On Sat, Dec 19, 2020 at 1:48 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> On Sat, Dec 19, 2020 at 12:11 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> >
> > Currently the fs sysctl inotify/max_user_instances is used to limit the
> > number of inotify instances on the system. For systems running multiple
> > workloads, the per-user namespace sysctl max_inotify_instances can be
> > used to further partition inotify instances. However there is no easy
> > way to set a sensible system level max limit on inotify instances and
> > further partition it between the workloads. It is much easier to charge
> > the underlying resource (i.e. memory) behind the inotify instances to
> > the memcg of the workload and let their memory limits limit the number
> > of inotify instances they can create.
>
> Not that I have a problem with this patch, but what problem does it try to
> solve?
I am aiming for the simplicity to not set another limit which can
indirectly be limited by memcg limits. I just want to set the memcg
limit on our production environment which runs multiple workloads on a
system and not think about setting a sensible value to
max_user_instances in production. I would prefer to set
max_user_instances to max int and let the memcg limits of the
workloads limit their inotify usage.
> Are you concerned of users depleting system memory by creating
> userns's and allocating 128 * (struct fsnotify_group) at a time?
>
> IMO, that is not what max_user_instances was meant to protect against.
> There are two reasons I can think of to limit user instances:
> 1. Pre-memgc, user allocation of events is limited to
> <max_user_instances>*<max_queued_events>
> 2. Performance penalty. User can place <max_user_instances>
> watches on the same "hot" directory, that will cause any access to
> that directory by any task on the system to pay the penalty of traversing
> <max_user_instances> marks and attempt to queue <max_user_instances>
> events. That cost, including <max_user_instances> inotify_merge() loops
> could be significant
>
> #1 is not a problem anymore, since you already took care of accounting events
> to the user's memcg.
> #2 is not addressed by your patch.
Yes, I am not addressing #2. Our workloads in prod have their own
private filesystems, so this is not an issue we observed.
>
> >
> > Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > ---
> > fs/notify/group.c | 14 ++++++++++++--
> > fs/notify/inotify/inotify_user.c | 5 +++--
> > include/linux/fsnotify_backend.h | 2 ++
> > 3 files changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/notify/group.c b/fs/notify/group.c
> > index a4a4b1c64d32..fab3cfdb4d9e 100644
> > --- a/fs/notify/group.c
> > +++ b/fs/notify/group.c
> > @@ -114,11 +114,12 @@ EXPORT_SYMBOL_GPL(fsnotify_put_group);
> > /*
> > * Create a new fsnotify_group and hold a reference for the group returned.
> > */
> > -struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
> > +struct fsnotify_group *fsnotify_alloc_group_gfp(const struct fsnotify_ops *ops,
> > + gfp_t gfp)
> > {
> > struct fsnotify_group *group;
> >
> > - group = kzalloc(sizeof(struct fsnotify_group), GFP_KERNEL);
> > + group = kzalloc(sizeof(struct fsnotify_group), gfp);
> > if (!group)
> > return ERR_PTR(-ENOMEM);
> >
> > @@ -139,6 +140,15 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
> >
> > return group;
> > }
> > +EXPORT_SYMBOL_GPL(fsnotify_alloc_group_gfp);
> > +
> > +/*
> > + * Create a new fsnotify_group and hold a reference for the group returned.
> > + */
> > +struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
> > +{
> > + return fsnotify_alloc_group_gfp(ops, GFP_KERNEL);
> > +}
> > EXPORT_SYMBOL_GPL(fsnotify_alloc_group);
> >
> > int fsnotify_fasync(int fd, struct file *file, int on)
> > diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
> > index 59c177011a0f..7cb528c6154c 100644
> > --- a/fs/notify/inotify/inotify_user.c
> > +++ b/fs/notify/inotify/inotify_user.c
> > @@ -632,11 +632,12 @@ static struct fsnotify_group *inotify_new_group(unsigned int max_events)
> > struct fsnotify_group *group;
> > struct inotify_event_info *oevent;
> >
> > - group = fsnotify_alloc_group(&inotify_fsnotify_ops);
> > + group = fsnotify_alloc_group_gfp(&inotify_fsnotify_ops,
> > + GFP_KERNEL_ACCOUNT);
> > if (IS_ERR(group))
> > return group;
> >
> > - oevent = kmalloc(sizeof(struct inotify_event_info), GFP_KERNEL);
> > + oevent = kmalloc(sizeof(struct inotify_event_info), GFP_KERNEL_ACCOUNT);
> > if (unlikely(!oevent)) {
> > fsnotify_destroy_group(group);
> > return ERR_PTR(-ENOMEM);
>
> Any reason why you did not include fanotify in this patch?
The motivation was inotify's max_user_instances but we can charge
fsnotify_group for fanotify as well. Though I would prefer that to be
a separate patch. Let me know what you prefer?
>
> Thanks,
> Amir.
Thanks for the review. I really appreciate your time.
Shakeel
