[PATCH v3 3/7] mm/swap: always account swapped in page into current memcg

[Kairui Song]

From: Kairui Song <kasong@xxxxxxxxxxx>

Currently, mem_cgroup_swapin_charge_folio is always called with
mm == NULL, except in swapin_direct.

swapin_direct is only used when swapin should skip readahead
and swapcache (SWP_SYNCHRONOUS_IO). All other callers of
mem_cgroup_swapin_charge_folio are for swapin that should
not skip readahead and cache.

This could cause swapin charging to behave differently depending
on swap device, which is unexpected.

This is currently not happening because the only caller of
swapin_direct is the direct anon page fault path, where mm always
equals to current->mm, but will no longer be true if swapin_direct
is shared and have other callers (eg, swapoff) to share the
readahead skipping logic.

So make swapin_direct also pass NULL for mm, so swpain charge
will behave consistently and not effected by type of swapin device
or readahead policy.

After this, the second param of mem_cgroup_swapin_charge_folio is
never used now, so it can be safely dropped.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 include/linux/memcontrol.h | 4 ++--
 mm/memcontrol.c            | 5 ++---
 mm/swap_state.c            | 7 +++----
 3 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 20ff87f8e001..540590d80958 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -693,7 +693,7 @@ static inline int mem_cgroup_charge(struct folio *folio, struct mm_struct *mm,
 int mem_cgroup_hugetlb_try_charge(struct mem_cgroup *memcg, gfp_t gfp,
 		long nr_pages);
 
-int mem_cgroup_swapin_charge_folio(struct folio *folio, struct mm_struct *mm,
+int mem_cgroup_swapin_charge_folio(struct folio *folio,
 				  gfp_t gfp, swp_entry_t entry);
 void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry);
 
@@ -1281,7 +1281,7 @@ static inline int mem_cgroup_hugetlb_try_charge(struct mem_cgroup *memcg,
 }
 
 static inline int mem_cgroup_swapin_charge_folio(struct folio *folio,
-			struct mm_struct *mm, gfp_t gfp, swp_entry_t entry)
+		gfp_t gfp, swp_entry_t entry)
 {
 	return 0;
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e4c8735e7c85..5852742df958 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7306,8 +7306,7 @@ int mem_cgroup_hugetlb_try_charge(struct mem_cgroup *memcg, gfp_t gfp,
  *
  * Returns 0 on success. Otherwise, an error code is returned.
  */
-int mem_cgroup_swapin_charge_folio(struct folio *folio, struct mm_struct *mm,
-				  gfp_t gfp, swp_entry_t entry)
+int mem_cgroup_swapin_charge_folio(struct folio *folio, gfp_t gfp, swp_entry_t entry)
 {
 	struct mem_cgroup *memcg;
 	unsigned short id;
@@ -7320,7 +7319,7 @@ int mem_cgroup_swapin_charge_folio(struct folio *folio, struct mm_struct *mm,
 	rcu_read_lock();
 	memcg = mem_cgroup_from_id(id);
 	if (!memcg || !css_tryget_online(&memcg->css))
-		memcg = get_mem_cgroup_from_mm(mm);
+		memcg = get_mem_cgroup_from_current();
 	rcu_read_unlock();
 
 	ret = charge_memcg(folio, memcg, gfp);
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 645f5bcad123..a450d09fc0db 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -495,7 +495,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 	__folio_set_locked(folio);
 	__folio_set_swapbacked(folio);
 
-	if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp_mask, entry))
+	if (mem_cgroup_swapin_charge_folio(folio, gfp_mask, entry))
 		goto fail_unlock;
 
 	/* May fail (-ENOMEM) if XArray node allocation failed. */
@@ -884,9 +884,8 @@ struct folio *swapin_direct(swp_entry_t entry, gfp_t gfp_mask,
 		__folio_set_locked(folio);
 		__folio_set_swapbacked(folio);
 
-		if (mem_cgroup_swapin_charge_folio(folio,
-					vma->vm_mm, GFP_KERNEL,
-					entry)) {
+		if (mem_cgroup_swapin_charge_folio(folio, GFP_KERNEL,
+						   entry)) {
 			folio_unlock(folio);
 			folio_put(folio);
 			return NULL;
-- 
2.43.0