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    Subject[PATCH 00/11] Swap-over-NFS without deadlocking V3
    Changelog since V2
    o Nothing significant, just rebases. A radix tree lookup is replaced with
    a linear search would be the biggest rebase artifact

    This patch series is based on top of "Swap-over-NBD without deadlocking v9"
    as it depends on the same reservation of PF_MEMALLOC reserves logic.

    When a user or administrator requires swap for their application, they
    create a swap partition and file, format it with mkswap and activate it with
    swapon. In diskless systems this is not an option so if swap if required
    then swapping over the network is considered. The two likely scenarios
    are when blade servers are used as part of a cluster where the form factor
    or maintenance costs do not allow the use of disks and thin clients.

    The Linux Terminal Server Project recommends the use of the Network
    Block Device (NBD) for swap but this is not always an option. There is
    no guarantee that the network attached storage (NAS) device is running
    Linux or supports NBD. However, it is likely that it supports NFS so there
    are users that want support for swapping over NFS despite any performance
    concern. Some distributions currently carry patches that support swapping
    over NFS but it would be preferable to support it in the mainline kernel.

    Patch 1 avoids a stream-specific deadlock that potentially affects TCP.

    Patch 2 is a small modification to SELinux to avoid using PFMEMALLOC

    Patch 3 adds three helpers for filesystems to handle swap cache pages.
    For example, page_file_mapping() returns page->mapping for
    file-backed pages and the address_space of the underlying
    swap file for swap cache pages.

    Patch 4 adds two address_space_operations to allow a filesystem
    to pin all metadata relevant to a swapfile in memory. Upon
    successful activation, the swapfile is marked SWP_FILE and
    the address space operation ->direct_IO is used for writing
    and ->readpage for reading in swap pages.

    Patch 5 notes that patch 3 is bolting
    filesystem-specific-swapfile-support onto the side and that
    the default handlers have different information to what
    is available to the filesystem. This patch refactors the
    code so that there are generic handlers for each of the new
    address_space operations.

    Patch 6 adds an API to allow a vector of kernel addresses to be
    translated to struct pages and pinned for IO.

    Patch 7 updates NFS to use the helpers from patch 3 where necessary.

    Patch 8 avoids setting PF_private on PG_swapcache pages within NFS.

    Patch 9 implements the new swapfile-related address_space operations
    for NFS and teaches the direct IO handler how to manage
    kernel addresses.

    Patch 10 prevents page allocator recursions in NFS by using GFP_NOIO
    where appropriate.

    Patch 11 fixes a NULL pointer dereference that occurs when using

    With the patches applied, it is possible to mount a swapfile that is on an
    NFS filesystem. Swap performance is not great with a swap stress test taking
    roughly twice as long to complete than if the swap device was backed by NBD.

    Documentation/filesystems/Locking | 13 ++++
    Documentation/filesystems/vfs.txt | 12 ++++
    fs/nfs/Kconfig | 8 +++
    fs/nfs/direct.c | 94 ++++++++++++++++--------
    fs/nfs/file.c | 28 ++++++--
    fs/nfs/inode.c | 6 ++
    fs/nfs/internal.h | 7 +-
    fs/nfs/pagelist.c | 6 +-
    fs/nfs/read.c | 6 +-
    fs/nfs/write.c | 98 +++++++++++++++----------
    include/linux/blk_types.h | 2 +
    include/linux/fs.h | 9 +++
    include/linux/mm.h | 29 ++++++++
    include/linux/nfs_fs.h | 4 +-
    include/linux/pagemap.h | 5 ++
    include/linux/sunrpc/xprt.h | 3 +
    include/linux/swap.h | 8 +++
    include/net/sock.h | 7 +-
    mm/memory.c | 53 ++++++++++++++
    mm/page_io.c | 144 +++++++++++++++++++++++++++++++++++++
    mm/swap_state.c | 2 +-
    mm/swapfile.c | 141 ++++++++++++++----------------------
    net/caif/caif_socket.c | 2 +-
    net/core/sock.c | 2 +-
    net/ipv4/tcp_input.c | 12 ++--
    net/sctp/ulpevent.c | 2 +-
    net/sunrpc/Kconfig | 5 ++
    net/sunrpc/clnt.c | 2 +
    net/sunrpc/sched.c | 7 +-
    net/sunrpc/xprtsock.c | 53 ++++++++++++++
    security/selinux/avc.c | 2 +-
    31 files changed, 585 insertions(+), 187 deletions(-)


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