[PATCH 3/4] mm/swap_cgroup: simplify swap cgroup definitions

Kairui Song
2024-12-02T18:42:25Z

From: Kairui Song <kasong@tencent.com>

Remove the intermediate struct swap_cgroup, it just a unsigned short
wrapper, simplify the code.

Also zero the map on initialization to prevent unexpected behaviour as
swap cgroup helpers are suppose to return 0 on error.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/swap_cgroup.c | 45 +++++++++++++++++++--------------------------
1 file changed, 19 insertions(+), 26 deletions(-)

diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index 1770b076f6b7..a76afdc3666a 100644
--- a/mm/swap_cgroup.c
+++ b/mm/swap_cgroup.c
@@ -12,14 +12,12 @@ struct swap_cgroup {
};

struct swap_cgroup_ctrl {
- struct swap_cgroup *map;
+ unsigned short *map;
spinlock_t lock;
};

static struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];

-#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
@@ -33,18 +31,6 @@ static struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
*
* TODO: we can push these buffers out to HIGHMEM.
*/
-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 &ctrl->map[offset];
-}
-
/**
* swap_cgroup_record - record mem_cgroup for a set of swap entries
* @ent: the first swap entry to be recorded into
@@ -58,20 +44,21 @@ 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 *map;
unsigned short old;
unsigned long flags;
pgoff_t offset = swp_offset(ent);
pgoff_t end = offset + nr_ents;

- sc = lookup_swap_cgroup(ent, &ctrl);
+ ctrl = &swap_cgroup_ctrl[swp_type(ent)];
+ map = ctrl->map;

spin_lock_irqsave(&ctrl->lock, flags);
- old = sc->id;
- for (; offset < end; offset++, sc++) {
- VM_BUG_ON(sc->id != old);
- sc->id = id;
- }
+ old = map[offset];
+ do {
+ VM_BUG_ON(map[offset] != old);
+ map[offset] = id;
+ } while (++offset != end);
spin_unlock_irqrestore(&ctrl->lock, flags);

return old;
@@ -85,20 +72,26 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
*/
unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
{
+ struct swap_cgroup_ctrl *ctrl;
+
if (mem_cgroup_disabled())
return 0;
- return lookup_swap_cgroup(ent, NULL)->id;
+
+ ctrl = &swap_cgroup_ctrl[swp_type(ent)];
+ pgoff_t offset = swp_offset(ent);
+
+ return READ_ONCE(ctrl->map[offset]);
}

int swap_cgroup_swapon(int type, unsigned long max_pages)
{
- struct swap_cgroup *map;
+ void *map;
struct swap_cgroup_ctrl *ctrl;

if (mem_cgroup_disabled())
return 0;

- map = vcalloc(max_pages, sizeof(struct swap_cgroup));
+ map = vzalloc(max_pages * sizeof(unsigned short));
if (!map)
goto nomem;

@@ -117,7 +110,7 @@ int swap_cgroup_swapon(int type, unsigned long max_pages)

void swap_cgroup_swapoff(int type)
{
- struct swap_cgroup *map;
+ void *map;
struct swap_cgroup_ctrl *ctrl;

if (mem_cgroup_disabled())
--
2.47.0