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

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Date:   Fri, 15 Oct 2021 09:19:48 +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 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.

Thanks,
Amir.