• Miklos Szeredi's avatar
    fuse: separate queue for FORGET requests · 07e77dca
    Miklos Szeredi authored
    
    
    Terje Malmedal reports that a fuse filesystem with 32 million inodes
    on a machine with lots of memory can go unresponsive for up to 30
    minutes when all those inodes are evicted from the icache.
    
    The reason is that FORGET messages, sent when the inode is evicted,
    are queued up together with regular filesystem requests, and while the
    huge queue of FORGET messages are processed no other filesystem
    operation can proceed.
    
    Since a full fuse request structure is allocated for each inode, these
    take up quite a bit of memory as well.
    
    To solve these issues, create a slim 'fuse_forget_link' structure
    containing just the minimum of information required to send the FORGET
    request and chain these on a separate queue.
    
    When userspace is asking for a request make sure that FORGET and
    non-FORGET requests are selected fairly: for each 8 non-FORGET allow
    16 FORGET requests.  This will make sure FORGETs do not pile up, yet
    other requests are also allowed to proceed while the queued FORGETs
    are processed.
    Reported-by: default avatarTerje Malmedal <terje.malmedal@usit.uio.no>
    Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
    07e77dca