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// SPDX-License-Identifier: GPL-2.0
#include <linux/swap_cgroup.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/swapops.h> /* depends on mm.h include */
static DEFINE_MUTEX(swap_cgroup_mutex);
struct swap_cgroup_ctrl {
struct page **map;
unsigned long length;
spinlock_t lock;
};
static struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
struct swap_cgroup {
unsigned short id;
};
#define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
/*
* SwapCgroup implements "lookup" and "exchange" operations.
* In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
* against SwapCache. At swap_free(), this is accessed directly from swap.
*
* This means,
* - we have no race in "exchange" when we're accessed via SwapCache because
* SwapCache(and its swp_entry) is under lock.
* - When called via swap_free(), there is no user of this entry and no race.
* Then, we don't need lock around "exchange".
*
* TODO: we can push these buffers out to HIGHMEM.
*/
/*
* allocate buffer for swap_cgroup.
*/
static int swap_cgroup_prepare(int type)
{
struct page *page;
struct swap_cgroup_ctrl *ctrl;
unsigned long idx, max;
ctrl = &swap_cgroup_ctrl[type];
for (idx = 0; idx < ctrl->length; idx++) {
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (!page)
goto not_enough_page;
ctrl->map[idx] = page;
if (!(idx % SWAP_CLUSTER_MAX))
cond_resched();
}
return 0;
not_enough_page:
max = idx;
for (idx = 0; idx < max; idx++)
__free_page(ctrl->map[idx]);
return -ENOMEM;
}
static struct swap_cgroup *__lookup_swap_cgroup(struct swap_cgroup_ctrl *ctrl,
pgoff_t offset)
{
struct page *mappage;
struct swap_cgroup *sc;
mappage = ctrl->map[offset / SC_PER_PAGE];
sc = page_address(mappage);
return sc + offset % SC_PER_PAGE;
}
static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
struct swap_cgroup_ctrl **ctrlp)
{
pgoff_t offset = swp_offset(ent);
struct swap_cgroup_ctrl *ctrl;
ctrl = &swap_cgroup_ctrl[swp_type(ent)];
if (ctrlp)
*ctrlp = ctrl;
return __lookup_swap_cgroup(ctrl, offset);
}
/**
* swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
* @ent: swap entry to be cmpxchged
* @old: old id
* @new: new id
*
* Returns old id at success, 0 at failure.
* (There is no mem_cgroup using 0 as its id)
*/
unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
unsigned short old, unsigned short new)
{
struct swap_cgroup_ctrl *ctrl;
struct swap_cgroup *sc;
unsigned long flags;
unsigned short retval;
sc = lookup_swap_cgroup(ent, &ctrl);
spin_lock_irqsave(&ctrl->lock, flags);
retval = sc->id;
if (retval == old)
sc->id = new;
else
retval = 0;
spin_unlock_irqrestore(&ctrl->lock, flags);
return retval;
}
/**
* swap_cgroup_record - record mem_cgroup for a set of swap entries
* @ent: the first swap entry to be recorded into
* @id: mem_cgroup to be recorded
* @nr_ents: number of swap entries to be recorded
*
* Returns old value at success, 0 at failure.
* (Of course, old value can be 0.)
*/
unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
unsigned int nr_ents)
{
struct swap_cgroup_ctrl *ctrl;
struct swap_cgroup *sc;
unsigned short old;
unsigned long flags;
pgoff_t offset = swp_offset(ent);
pgoff_t end = offset + nr_ents;
sc = lookup_swap_cgroup(ent, &ctrl);
spin_lock_irqsave(&ctrl->lock, flags);
old = sc->id;
for (;;) {
VM_BUG_ON(sc->id != old);
sc->id = id;
offset++;
if (offset == end)
break;
if (offset % SC_PER_PAGE)
sc++;
else
sc = __lookup_swap_cgroup(ctrl, offset);
}
spin_unlock_irqrestore(&ctrl->lock, flags);
return old;
}
/**
* lookup_swap_cgroup_id - lookup mem_cgroup id tied to swap entry
* @ent: swap entry to be looked up.
*
* Returns ID of mem_cgroup at success. 0 at failure. (0 is invalid ID)
*/
unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
{
if (mem_cgroup_disabled())
return 0;
return lookup_swap_cgroup(ent, NULL)->id;
}
int swap_cgroup_swapon(int type, unsigned long max_pages)
{
void *array;
unsigned long length;
struct swap_cgroup_ctrl *ctrl;
if (mem_cgroup_disabled())
return 0;
length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);
array = vcalloc(length, sizeof(void *));
if (!array)
goto nomem;
ctrl = &swap_cgroup_ctrl[type];
mutex_lock(&swap_cgroup_mutex);
ctrl->length = length;
ctrl->map = array;
spin_lock_init(&ctrl->lock);
if (swap_cgroup_prepare(type)) {
/* memory shortage */
ctrl->map = NULL;
ctrl->length = 0;
mutex_unlock(&swap_cgroup_mutex);
vfree(array);
goto nomem;
}
mutex_unlock(&swap_cgroup_mutex);
return 0;
nomem:
pr_info("couldn't allocate enough memory for swap_cgroup\n");
pr_info("swap_cgroup can be disabled by swapaccount=0 boot option\n");
return -ENOMEM;
}
void swap_cgroup_swapoff(int type)
{
struct page **map;
unsigned long i, length;
struct swap_cgroup_ctrl *ctrl;
if (mem_cgroup_disabled())
return;
mutex_lock(&swap_cgroup_mutex);
ctrl = &swap_cgroup_ctrl[type];
map = ctrl->map;
length = ctrl->length;
ctrl->map = NULL;
ctrl->length = 0;
mutex_unlock(&swap_cgroup_mutex);
if (map) {
for (i = 0; i < length; i++) {
struct page *page = map[i];
if (page)
__free_page(page);
if (!(i % SWAP_CLUSTER_MAX))
cond_resched();
}
vfree(map);
}
}
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