• Dan Williams's avatar
    mm: introduce MEMORY_DEVICE_FS_DAX and CONFIG_DEV_PAGEMAP_OPS · e7638488
    Dan Williams authored
    In preparation for fixing dax-dma-vs-unmap issues, filesystems need to
    be able to rely on the fact that they will get wakeups on dev_pagemap
    page-idle events. Introduce MEMORY_DEVICE_FS_DAX and
    generic_dax_page_free() as common indicator / infrastructure for dax
    filesytems to require. With this change there are no users of the
    MEMORY_DEVICE_HOST designation, so remove it.
    
    The HMM sub-system extended dev_pagemap to arrange a callback when a
    dev_pagemap managed page is freed. Since a dev_pagemap page is free /
    idle when its reference count is 1 it requires an additional branch to
    check the page-type at put_page() time. Given put_page() is a hot-path
    we do not want to incur that check if HMM is not in use, so a static
    branch is used to avoid that overhead when not necessary.
    
    Now, the FS_DAX implementation wants to reuse this mechanism for
    receiving dev_pagemap ->page_free() callbacks. Rework the HMM-specific
    static-key into a generic mechanism that either HMM or FS_DAX code paths
    can enable.
    
    For ARCH=um builds, and any other arch that lacks ZONE_DEVICE support,
    care must be taken to compile out the DEV_PAGEMAP_OPS infrastructure.
    However, we still need to support FS_DAX in the FS_DAX_LIMITED case
    implemented by the s390/dcssblk driver.
    
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Michal Hocko <mhocko@suse.com>
    Reported-by: 's avatarkbuild test robot <lkp@intel.com>
    Reported-by: 's avatarThomas Meyer <thomas@m3y3r.de>
    Reported-by: 's avatarDave Jiang <dave.jiang@intel.com>
    Cc: "Jérôme Glisse" <jglisse@redhat.com>
    Reviewed-by: 's avatarJan Kara <jack@suse.cz>
    Reviewed-by: 's avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: 's avatarDan Williams <dan.j.williams@intel.com>
    e7638488