diff mbox series

[block/for-linus] cgroup,writeback: don't switch wbs immediately on dead wbs if the memcg is dead

Message ID 20191108201829.GA3728460@devbig004.ftw2.facebook.com (mailing list archive)
State New, archived
Headers show
Series [block/for-linus] cgroup,writeback: don't switch wbs immediately on dead wbs if the memcg is dead | expand

Commit Message

Tejun Heo Nov. 8, 2019, 8:18 p.m. UTC
cgroup writeback tries to refresh the associated wb immediately if the
current wb is dead.  This is to avoid keeping issuing IOs on the stale
wb after memcg - blkcg association has changed (ie. when blkcg got
disabled / enabled higher up in the hierarchy).

Unfortunately, the logic gets triggered spuriously on inodes which are
associated with dead cgroups.  When the logic is triggered on dead
cgroups, the attempt fails only after doing quite a bit of work
allocating and initializing a new wb.

While c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping
has no dirty pages") alleviated the issue significantly as it now only
triggers when the inode has dirty pages.  However, the condition can
still be triggered before the inode is switched to a different cgroup
and the logic simply doesn't make sense.

Skip the immediate switching if the associated memcg is dying.

This is a simplified version of the following two patches:

 * https://lore.kernel.org/linux-mm/20190513183053.GA73423@dennisz-mbp/
 * http://lkml.kernel.org/r/156355839560.2063.5265687291430814589.stgit@buzz

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: e8a7abf5a5bd ("writeback: disassociate inodes from dying bdi_writebacks")
---
 fs/fs-writeback.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Comments

Dennis Zhou Nov. 8, 2019, 8:33 p.m. UTC | #1
On Fri, Nov 08, 2019 at 12:18:29PM -0800, Tejun Heo wrote:
> cgroup writeback tries to refresh the associated wb immediately if the
> current wb is dead.  This is to avoid keeping issuing IOs on the stale
> wb after memcg - blkcg association has changed (ie. when blkcg got
> disabled / enabled higher up in the hierarchy).
> 
> Unfortunately, the logic gets triggered spuriously on inodes which are
> associated with dead cgroups.  When the logic is triggered on dead
> cgroups, the attempt fails only after doing quite a bit of work
> allocating and initializing a new wb.
> 
> While c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping
> has no dirty pages") alleviated the issue significantly as it now only
> triggers when the inode has dirty pages.  However, the condition can
> still be triggered before the inode is switched to a different cgroup
> and the logic simply doesn't make sense.
> 
> Skip the immediate switching if the associated memcg is dying.
> 
> This is a simplified version of the following two patches:
> 
>  * https://lore.kernel.org/linux-mm/20190513183053.GA73423@dennisz-mbp/
>  * http://lkml.kernel.org/r/156355839560.2063.5265687291430814589.stgit@buzz
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Dennis Zhou <dennis@kernel.org>
> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Fixes: e8a7abf5a5bd ("writeback: disassociate inodes from dying bdi_writebacks")
> ---
>  fs/fs-writeback.c |    9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 8461a6322039..335607b8c5c0 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -576,10 +576,13 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
>  	spin_unlock(&inode->i_lock);
>  
>  	/*
> -	 * A dying wb indicates that the memcg-blkcg mapping has changed
> -	 * and a new wb is already serving the memcg.  Switch immediately.
> +	 * A dying wb indicates that either the blkcg associated with the
> +	 * memcg changed or the associated memcg is dying.  In the first
> +	 * case, a replacement wb should already be available and we should
> +	 * refresh the wb immediately.  In the second case, trying to
> +	 * refresh will keep failing.
>  	 */
> -	if (unlikely(wb_dying(wbc->wb)))
> +	if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
>  		inode_switch_wbs(inode, wbc->wb_id);
>  }
>  EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);

Acked-by: Dennis Zhou <dennis@kernel.org>

Thanks,
Dennis
Jens Axboe Nov. 8, 2019, 8:37 p.m. UTC | #2
On 11/8/19 1:18 PM, Tejun Heo wrote:
> cgroup writeback tries to refresh the associated wb immediately if the
> current wb is dead.  This is to avoid keeping issuing IOs on the stale
> wb after memcg - blkcg association has changed (ie. when blkcg got
> disabled / enabled higher up in the hierarchy).
> 
> Unfortunately, the logic gets triggered spuriously on inodes which are
> associated with dead cgroups.  When the logic is triggered on dead
> cgroups, the attempt fails only after doing quite a bit of work
> allocating and initializing a new wb.
> 
> While c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping
> has no dirty pages") alleviated the issue significantly as it now only
> triggers when the inode has dirty pages.  However, the condition can
> still be triggered before the inode is switched to a different cgroup
> and the logic simply doesn't make sense.
> 
> Skip the immediate switching if the associated memcg is dying.
> 
> This is a simplified version of the following two patches:
> 
>   * https://lore.kernel.org/linux-mm/20190513183053.GA73423@dennisz-mbp/
>   * http://lkml.kernel.org/r/156355839560.2063.5265687291430814589.stgit@buzz

