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)
Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
---
sys-utils/swapon.8 | 24 +++++++++++++------
sys-utils/swapon.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++--------
2 files changed, 77 insertions(+), 17 deletions(-)
diff --git a/sys-utils/swapon.8 b/sys-utils/swapon.8
index 385bf5a..17f7970 100644
--- a/sys-utils/swapon.8
+++ b/sys-utils/swapon.8
@@ -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 long option \-\-discard 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.
diff --git a/sys-utils/swapon.c b/sys-utils/swapon.c
index f1e2433..8a90bfe 100644
--- a/sys-utils/swapon.c
+++ b/sys-utils/swapon.c
@@ -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 = 0; /* don't send swap discards by default */
/* If true, don't complain if the device/file doesn't exist */
static int ifexists;
@@ -570,8 +581,22 @@ 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)
@@ -611,12 +636,22 @@ 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)
@@ -647,7 +682,7 @@ static void __attribute__ ((__noreturn__)) usage(FILE * out)
fputs(USAGE_OPTIONS, out);
fputs(_(" -a, --all enable all swaps from /etc/fstab\n"
- " -d, --discard discard freed pages before they are reused\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"
@@ -672,6 +707,11 @@ 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));
@@ -696,7 +736,7 @@ 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' },
@@ -739,7 +779,17 @@ int main(int argc, char *argv[])
add_uuid(optarg);
break;
case 'd':
- discard = 1;
+ discard |= SWAP_FLAG_DISCARD;
+
+ if (optarg) {
+ /* only single-time discards are wanted */
+ if (strcmp(optarg, "once") == 0)
+ discard |= SWAP_FLAG_DISCARD_ONCE;
+
+ /* do discard for every released swap page */
+ if (strcmp(optarg, "pages") == 0)
+ discard |= SWAP_FLAG_DISCARD_PAGES;
+ }
break;
case 'e': /* ifexists */
ifexists = 1;
--
1.8.1.4
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