[PATCH stable 4.6+] radix-tree: account nodes to memcg only if explicitly requested

[PATCH stable 4.6+] radix-tree: account nodes to memcg only if explicitly requested

[Vladimir Davydov]

Radix trees may be used not only for storing page cache pages, so
unconditionally accounting radix tree nodes to the current memory cgroup
is bad: if a radix tree node is used for storing data shared among
different cgroups we risk pinning dead memory cgroups forever. So let's
only account radix tree nodes if it was explicitly requested by passing
__GFP_ACCOUNT to INIT_RADIX_TREE. Currently, we only want to account
page cache entries, so mark mapping->page_tree so.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>  [4.6+]
---
 fs/inode.c       |  2 +-
 lib/radix-tree.c | 14 ++++++++++----
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 69b8b526c194..b4ff82f3a57d 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -344,7 +344,7 @@ EXPORT_SYMBOL(inc_nlink);
 void address_space_init_once(struct address_space *mapping)
 {
 	memset(mapping, 0, sizeof(*mapping));
-	INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
+	INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC | __GFP_ACCOUNT);
 	spin_lock_init(&mapping->tree_lock);
 	init_rwsem(&mapping->i_mmap_rwsem);
 	INIT_LIST_HEAD(&mapping->private_list);
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1624c4117961..9b9be3ffa1f6 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -228,10 +228,11 @@ radix_tree_node_alloc(struct radix_tree_root *root)
 
 		/*
 		 * Even if the caller has preloaded, try to allocate from the
-		 * cache first for the new node to get accounted.
+		 * cache first for the new node to get accounted to the memory
+		 * cgroup.
 		 */
 		ret = kmem_cache_alloc(radix_tree_node_cachep,
-				       gfp_mask | __GFP_ACCOUNT | __GFP_NOWARN);
+				       gfp_mask | __GFP_NOWARN);
 		if (ret)
 			goto out;
 
@@ -254,8 +255,7 @@ radix_tree_node_alloc(struct radix_tree_root *root)
 		kmemleak_update_trace(ret);
 		goto out;
 	}
-	ret = kmem_cache_alloc(radix_tree_node_cachep,
-			       gfp_mask | __GFP_ACCOUNT);
+	ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
 out:
 	BUG_ON(radix_tree_is_indirect_ptr(ret));
 	return ret;
@@ -302,6 +302,12 @@ static int __radix_tree_preload(gfp_t gfp_mask)
 	struct radix_tree_node *node;
 	int ret = -ENOMEM;
 
+	/*
+	 * Nodes preloaded by one cgroup can be be used by another cgroup, so
+	 * they should never be accounted to any particular memory cgroup.
+	 */
+	gfp_mask &= ~__GFP_ACCOUNT;
+
 	preempt_disable();
 	rtp = this_cpu_ptr(&radix_tree_preloads);
 	while (rtp->nr < RADIX_TREE_PRELOAD_SIZE) {
-- 
2.1.4

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Re: [PATCH stable 4.6+] radix-tree: account nodes to memcg only if explicitly requested

[Greg KH]

On Tue, Aug 02, 2016 at 03:45:34PM +0300, Vladimir Davydov wrote:
> Radix trees may be used not only for storing page cache pages, so
> unconditionally accounting radix tree nodes to the current memory cgroup
> is bad: if a radix tree node is used for storing data shared among
> different cgroups we risk pinning dead memory cgroups forever. So let's
> only account radix tree nodes if it was explicitly requested by passing
> __GFP_ACCOUNT to INIT_RADIX_TREE. Currently, we only want to account
> page cache entries, so mark mapping->page_tree so.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: <stable@vger.kernel.org>  [4.6+]
> ---
>  fs/inode.c       |  2 +-
>  lib/radix-tree.c | 14 ++++++++++----
>  2 files changed, 11 insertions(+), 5 deletions(-)

Is this patch in Linus's tree already?

confused,

greg k-h

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Re: [PATCH stable 4.6+] radix-tree: account nodes to memcg only if explicitly requested

[Vladimir Davydov]

On Wed, Aug 03, 2016 at 05:51:39AM +0200, Greg KH wrote:
> On Tue, Aug 02, 2016 at 03:45:34PM +0300, Vladimir Davydov wrote:
> > Radix trees may be used not only for storing page cache pages, so
> > unconditionally accounting radix tree nodes to the current memory cgroup
> > is bad: if a radix tree node is used for storing data shared among
> > different cgroups we risk pinning dead memory cgroups forever. So let's
> > only account radix tree nodes if it was explicitly requested by passing
> > __GFP_ACCOUNT to INIT_RADIX_TREE. Currently, we only want to account
> > page cache entries, so mark mapping->page_tree so.
> > 
> > Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> > Acked-by: Michal Hocko <mhocko@suse.com>
> > Cc: <stable@vger.kernel.org>  [4.6+]
> > ---
> >  fs/inode.c       |  2 +-
> >  lib/radix-tree.c | 14 ++++++++++----
> >  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> Is this patch in Linus's tree already?

Not yet, it should only be added to 4.8, so I shouldn't have sent this
(didn't know how patches are submitted to stable). Please ignore.

> 
> confused,

Sorry for the noise.

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Re: [PATCH stable 4.6+] radix-tree: account nodes to memcg only if explicitly requested

[Greg KH]

On Wed, Aug 03, 2016 at 11:15:25AM +0300, Vladimir Davydov wrote:
> On Wed, Aug 03, 2016 at 05:51:39AM +0200, Greg KH wrote:
> > On Tue, Aug 02, 2016 at 03:45:34PM +0300, Vladimir Davydov wrote:
> > > Radix trees may be used not only for storing page cache pages, so
> > > unconditionally accounting radix tree nodes to the current memory cgroup
> > > is bad: if a radix tree node is used for storing data shared among
> > > different cgroups we risk pinning dead memory cgroups forever. So let's
> > > only account radix tree nodes if it was explicitly requested by passing
> > > __GFP_ACCOUNT to INIT_RADIX_TREE. Currently, we only want to account
> > > page cache entries, so mark mapping->page_tree so.
> > > 
> > > Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> > > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> > > Acked-by: Michal Hocko <mhocko@suse.com>
> > > Cc: <stable@vger.kernel.org>  [4.6+]
> > > ---
> > >  fs/inode.c       |  2 +-
> > >  lib/radix-tree.c | 14 ++++++++++----
> > >  2 files changed, 11 insertions(+), 5 deletions(-)
> > 
> > Is this patch in Linus's tree already?
> 
> Not yet, it should only be added to 4.8, so I shouldn't have sent this
> (didn't know how patches are submitted to stable). Please ignore.

Please read Documentation/stable_kernel_rules.txt, it should help answer
this question (hint, you almost got it right...)

thanks,

greg k-h

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