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    SubjectRe: [PATCH 0/6 v5.1] cfq-iosched: Introduce CFQ group hierarchical scheduling and "use_hierarchy" interface
    On Wed, Feb 23, 2011 at 11:01:35AM +0800, Gui Jianfeng wrote:
    > Hi
    >
    > I rebase this series on top of *for-next* branch, it will make merging life easier.
    >
    > Previously, I posted a patchset to add support of CFQ group hierarchical scheduling
    > in the way that it puts all CFQ queues in a hidden group and schedules with other
    > CFQ group under their parent. The patchset is available here,
    > http://lkml.org/lkml/2010/8/30/30

    Gui,

    I was running some tests (iostest) with these patches and my system crashed
    after a while.

    To be precise I was running "brrmmap" test of iostest.

    train.lab.bos.redhat.com login: [72194.404201] EXT4-fs (dm-1): mounted
    filesystem with ordered data mode. Opts: (null)
    [72642.818976] EXT4-fs (dm-1): mounted filesystem with ordered data mode.
    Opts: (null)
    [72931.409460] BUG: unable to handle kernel NULL pointer dereference at
    0000000000000010
    [72931.410216] IP: [<ffffffff812265ff>] __rb_rotate_left+0xb/0x64
    [72931.410216] PGD 134d80067 PUD 12f524067 PMD 0
    [72931.410216] Oops: 0000 [#1] SMP
    [72931.410216] last sysfs file:
    /sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size
    [72931.410216] CPU 3
    [72931.410216] Modules linked in: kvm_intel kvm qla2xxx scsi_transport_fc
    [last unloaded: scsi_wait_scan]
    [72931.410216]
    [72931.410216] Pid: 18675, comm: sh Not tainted 2.6.38-rc4+ #3 0A98h/HP
    xw8600 Workstation
    [72931.410216] RIP: 0010:[<ffffffff812265ff>] [<ffffffff812265ff>]
    __rb_rotate_left+0xb/0x64
    [72931.410216] RSP: 0000:ffff88012f461480 EFLAGS: 00010086
    [72931.410216] RAX: 0000000000000000 RBX: ffff880135f40c00 RCX:
    ffffffffffffdcc8
    [72931.410216] RDX: ffff880135f43800 RSI: ffff880135f43000 RDI:
    ffff880135f42c00
    [72931.410216] RBP: ffff88012f461480 R08: ffff880135f40c00 R09:
    ffff880135f43018
    [72931.410216] R10: 0000000000000000 R11: 0000001000000000 R12:
    ffff880135f42c00
    [72931.410216] R13: ffff880135f41808 R14: ffff880135f43000 R15:
    ffff880135f40c00
    [72931.410216] FS: 0000000000000000(0000) GS:ffff8800bfcc0000(0000)
    knlGS:0000000000000000
    [72931.410216] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    [72931.410216] CR2: 0000000000000010 CR3: 000000013774f000 CR4:
    00000000000006e0
    [72931.410216] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
    0000000000000000
    [72931.410216] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
    0000000000000400
    [72931.410216] Process sh (pid: 18675, threadinfo ffff88012f460000, task
    ffff8801376e6f90)
    [72931.410216] Stack:
    [72931.410216] ffff88012f4614b8 ffffffff81226778 ffff880135f43000
    ffff880135f43000
    [72931.410216] ffff88011c5bed00 0000000000000000 0000000000000001
    ffff88012f4614d8
    [72931.410216] ffffffff8121c521 0000001000000000 ffff880135f41800
    ffff88012f461528
    [72931.410216] Call Trace:
    [72931.410216] [<ffffffff81226778>] rb_insert_color+0xbc/0xe5
    [72931.410216] [<ffffffff8121c521>]
    __cfq_entity_service_tree_add+0x76/0xa5
    [72931.410216] [<ffffffff8121cb28>] cfq_service_tree_add+0x383/0x3eb
    [72931.410216] [<ffffffff8121cbaa>] cfq_resort_rr_list+0x1a/0x2a
    [72931.410216] [<ffffffff8121eb06>] cfq_add_rq_rb+0xbd/0xff
    [72931.410216] [<ffffffff8121ec0a>] cfq_insert_request+0xc2/0x556
    [72931.410216] [<ffffffff8120a44c>] elv_insert+0x118/0x188
    [72931.410216] [<ffffffff8120a52a>] __elv_add_request+0x6e/0x75
    [72931.410216] [<ffffffff812102d0>] __make_request+0x3ac/0x42f
    [72931.410216] [<ffffffff8120e9ca>] generic_make_request+0x2ec/0x356
    [72931.410216] [<ffffffff8120eb05>] submit_bio+0xd1/0xdc
    [72931.410216] [<ffffffff8110bea3>] submit_bh+0xe6/0x108
    [72931.410216] [<ffffffff8110eb9d>] __bread+0x4c/0x6f
    [72931.410216] [<ffffffff811453ab>] ext3_get_branch+0x64/0xdf
    [72931.410216] [<ffffffff81146f5c>] ext3_get_blocks_handle+0x9b/0x90b
    [72931.410216] [<ffffffff81147882>] ext3_get_block+0xb6/0xf6
    [72931.410216] [<ffffffff81113520>] do_mpage_readpage+0x198/0x4bd
    [72931.410216] [<ffffffff810c01b2>] ? __inc_zone_page_state+0x29/0x2b
    [72931.410216] [<ffffffff810ab6e4>] ? add_to_page_cache_locked+0xb6/0x10d
    [72931.410216] [<ffffffff81113980>] mpage_readpages+0xd6/0x123
    [72931.410216] [<ffffffff811477cc>] ? ext3_get_block+0x0/0xf6
    [72931.410216] [<ffffffff811477cc>] ? ext3_get_block+0x0/0xf6
    [72931.410216] [<ffffffff810da750>] ? alloc_pages_current+0xa2/0xc5
    [72931.410216] [<ffffffff81145a6a>] ext3_readpages+0x18/0x1a
    [72931.410216] [<ffffffff810b31fc>] __do_page_cache_readahead+0x111/0x1a7
    [72931.410216] [<ffffffff810b32ae>] ra_submit+0x1c/0x20
    [72931.410216] [<ffffffff810acb1b>] filemap_fault+0x165/0x35b
    [72931.410216] [<ffffffff810c6ce1>] __do_fault+0x50/0x3e2
    [72931.410216] [<ffffffff810c7cf8>] handle_pte_fault+0x2ff/0x779
    [72931.410216] [<ffffffff810b05c9>] ? __free_pages+0x1b/0x24
    [72931.410216] [<ffffffff810c82d1>] handle_mm_fault+0x15f/0x173
    [72931.410216] [<ffffffff815b0963>] do_page_fault+0x348/0x36a
    [72931.410216] [<ffffffff810f21c5>] ? path_put+0x1d/0x21
    [72931.410216] [<ffffffff810f21c5>] ? path_put+0x1d/0x21
    [72931.410216] [<ffffffff815adf1f>] page_fault+0x1f/0x30
    [72931.410216] Code: 48 83 c4 18 44 89 e8 5b 41 5c 41 5d c9 c3 48 83 7b 18
    00 0f 84 71 ff ff ff e9 77 ff ff ff 90 90 48 8b 47 08 55 48 8b 17 48 89 e5
    <48> 8b 48 10 48 83 e2 fc 48 85 c9 48 89 4f 08 74 10 4c 8b 40 10
    [72931.410216] RIP [<ffffffff812265ff>] __rb_rotate_left+0xb/0x64
    [72931.410216] RSP <ffff88012f461480>
    [72931.410216] CR2: 0000000000000010
    [72931.410216] ---[ end trace cddc7a4456407f6a ]---

