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/*
* Copyright (c) 2016, 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);
if (n == *si) {
/* No other swap device */
ret = -ENODEV;
goto skip;
}
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 (0 > calculate_write_pending(*si, n)) {
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 (0 > calculate_write_pending(n, *si)) {
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 (!sysctl_swap_ratio_enable)
return -ENODEV;
if (is_swap_ratio_group((*si)->prio))
return swap_ratio_slow(si);
else
return -ENODEV;
}
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