Applied for 5.4, thanks.
Michal Hocko Nov. 11, 2019, 1:15 p.m. UTC | #3
On Fri 08-11-19 12:18:29, Tejun Heo wrote:
> cgroup writeback tries to refresh the associated wb immediately if the
> current wb is dead.  This is to avoid keeping issuing IOs on the stale
> wb after memcg - blkcg association has changed (ie. when blkcg got
> disabled / enabled higher up in the hierarchy).
> 
> Unfortunately, the logic gets triggered spuriously on inodes which are
> associated with dead cgroups.  When the logic is triggered on dead
> cgroups, the attempt fails only after doing quite a bit of work
> allocating and initializing a new wb.
> 
> While c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping
> has no dirty pages") alleviated the issue significantly as it now only
> triggers when the inode has dirty pages.  However, the condition can
> still be triggered before the inode is switched to a different cgroup
> and the logic simply doesn't make sense.
> 
> Skip the immediate switching if the associated memcg is dying.
> 
> This is a simplified version of the following two patches:
> 
>  * https://lore.kernel.org/linux-mm/20190513183053.GA73423@dennisz-mbp/
>  * http://lkml.kernel.org/r/156355839560.2063.5265687291430814589.stgit@buzz
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Dennis Zhou <dennis@kernel.org>
> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Fixes: e8a7abf5a5bd ("writeback: disassociate inodes from dying bdi_writebacks")

Is this a stable material?
Tejun Heo Nov. 11, 2019, 4:18 p.m. UTC | #4
Hello, Michal.

On Mon, Nov 11, 2019 at 02:15:44PM +0100, Michal Hocko wrote:
> > Signed-off-by: Tejun Heo <tj@kernel.org>
> > Cc: Dennis Zhou <dennis@kernel.org>
> > Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > Fixes: e8a7abf5a5bd ("writeback: disassociate inodes from dying bdi_writebacks")
> 
> Is this a stable material?

c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping has
no dirty pages") likely addresses larger part of the problem, but yeah
it prolly makes sense to backport both for -stable.

Greg, Sasha, can you pick the following two commits for -stable?

* c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping has
  no dirty pages")

* 65de03e25138 ("cgroup,writeback: don't switch wbs immediately on
  dead wbs if the memcg is dead")

Both are fixes for e8a7abf5a5bd ("writeback: disassociate inodes from
dying bdi_writebacks") - v4.2+.

Thanks.
Greg Kroah-Hartman Nov. 11, 2019, 4:34 p.m. UTC | #5
On Mon, Nov 11, 2019 at 08:18:16AM -0800, Tejun Heo wrote:
> Hello, Michal.
> 
> On Mon, Nov 11, 2019 at 02:15:44PM +0100, Michal Hocko wrote:
> > > Signed-off-by: Tejun Heo <tj@kernel.org>
> > > Cc: Dennis Zhou <dennis@kernel.org>
> > > Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > > Fixes: e8a7abf5a5bd ("writeback: disassociate inodes from dying bdi_writebacks")
> > 
> > Is this a stable material?
> 
> c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping has
> no dirty pages") likely addresses larger part of the problem, but yeah
> it prolly makes sense to backport both for -stable.
> 
> Greg, Sasha, can you pick the following two commits for -stable?
> 
> * c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping has
>   no dirty pages")
> 
> * 65de03e25138 ("cgroup,writeback: don't switch wbs immediately on
>   dead wbs if the memcg is dead")
> 
> Both are fixes for e8a7abf5a5bd ("writeback: disassociate inodes from
> dying bdi_writebacks") - v4.2+.

Now queued up, thanks.

greg k-h
diff mbox series

Patch

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8461a6322039..335607b8c5c0 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -576,10 +576,13 @@  void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
 	spin_unlock(&inode->i_lock);
 
 	/*
-	 * A dying wb indicates that the memcg-blkcg mapping has changed
-	 * and a new wb is already serving the memcg.  Switch immediately.
+	 * A dying wb indicates that either the blkcg associated with the
+	 * memcg changed or the associated memcg is dying.  In the first
+	 * case, a replacement wb should already be available and we should
+	 * refresh the wb immediately.  In the second case, trying to
+	 * refresh will keep failing.
 	 */
-	if (unlikely(wb_dying(wbc->wb)))
+	if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
 		inode_switch_wbs(inode, wbc->wb_id);
 }
 EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);