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SubjectRe: [PATCH 3/3] dcache: account external names as indirectly reclaimable memory
On Mon, Mar 12, 2018 at 09:17:42PM +0000, Al Viro wrote:
> On Mon, Mar 05, 2018 at 01:37:43PM +0000, Roman Gushchin wrote:
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index 5c7df1df81ff..a0312d73f575 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -273,8 +273,16 @@ static void __d_free(struct rcu_head *head)
> > static void __d_free_external(struct rcu_head *head)
> > {
> > struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
> > - kfree(external_name(dentry));
> > - kmem_cache_free(dentry_cache, dentry);
> > + struct external_name *name = external_name(dentry);
> > + unsigned long bytes;
> > +
> > + bytes = dentry->d_name.len + offsetof(struct external_name, name[1]);
> > + mod_node_page_state(page_pgdat(virt_to_page(name)),
> > + NR_INDIRECTLY_RECLAIMABLE_BYTES,
> > + -kmalloc_size(kmalloc_index(bytes)));
> > +
> > + kfree(name);
> > + kmem_cache_free(dentry_cache, dentry);
> > }
>
> That can't be right - external names can be freed in release_dentry_name_snapshot()
> and copy_name() as well. When do you want kfree_rcu() paths accounted for, BTW?
> At the point where we are freeing them, or where we are scheduling their freeing?

Ah, I see...

I think, it's better to account them when we're actually freeing,
otherwise we will have strange path:
(indirectly) reclaimable -> unreclaimable -> free

Do you agree?

Although it shouldn't be that important in practice.

Thank you!

--

From ad9d6c627c2b9315de1967c40a1f4fa68705cf9e Mon Sep 17 00:00:00 2001
From: Roman Gushchin <guro@fb.com>
Date: Mon, 12 Mar 2018 22:24:28 +0000
Subject: [PATCH] dcache: fix indirectly reclaimable memory accounting
Signed-off-by: Roman Gushchin <guro@fb.com>
---
fs/dcache.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 98826efe22a0..19bc7495a6c4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -266,6 +266,19 @@ static void __d_free(struct rcu_head *head)
kmem_cache_free(dentry_cache, dentry);
}

+static void __d_free_external_name(struct rcu_head *head)
+{
+ struct external_name *name;
+
+ name = container_of(head, struct external_name, u.head);
+
+ mod_node_page_state(page_pgdat(virt_to_page(name)),
+ NR_INDIRECTLY_RECLAIMABLE_BYTES,
+ -ksize(name));
+
+ kfree(name);
+}
+
static void __d_free_external(struct rcu_head *head)
{
struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
@@ -307,7 +320,7 @@ void release_dentry_name_snapshot(struct name_snapshot *name)
struct external_name *p;
p = container_of(name->name, struct external_name, name[0]);
if (unlikely(atomic_dec_and_test(&p->u.count)))
- kfree_rcu(p, u.head);
+ call_rcu(&p->u.head, __d_free_external_name);
}
}
EXPORT_SYMBOL(release_dentry_name_snapshot);
@@ -2769,7 +2782,7 @@ static void copy_name(struct dentry *dentry, struct dentry *target)
dentry->d_name.hash_len = target->d_name.hash_len;
}
if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
- kfree_rcu(old_name, u.head);
+ call_rcu(&old_name->u.head, __d_free_external_name);
}

static void dentry_lock_for_move(struct dentry *dentry, struct dentry *target)
--
2.14.3
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