linux-kernel - [PATCH v1 5/6] memcg-v1: no need for memcg locking for MGLRU

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Message-ID: <20241025012304.2473312-6-shakeel.butt@linux.dev>
Date: Thu, 24 Oct 2024 18:23:02 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Hugh Dickins <hughd@...gle.com>,
	Yosry Ahmed <yosryahmed@...gle.com>,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: [PATCH v1 5/6] memcg-v1: no need for memcg locking for MGLRU

While updating the generation of the folios, MGLRU requires that the
folio's memcg association remains stable. With the charge migration
deprecated, there is no need for MGLRU to acquire locks to keep the
folio and memcg association stable.

Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
---
 mm/vmscan.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 29c098790b01..fd7171658b63 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3662,10 +3662,6 @@ static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
 		if (walk->seq != max_seq)
 			break;
 
-		/* folio_update_gen() requires stable folio_memcg() */
-		if (!mem_cgroup_trylock_pages(memcg))
-			break;
-
 		/* the caller might be holding the lock for write */
 		if (mmap_read_trylock(mm)) {
 			err = walk_page_range(mm, walk->next_addr, ULONG_MAX, &mm_walk_ops, walk);
@@ -3673,8 +3669,6 @@ static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
 			mmap_read_unlock(mm);
 		}
 
-		mem_cgroup_unlock_pages();
-
 		if (walk->batched) {
 			spin_lock_irq(&lruvec->lru_lock);
 			reset_batch_size(walk);
@@ -4096,10 +4090,6 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 		}
 	}
 
-	/* folio_update_gen() requires stable folio_memcg() */
-	if (!mem_cgroup_trylock_pages(memcg))
-		return true;
-
 	arch_enter_lazy_mmu_mode();
 
 	pte -= (addr - start) / PAGE_SIZE;
@@ -4144,7 +4134,6 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 	}
 
 	arch_leave_lazy_mmu_mode();
-	mem_cgroup_unlock_pages();
 
 	/* feedback from rmap walkers to page table walkers */
 	if (mm_state && suitable_to_scan(i, young))
-- 
2.43.5