linux-ext4 - Re: [PATCH v7 18/28] fanotify: Pre-allocate pool of error events

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Date:   Fri, 15 Oct 2021 10:33:50 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Jan Kara <jack@...e.com>, "Darrick J. Wong" <djwong@...nel.org>,
        Theodore Tso <tytso@....edu>,
        David Howells <dhowells@...hat.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Matthew Bobrowski <repnop@...gle.com>, kernel@...labora.com
Subject: Re: [PATCH v7 18/28] fanotify: Pre-allocate pool of error events

On Fri, Oct 15, 2021 at 9:19 AM Amir Goldstein <amir73il@...il.com> wrote:
>
> On Fri, Oct 15, 2021 at 12:39 AM Gabriel Krisman Bertazi
> <krisman@...labora.com> wrote:
> >
> > Error reporting needs to be done in an atomic context.  This patch
> > introduces a group-wide mempool of error events, shared by all
> > marks in this group.
> >
> > Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
> > ---
> >  fs/notify/fanotify/fanotify.c      |  3 +++
> >  fs/notify/fanotify/fanotify.h      | 11 +++++++++++
> >  fs/notify/fanotify/fanotify_user.c | 26 +++++++++++++++++++++++++-
> >  include/linux/fsnotify_backend.h   |  2 ++
> >  4 files changed, 41 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> > index 8f152445d75c..01d68dfc74aa 100644
> > --- a/fs/notify/fanotify/fanotify.c
> > +++ b/fs/notify/fanotify/fanotify.c
> > @@ -819,6 +819,9 @@ static void fanotify_free_group_priv(struct fsnotify_group *group)
> >         if (group->fanotify_data.ucounts)
> >                 dec_ucount(group->fanotify_data.ucounts,
> >                            UCOUNT_FANOTIFY_GROUPS);
> > +
> > +       if (mempool_initialized(&group->fanotify_data.error_events_pool))
> > +               mempool_exit(&group->fanotify_data.error_events_pool);
> >  }
> >
> >  static void fanotify_free_path_event(struct fanotify_event *event)
> > diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
> > index c42cf8fd7d79..a577e87fac2b 100644
> > --- a/fs/notify/fanotify/fanotify.h
> > +++ b/fs/notify/fanotify/fanotify.h
> > @@ -141,6 +141,7 @@ enum fanotify_event_type {
> >         FANOTIFY_EVENT_TYPE_PATH,
> >         FANOTIFY_EVENT_TYPE_PATH_PERM,
> >         FANOTIFY_EVENT_TYPE_OVERFLOW, /* struct fanotify_event */
> > +       FANOTIFY_EVENT_TYPE_FS_ERROR, /* struct fanotify_error_event */
> >         __FANOTIFY_EVENT_TYPE_NUM
> >  };
> >
> > @@ -196,6 +197,16 @@ FANOTIFY_NE(struct fanotify_event *event)
> >         return container_of(event, struct fanotify_name_event, fae);
> >  }
> >
> > +struct fanotify_error_event {
> > +       struct fanotify_event fae;
> > +};
> > +
> > +static inline struct fanotify_error_event *
> > +FANOTIFY_EE(struct fanotify_event *event)
> > +{
> > +       return container_of(event, struct fanotify_error_event, fae);
> > +}
> > +
> >  static inline __kernel_fsid_t *fanotify_event_fsid(struct fanotify_event *event)
> >  {
> >         if (event->type == FANOTIFY_EVENT_TYPE_FID)
> > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> > index 66ee3c2805c7..f1cf863d6f9f 100644
> > --- a/fs/notify/fanotify/fanotify_user.c
> > +++ b/fs/notify/fanotify/fanotify_user.c
> > @@ -30,6 +30,7 @@
> >  #define FANOTIFY_DEFAULT_MAX_EVENTS    16384
> >  #define FANOTIFY_OLD_DEFAULT_MAX_MARKS 8192
> >  #define FANOTIFY_DEFAULT_MAX_GROUPS    128
> > +#define FANOTIFY_DEFAULT_FEE_POOL      32
> >
>
> We can probably start with a more generous pool (128?)
> It doesn't cost that much.
> But anyway, I think this pool needs to auto-grow (up to a maximum size)
> instead of having a rigid arbitrary limit.
>

As long as the pool grows, I don't mind if it start at size 32,
but I just noticed that mempools cannot be accounted to memcg??
Then surely the maximum size need to be kept pretty low.

Thanks,
Amir.