
int pri = priority, dsc = discard, nofail = ifexists;
char *p, *src;
char *p, *src, *dscarg;
if (mnt_fs_get_option(fs, "noauto", NULL, NULL) == 0)
continue;
if (mnt_fs_get_option(fs, "discard", NULL, NULL) == 0)
dsc = 1;
if (mnt_fs_get_option(fs, "discard", &dscarg, NULL) == 0) {
dsc |= SWAP_FLAG_DISCARD;
if (dscarg) {
/* only single-time discards are wanted */
if (strcmp(dscarg, "once") == 0)
dsc |= SWAP_FLAG_DISCARD_ONCE;
/* do discard for every released swap page */
if (strcmp(dscarg, "pages") == 0)
dsc |= SWAP_FLAG_DISCARD_PAGES;
}
}
if (mnt_fs_get_option(fs, "nofail", NULL, NULL) == 0)
nofail = 1;
if (mnt_fs_get_option(fs, "pri", &p, NULL) == 0 && p)
@ -648,17 +683,17 @@ static void __attribute__ ((__noreturn__)) usage(FILE * out)
fprintf(out, _(" %s [options] [<spec>]\n"), program_invocation_short_name);
fputs(USAGE_OPTIONS, out);
fputs(_(" -a, --all enable all swaps from /etc/fstab\n"
" -d, --discard discard freed pages before they are reused\n"
" -e, --ifexists silently skip devices that do not exist\n"
" -f, --fixpgsz reinitialize the swap space if necessary\n"
" -p, --priority <prio> specify the priority of the swap device\n"
" -s, --summary display summary about used swap devices\n"
" --show[=<columns>] display summary in definable table\n"
" --noheadings don't print headings, use with --show\n"
" --raw use the raw output format, use with --show\n"
" --bytes display swap size in bytes in --show output\n"
" -v, --verbose verbose mode\n"), out);
fputs(_(" -a, --all enable all swaps from /etc/fstab\n"
" -d, --discard[=<policy>] enable swap discards, if supported by device\n"
" -e, --ifexists silently skip devices that do not exist\n"
" -f, --fixpgsz reinitialize the swap space if necessary\n"
" -p, --priority <prio> specify the priority of the swap device\n"
" -s, --summary display summary about used swap devices\n"
" --show[=<columns>] display summary in definable table\n"
" --noheadings don't print headings, use with --show\n"
" --raw use the raw output format, use with --show\n"
" --bytes display swap size in bytes in --show output\n"
" -v, --verbose verbose mode\n"), out);
fputs(USAGE_SEPARATOR, out);
fputs(USAGE_HELP, out);
@ -674,6 +709,11 @@ static void __attribute__ ((__noreturn__)) usage(FILE * out)
" <device> name of device to be used\n"
" <file> name of file to be used\n"), out);
fputs(_("\nAvailable discard policy types (for --discard):\n"
" once : only single-time area discards are issued. (swapon)\n"
" pages : discard freed pages before they are reused.\n"
" * if no policy is selected both discard types are enabled. (default)\n"), out);
fputs(_("\nAvailable columns (for --show):\n"), out);
for (i = 0; i < NCOLS; i++)
fprintf(out, " %4s %s\n", infos[i].name, _(infos[i].help));
@ -698,7 +738,7 @@ int main(int argc, char *argv[])
static const struct option long_opts[] = {
{ "priority", 1, 0, 'p' },
{ "discard", 0, 0, 'd' },
{ "discard", 2, 0, 'd' },
{ "ifexists", 0, 0, 'e' },
{ "summary", 0, 0, 's' },
{ "fixpgsz", 0, 0, 'f' },
@ -721,7 +761,7 @@ int main(int argc, char *argv[])
mnt_init_debug(0);
mntcache = mnt_new_cache();
while ((c = getopt_long(argc, argv, "ahdefp:svVL:U:",
while ((c = getopt_long(argc, argv, "ahd::efp:svVL:U:",
long_opts, NULL)) != -1) {
switch (c) {
case 'a': /* all */
@ -741,7 +781,18 @@ int main(int argc, char *argv[])
add_uuid(optarg);
break;
case 'd':
discard = 1;
discard |= SWAP_FLAG_DISCARD;
if (optarg) {
if (*optarg == '=')
optarg++;
if (strcmp(optarg, "once") == 0)
discard |= SWAP_FLAG_DISCARD_ONCE;
else if (strcmp(optarg, "pages") == 0)
discard |= SWAP_FLAG_DISCARD_PAGES;
else
errx(EXIT_FAILURE, _("unsupported discard policy: %s"), optarg);
}
break;
case 'e': /* ifexists */
ifexists = 1;