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    Subject[PATCHSET cgroup/for-3.15] cgroup: convert to kernfs
    Date
    Hello,

    cgroup filesystem code was derived from the original sysfs
    implementation which was heavily intertwined with vfs objects and
    locking with the goal of re-using the existing vfs infrastructure.
    That experiment turned out rather disastrous and sysfs switched, a
    long time ago, to distributed filesystem model where a separate
    representation is maintained which is queried by vfs. Unfortunately,
    cgroup stuck with the failed experiment all these years and
    accumulated even more problems over time.

    Locking and object lifetime management being entangled with vfs is
    probably the most egregious. vfs was never designed to be misused
    like this and cgroup ends up jumping through various convoluted
    dancing to make things work. Even then, operations across multiple
    cgroups can't be done safely as it'll deadlock with rename locking.

    Recently, kernfs is separated out from sysfs so that it can be used by
    users other than sysfs. This patchset converts cgroup to use kernfs.
    This simplifies code base quite a bit and allows further cleanups and
    implementation of features which depend on operating across multiple
    nodes.

    This patchset contains the following 13 patches.

    0001-cgroup-improve-css_from_dir-into-css_tryget_from_dir.patch
    0002-cgroup-introduce-cgroup_tree_mutex.patch
    0003-cgroup-release-cgroup_mutex-over-file-removals.patch
    0004-cgroup-restructure-locking-and-error-handling-in-cgr.patch
    0005-cgroup-factor-out-cgroup_setup_root-from-cgroup_moun.patch
    0006-cgroup-update-cgroup-name-handling.patch
    0007-cgroup-make-cgroup_subsys-base_cftypes-use-cgroup_ad.patch
    0008-cgroup-update-the-meaning-of-cftype-max_write_len.patch
    0009-cgroup-introduce-cgroup_init-exit_cftypes.patch
    0010-cgroup-introduce-cgroup_ino.patch
    0011-cgroup-misc-preps-for-kernfs-conversion.patch
    0012-cgroup-relocate-functions-in-preparation-of-kernfs-c.patch
    0013-cgroup-convert-to-kernfs.patch

    0001 updates css_from_dir() into css_tryget_from_dir() so that the
    caller doesn't have to worry about RCU locking.

    0002-0004 introduce cgroup_tree_mutex and prepare locking.

    0005-0006 are misc preps.

    0007-0008 update cftype handling in preparation.

    0009-0012 are misc preps.

    0013 converts cgroup to kernfs.

    This patchset is on top of

    linus#master 54c0a4b46150 ("Merge branch 'akpm' (incoming from Andrew)")
    + [1] [PATCHSET cgroup/for-3.14-fixes] cgroup: four misc fixes
    + [2] [PATCH] arm, pm, vmpressure: add missing slab.h includes
    + [3] [PATCHSET v2 cgroup/for-3.15] cgroup: drop module support and cgroup_root_mutex
    + git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git review-kernfs-cgroup-prep

    and also available in the following git branch.

    git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-kernfs-conversion

    diffstat follows.

    block/blk-throttle.c | 4
    block/cfq-iosched.c | 3
    include/linux/cgroup.h | 71 --
    kernel/cgroup.c | 1712 ++++++++++++++++++++-----------------------------
    kernel/events/core.c | 17
    mm/memcontrol.c | 16
    mm/memory-failure.c | 8
    7 files changed, 754 insertions(+), 1077 deletions(-)

    Thanks.

    --
    tejun

    [L] http://lkml.kernel.org/g/<1389982317-22225-1-git-send-email-tj@kernel.org>
    [1] http://lkml.kernel.org/g/<1390923125-4369-1-git-send-email-tj@kernel.org>
    [2] http://lkml.kernel.org/g/<20140128221922.GC16060@mtj.dyndns.org>
    [3] http://lkml.kernel.org/g/<1390952641-15950-1-git-send-email-tj@kernel.org>


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