• Jan Kara's avatar
    fsnotify: do not share events between notification groups · 7053aee2
    Jan Kara authored
    Currently fsnotify framework creates one event structure for each
    notification event and links this event into all interested notification
    groups.  This is done so that we save memory when several notification
    groups are interested in the event.  However the need for event
    structure shared between inotify & fanotify bloats the event structure
    so the result is often higher memory consumption.
    Another problem is that fsnotify framework keeps path references with
    outstanding events so that fanotify can return open file descriptors
    with its events.  This has the undesirable effect that filesystem cannot
    be unmounted while there are outstanding events - a regression for
    inotify compared to a situation before it was converted to fsnotify
    framework.  For fanotify this problem is hard to avoid and users of
    fanotify should kind of expect this behavior when they ask for file
    descriptors from notified files.
    This patch changes fsnotify and its users to create separate event
    structure for each group.  This allows for much simpler code (~400 lines
    removed by this patch) and also smaller event structures.  For example
    on 64-bit system original struct fsnotify_event consumes 120 bytes, plus
    additional space for file name, additional 24 bytes for second and each
    subsequent group linking the event, and additional 32 bytes for each
    inotify group for private data.  After the conversion inotify event
    consumes 48 bytes plus space for file name which is considerably less
    memory unless file names are long and there are several groups
    interested in the events (both of which are uncommon).  Fanotify event
    fits in 56 bytes after the conversion (fanotify doesn't care about file
    names so its events don't have to have it allocated).  A win unless
    there are four or more fanotify groups interested in the event.
    The conversion also solves the problem with unmount when only inotify is
    used as we don't have to grab path references for inotify events.
    [hughd@google.com: fanotify: fix corruption preventing startup]
    Signed-off-by: default avatarJan Kara <jack@suse.cz>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Cc: Eric Paris <eparis@parisplace.org>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
notification.c 5.92 KB