| 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 |
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
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.
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?
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.
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 --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);
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(-)