linux-kernel - [RFC PATCH 02/28] mm: rcu safe VMA freeing

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Date:   Mon, 29 Aug 2022 21:25:05 +0000
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
        dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com,
        peterz@...radead.org, ldufour@...ux.ibm.com,
        laurent.dufour@...ibm.com, paulmck@...nel.org, riel@...riel.com,
        luto@...nel.org, songliubraving@...com, peterx@...hat.com,
        david@...hat.com, dhowells@...hat.com, hughd@...gle.com,
        bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        rientjes@...gle.com, axelrasmussen@...gle.com, joelaf@...gle.com,
        minchan@...gle.com, surenb@...gle.com, kernel-team@...roid.com,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH 02/28] mm: rcu safe VMA freeing

From: Michel Lespinasse <michel@...pinasse.org>

This prepares for page faults handling under VMA lock, looking up VMAs
under protection of an rcu read lock, instead of the usual mmap read lock.

Signed-off-by: Michel Lespinasse <michel@...pinasse.org>
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 include/linux/mm_types.h | 16 +++++++++++-----
 kernel/fork.c            | 13 +++++++++++++
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index cf97f3884fda..bed25ef7c994 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -403,12 +403,18 @@ struct anon_vma_name {
 struct vm_area_struct {
 	/* The first cache line has the info for VMA tree walking. */
 
-	unsigned long vm_start;		/* Our start address within vm_mm. */
-	unsigned long vm_end;		/* The first byte after our end address
-					   within vm_mm. */
+	union {
+		struct {
+			/* VMA covers [vm_start; vm_end) addresses within mm */
+			unsigned long vm_start, vm_end;
 
-	/* linked list of VM areas per task, sorted by address */
-	struct vm_area_struct *vm_next, *vm_prev;
+			/* linked list of VMAs per task, sorted by address */
+			struct vm_area_struct *vm_next, *vm_prev;
+		};
+#ifdef CONFIG_PER_VMA_LOCK
+		struct rcu_head vm_rcu;	/* Used for deferred freeing. */
+#endif
+	};
 
 	struct rb_node vm_rb;
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 90c85b17bf69..614872438393 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -481,10 +481,23 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
 	return new;
 }
 
+#ifdef CONFIG_PER_VMA_LOCK
+static void __vm_area_free(struct rcu_head *head)
+{
+	struct vm_area_struct *vma = container_of(head, struct vm_area_struct,
+						  vm_rcu);
+	kmem_cache_free(vm_area_cachep, vma);
+}
+#endif
+
 void vm_area_free(struct vm_area_struct *vma)
 {
 	free_anon_vma_name(vma);
+#ifdef CONFIG_PER_VMA_LOCK
+	call_rcu(&vma->vm_rcu, __vm_area_free);
+#else
 	kmem_cache_free(vm_area_cachep, vma);
+#endif
 }
 
 static void account_kernel_stack(struct task_struct *tsk, int account)
-- 
2.37.2.672.g94769d06f0-goog