Commit cf4a6553 authored by Shakeel Butt's avatar Shakeel Butt Committed by Andrew Morton
Browse files

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.

[yuzhao@google.com: remove !rcu_read_lock_held() assertion]
  Link: https://lkml.kernel.org/r/ZykEtcHrQRq-KrBC@google.com
  Link: https://syzkaller.appspot.com/bug?extid=24f45b8beab9788e467e
  Link: https://lore.kernel.org/lkml/67294349.050a0220.701a.0010.GAE@google.com/
[akpm@linux-foundation.org: remove now-unused local]
[shakeel.butt@linux.dev: folio_rcu() fixup, per Yu Zhao]
  Link: https://lkml.kernel.org/r/iwmabnye3nl4merealrawt3bdvfii2pwavwrddrqpraoveet7h@ezrsdhjwwej7
Link: https://lkml.kernel.org/r/20241025012304.2473312-6-shakeel.butt@linux.dev


Signed-off-by: default avatarShakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: default avatarRoman Gushchin <roman.gushchin@linux.dev>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 568bcf41

mm/vmscan.c

+1 −15
Original line number Diff line number Diff line
@@ -3137,7 +3137,6 @@ static int folio_update_gen(struct folio *folio, int gen) 
	unsigned long new_flags, old_flags = READ_ONCE(folio->flags);



	VM_WARN_ON_ONCE(gen >= MAX_NR_GENS);

	VM_WARN_ON_ONCE(!rcu_read_lock_held());



	do {

		/* lru_gen_del_folio() has isolated this page? */
@@ -3353,7 +3352,7 @@ static struct folio *get_pfn_folio(unsigned long pfn, struct mem_cgroup *memcg, 
	if (folio_nid(folio) != pgdat->node_id)

		return NULL;



	if (folio_memcg_rcu(folio) != memcg)

	if (folio_memcg(folio) != memcg)

		return NULL;



	/* file VMAs can contain anon pages from COW */
@@ -3649,10 +3648,8 @@ static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk) 
		.p4d_entry = walk_pud_range,

		.walk_lock = PGWALK_RDLOCK,

	};



	int err;

	struct lruvec *lruvec = walk->lruvec;

	struct mem_cgroup *memcg = lruvec_memcg(lruvec);



	walk->next_addr = FIRST_USER_ADDRESS;
@@ -3665,10 +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);
@@ -3676,8 +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);
@@ -4099,10 +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;
@@ -4147,7 +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))