[PATCH 2/3] memcg/hugetlb: Introduce mem_cgroup_charge_hugetlb

[Joshua Hahn <joshua.hahnjy@xxxxxxxxx>]

This patch introduces mem_cgroup_charge_hugetlb, which combines the
logic of mem_cgroup{try,commit}_hugetlb. This reduces the footprint of
memcg in hugetlb code, and also consolidates the error path that memcg
can take into just one point.

Signed-off-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>

---
 include/linux/memcontrol.h |  2 ++
 mm/hugetlb.c               | 34 ++++++++++++----------------------
 mm/memcontrol.c            | 19 +++++++++++++++++++
 3 files changed, 33 insertions(+), 22 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index bb49e0d4b377..d90c1ac791f1 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -678,6 +678,8 @@ 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_charge_hugetlb(struct folio* folio, gfp_t gfp);
+
 int mem_cgroup_swapin_charge_folio(struct folio *folio, struct mm_struct *mm,
 				  gfp_t gfp, swp_entry_t entry);
 
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index fbb10e52d7ea..6f6841483039 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2967,21 +2967,13 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 	struct hugepage_subpool *spool = subpool_vma(vma);
 	struct hstate *h = hstate_vma(vma);
 	struct folio *folio;
-	long map_chg, map_commit, nr_pages = pages_per_huge_page(h);
+	long map_chg, map_commit;
 	long gbl_chg;
-	int memcg_charge_ret, ret, idx;
+	int ret, idx;
 	struct hugetlb_cgroup *h_cg = NULL;
-	struct mem_cgroup *memcg;
 	bool deferred_reserve;
 	gfp_t gfp = htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;
 
-	memcg = get_mem_cgroup_from_current();
-	memcg_charge_ret = mem_cgroup_hugetlb_try_charge(memcg, gfp, nr_pages);
-	if (memcg_charge_ret == -ENOMEM) {
-		mem_cgroup_put(memcg);
-		return ERR_PTR(-ENOMEM);
-	}
-
 	idx = hstate_index(h);
 	/*
 	 * Examine the region/reserve map to determine if the process
@@ -2989,12 +2981,8 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 	 * code of zero indicates a reservation exists (no change).
 	 */
 	map_chg = gbl_chg = vma_needs_reservation(h, vma, addr);
-	if (map_chg < 0) {
-		if (!memcg_charge_ret)
-			mem_cgroup_cancel_charge(memcg, nr_pages);
-		mem_cgroup_put(memcg);
+	if (map_chg < 0)
 		return ERR_PTR(-ENOMEM);
-	}
 
 	/*
 	 * Processes that did not create the mapping will have no
@@ -3092,10 +3080,15 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 		}
 	}
 
-	if (!memcg_charge_ret)
-		mem_cgroup_commit_charge(folio, memcg);
-	lruvec_stat_mod_folio(folio, NR_HUGETLB, pages_per_huge_page(h));
-	mem_cgroup_put(memcg);
+	ret = mem_cgroup_charge_hugetlb(folio, gfp);
+	if (ret == -ENOMEM) {
+		spin_unlock_irq(&hugetlb_lock);
+		free_huge_folio(folio);
+		return ERR_PTR(-ENOMEM);
+	}
+	else if (!ret)
+		lruvec_stat_mod_folio(folio, NR_HUGETLB,
+		      pages_per_huge_page(h));
 
 	return folio;
 
@@ -3110,9 +3103,6 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 		hugepage_subpool_put_pages(spool, 1);
 out_end_reservation:
 	vma_end_reservation(h, vma, addr);
-	if (!memcg_charge_ret)
-		mem_cgroup_cancel_charge(memcg, nr_pages);
-	mem_cgroup_put(memcg);
 	return ERR_PTR(-ENOSPC);
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 97f63ec9c9fb..95ee77fe27af 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4529,6 +4529,25 @@ int mem_cgroup_hugetlb_try_charge(struct mem_cgroup *memcg, gfp_t gfp,
 	return 0;
 }
 
+int mem_cgroup_charge_hugetlb(struct folio *folio, gfp_t gfp)
+{
+	struct mem_cgroup *memcg = get_mem_cgroup_from_current();
+	int ret = 0;
+
+	if (mem_cgroup_disabled() || !memcg_accounts_hugetlb() ||
+		!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
+	if (charge_memcg(folio, memcg, gfp))
+		ret = -ENOMEM;
+
+out:
+	mem_cgroup_put(memcg);
+	return ret;
+}
+
 /**
  * mem_cgroup_swapin_charge_folio - Charge a newly allocated folio for swapin.
  * @folio: folio to charge.
-- 
2.43.5