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From: lipeifeng@oppo.com
To: lipeifeng@oppo.com,
	21cnbao@gmail.com,
	akpm@linux-foundation.org,
	david@redhat.com,
	osalvador@suse.de,
	willy@infradead.org
Cc: linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	Barry Song <v-songbaohua@oppo.com>
Subject: [PATCH v2 1/2] mm/rmap: provide folio_referenced with the options to try_lock or lock
Date: Fri,  8 Mar 2024 11:11:25 +0800
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From: Peifeng Li <lipeifeng@oppo.com>

The commit 6d4675e60135 ("mm: don't be stuck to rmap lock on reclaim path")
unconditionally switches to try_lock to avoid lock contention. This patch
introduces a parameter to allow folio_referenced to genuinely wait and
hold the lock in certain scenarios.
Before introducing the new context, we always set try_lock to true to
maintain the current behavior of the code.

Signed-off-by: Peifeng Li <lipeifeng@oppo.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 include/linux/rmap.h |  5 +++--
 mm/rmap.c            |  5 +++--
 mm/vmscan.c          | 16 ++++++++++++++--
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b7944a833668..846b2617a9f2 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -623,7 +623,8 @@ static inline int folio_try_share_anon_rmap_pmd(struct folio *folio,
  * Called from mm/vmscan.c to handle paging out
  */
 int folio_referenced(struct folio *, int is_locked,
-			struct mem_cgroup *memcg, unsigned long *vm_flags);
+			struct mem_cgroup *memcg, unsigned long *vm_flags,
+			unsigned int rw_try_lock);
 
 void try_to_migrate(struct folio *folio, enum ttu_flags flags);
 void try_to_unmap(struct folio *, enum ttu_flags flags);
@@ -739,7 +740,7 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio,
 
 static inline int folio_referenced(struct folio *folio, int is_locked,
 				  struct mem_cgroup *memcg,
-				  unsigned long *vm_flags)
+				  unsigned long *vm_flags, unsigned int rw_try_lock)
 {
 	*vm_flags = 0;
 	return 0;
diff --git a/mm/rmap.c b/mm/rmap.c
index 3746a5531018..7d01f81ca587 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -952,6 +952,7 @@ static bool invalid_folio_referenced_vma(struct vm_area_struct *vma, void *arg)
  * @is_locked: Caller holds lock on the folio.
  * @memcg: target memory cgroup
  * @vm_flags: A combination of all the vma->vm_flags which referenced the folio.
+ * @rw_try_lock: if try_lock in rmap_walk
  *
  * Quick test_and_clear_referenced for all mappings of a folio,
  *
@@ -959,7 +960,7 @@ static bool invalid_folio_referenced_vma(struct vm_area_struct *vma, void *arg)
  * the function bailed out due to rmap lock contention.
  */
 int folio_referenced(struct folio *folio, int is_locked,
-		     struct mem_cgroup *memcg, unsigned long *vm_flags)
+		     struct mem_cgroup *memcg, unsigned long *vm_flags, unsigned int rw_try_lock)
 {
 	int we_locked = 0;
 	struct folio_referenced_arg pra = {
@@ -970,7 +971,7 @@ int folio_referenced(struct folio *folio, int is_locked,
 		.rmap_one = folio_referenced_one,
 		.arg = (void *)&pra,
 		.anon_lock = folio_lock_anon_vma_read,
-		.try_lock = true,
+		.try_lock = rw_try_lock ? true : false,
 		.invalid_vma = invalid_folio_referenced_vma,
 	};
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a0e53999a865..509b5e0dffd3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -147,6 +147,9 @@ struct scan_control {
 	/* Always discard instead of demoting to lower tier memory */
 	unsigned int no_demotion:1;
 
+	/* if try_lock in rmap_walk */
+	unsigned int rw_try_lock:1;
+
 	/* Allocation order */
 	s8 order;
 
@@ -850,7 +853,7 @@ static enum folio_references folio_check_references(struct folio *folio,
 	unsigned long vm_flags;
 
 	referenced_ptes = folio_referenced(folio, 1, sc->target_mem_cgroup,
-					   &vm_flags);
+					   &vm_flags, sc->rw_try_lock);
 	referenced_folio = folio_test_clear_referenced(folio);
 
 	/*
@@ -1522,6 +1525,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
 	struct scan_control sc = {
 		.gfp_mask = GFP_KERNEL,
 		.may_unmap = 1,
+		.rw_try_lock = 1,
 	};
 	struct reclaim_stat stat;
 	unsigned int nr_reclaimed;
@@ -2059,7 +2063,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
 
 		/* Referenced or rmap lock contention: rotate */
 		if (folio_referenced(folio, 0, sc->target_mem_cgroup,
-				     &vm_flags) != 0) {
+				     &vm_flags, sc->rw_try_lock) != 0) {
 			/*
 			 * Identify referenced, file-backed active folios and
 			 * give them one more trip around the active list. So
@@ -2114,6 +2118,7 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
 		.may_unmap = 1,
 		.may_swap = 1,
 		.no_demotion = 1,
+		.rw_try_lock = 1,
 	};
 
 	nr_reclaimed = shrink_folio_list(folio_list, pgdat, &sc, &dummy_stat, ignore_references);
@@ -5459,6 +5464,7 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
 		.may_swap = true,
 		.reclaim_idx = MAX_NR_ZONES - 1,
 		.gfp_mask = GFP_KERNEL,
+		.rw_try_lock = 1,
 	};
 
 	buf = kvmalloc(len + 1, GFP_KERNEL);
@@ -6436,6 +6442,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 		.may_writepage = !laptop_mode,
 		.may_unmap = 1,
 		.may_swap = 1,
+		.rw_try_lock = 1,
 	};
 
 	/*
@@ -6481,6 +6488,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
 		.may_unmap = 1,
 		.reclaim_idx = MAX_NR_ZONES - 1,
 		.may_swap = !noswap,
+		.rw_try_lock = 1,
 	};
 
 	WARN_ON_ONCE(!current->reclaim_state);
@@ -6527,6 +6535,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 		.may_unmap = 1,
 		.may_swap = !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP),
 		.proactive = !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE),
+		.rw_try_lock = 1,
 	};
 	/*
 	 * Traverse the ZONELIST_FALLBACK zonelist of the current node to put
@@ -6788,6 +6797,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
 		.gfp_mask = GFP_KERNEL,
 		.order = order,
 		.may_unmap = 1,
+		.rw_try_lock = 1,
 	};
 
 	set_task_reclaim_state(current, &sc.reclaim_state);
@@ -7257,6 +7267,7 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
 		.may_unmap = 1,
 		.may_swap = 1,
 		.hibernation_mode = 1,
+		.rw_try_lock = 1,
 	};
 	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
 	unsigned long nr_reclaimed;
@@ -7415,6 +7426,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 		.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
 		.may_swap = 1,
 		.reclaim_idx = gfp_zone(gfp_mask),
+		.rw_try_lock = 1,
 	};
 	unsigned long pflags;
 
-- 
2.34.1