mm: swap: swap ratio support
Add support to receive a static ratio from userspace to
divide the swap pages between ZRAM and disk based swap
devices. The existing infrastructure allows to keep
same priority for multiple swap devices, which results
in round robin distribution of pages. With this patch,
the ratio can be defined.
Change-Id: I54f54489db84cabb206569dd62d61a8a7a898991
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
diff --git a/mm/swap_ratio.c b/mm/swap_ratio.c
new file mode 100644
index 0000000..242cdf6
--- /dev/null
+++ b/mm/swap_ratio.c
@@ -0,0 +1,187 @@
+/*
+ * Copyright (c) 2015, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/mm_types.h>
+#include <linux/swapfile.h>
+#include <linux/swap.h>
+
+#define SWAP_RATIO_GROUP_START (SWAP_FLAG_PRIO_MASK - 9) /* 32758 */
+#define SWAP_RATIO_GROUP_END (SWAP_FLAG_PRIO_MASK) /* 32767 */
+#define SWAP_FAST_WRITES (SWAPFILE_CLUSTER * (SWAP_CLUSTER_MAX / 8))
+#define SWAP_SLOW_WRITES SWAPFILE_CLUSTER
+
+/*
+ * The fast/slow swap write ratio.
+ * 100 indicates that all writes should
+ * go to fast swap device.
+ */
+int sysctl_swap_ratio = 100;
+
+/* Enable the swap ratio feature */
+int sysctl_swap_ratio_enable;
+
+static bool is_same_group(struct swap_info_struct *a,
+ struct swap_info_struct *b)
+{
+ if (!sysctl_swap_ratio_enable)
+ return false;
+
+ if (!is_swap_ratio_group(a->prio))
+ return false;
+
+ if (a->prio == b->prio)
+ return true;
+
+ return false;
+}
+
+/* Caller must hold swap_avail_lock */
+static int calculate_write_pending(struct swap_info_struct *si,
+ struct swap_info_struct *n)
+{
+ int ratio = sysctl_swap_ratio;
+
+ if ((ratio < 0) || (ratio > 100))
+ return -EINVAL;
+
+ if (WARN_ON(!(si->flags & SWP_FAST)))
+ return -ENODEV;
+
+ if ((n->flags & SWP_FAST) || !is_same_group(si, n))
+ return -ENODEV;
+
+ si->max_writes = ratio ? SWAP_FAST_WRITES : 0;
+ n->max_writes = ratio ? (SWAP_FAST_WRITES * 100) /
+ ratio - SWAP_FAST_WRITES : SWAP_SLOW_WRITES;
+
+ si->write_pending = si->max_writes;
+ n->write_pending = n->max_writes;
+
+ return 0;
+}
+
+static int swap_ratio_slow(struct swap_info_struct **si)
+{
+ struct swap_info_struct *n = NULL;
+ int ret = 0;
+
+ spin_lock(&(*si)->lock);
+ spin_lock(&swap_avail_lock);
+ if (&(*si)->avail_list == plist_last(&swap_avail_head)) {
+ /* just to make skip work */
+ n = *si;
+ ret = -ENODEV;
+ goto skip;
+ }
+ n = plist_next_entry(&(*si)->avail_list,
+ struct swap_info_struct,
+ avail_list);
+ spin_unlock(&swap_avail_lock);
+ spin_lock(&n->lock);
+ spin_lock(&swap_avail_lock);
+
+ if ((*si)->flags & SWP_FAST) {
+ if ((*si)->write_pending) {
+ (*si)->write_pending--;
+ goto exit;
+ } else {
+ if ((n->flags & SWP_FAST) || !is_same_group(*si, n)) {
+ /* Should never happen */
+ ret = -ENODEV;
+ } else if (n->write_pending) {
+ /*
+ * Requeue fast device, since there are pending
+ * writes for slow device.
+ */
+ plist_requeue(&(*si)->avail_list,
+ &swap_avail_head);
+ n->write_pending--;
+ spin_unlock(&(*si)->lock);
+ *si = n;
+ goto skip;
+ } else {
+ if (calculate_write_pending(*si, n) < 0) {
+ ret = -ENODEV;
+ goto exit;
+ }
+ /* Restart from fast device */
+ (*si)->write_pending--;
+ }
+ }
+ } else {
+ if (!(n->flags & SWP_FAST) || !is_same_group(*si, n)) {
+ /* Should never happen */
+ ret = -ENODEV;
+ } else if (n->write_pending) {
+ /*
+ * Pending writes for fast device.
+ * We reach here when slow device is swapped on first,
+ * before fast device.
+ */
+ /* requeue slow device to the end */
+ plist_requeue(&(*si)->avail_list, &swap_avail_head);
+ n->write_pending--;
+ spin_unlock(&(*si)->lock);
+ *si = n;
+ goto skip;
+ } else {
+ if ((*si)->write_pending) {
+ (*si)->write_pending--;
+ } else {
+ if (calculate_write_pending(n, *si) < 0) {
+ ret = -ENODEV;
+ goto exit;
+ }
+ n->write_pending--;
+ plist_requeue(&(*si)->avail_list,
+ &swap_avail_head);
+ spin_unlock(&(*si)->lock);
+ *si = n;
+ goto skip;
+ }
+ }
+ }
+exit:
+ spin_unlock(&(*si)->lock);
+skip:
+ spin_unlock(&swap_avail_lock);
+ /* n and si would have got interchanged */
+ spin_unlock(&n->lock);
+ return ret;
+}
+
+bool is_swap_ratio_group(int prio)
+{
+ return ((prio >= SWAP_RATIO_GROUP_START) &&
+ (prio <= SWAP_RATIO_GROUP_END)) ? true : false;
+}
+
+void setup_swap_ratio(struct swap_info_struct *p, int prio)
+{
+ /* Used only if sysctl_swap_ratio_enable is set */
+ if (is_swap_ratio_group(prio)) {
+ if (p->flags & SWP_FAST)
+ p->write_pending = SWAP_FAST_WRITES;
+ else
+ p->write_pending = SWAP_SLOW_WRITES;
+ p->max_writes = p->write_pending;
+ }
+}
+
+int swap_ratio(struct swap_info_struct **si)
+{
+ if (is_swap_ratio_group((*si)->prio))
+ return swap_ratio_slow(si);
+ else
+ return -ENODEV;
+}