    Thanks
    Vivek

    >
    > Vivek think this approach isn't so instinct that we should treat CFQ queues
    > and groups at the same level. Here is the new approach for hierarchical
    > scheduling based on Vivek's suggestion. The most big change of CFQ is that
    > it gets rid of cfq_slice_offset logic, and makes use of vdisktime for CFQ
    > queue scheduling just like CFQ group does. But I still give cfqq some jump
    > in vdisktime based on ioprio, thanks for Vivek to point out this. Now CFQ
    > queue and CFQ group use the same scheduling algorithm.
    >
    > "use_hierarchy" interface is now added to switch between hierarchical mode
    > and flat mode. It works as memcg.
    >
    > V4 -> V5 Changes:
    > - Change boosting base to a smaller value.
    > - Rename repostion_time to position_time
    > - Replace duplicated code by calling cfq_scale_slice()
    > - Remove redundant use_hierarchy in cfqd
    > - Fix grp_service_tree comment
    > - Rename init_cfqe() to init_group_cfqe()
    >
    > --
    > V3 -> V4 Changes:
    > - Take io class into account when calculating the boost value.
    > - Refine the vtime boosting logic as Vivek's Suggestion.
    > - Make the calculation of group slice cross all service trees under a group.
    > - Modify Documentation in terms of Vivek's comments.
    >
    > --
    > V2 -> V3 Changes:
    > - Starting from cfqd->grp_service_tree for both hierarchical mode and flat mode
    > - Avoid recursion when allocating cfqg and force dispatch logic
    > - Fix a bug when boosting vdisktime
    > - Adjusting total_weight accordingly when changing weight
    > - Change group slice calculation into a hierarchical way
    > - Keep flat mode rather than deleting it first then adding it later
    > - kfree the parent cfqg if there nobody references to it
    > - Simplify select_queue logic by using some wrap function
    > - Make "use_hierarchy" interface work as memcg
    > - Make use of time_before() for vdisktime compare
    > - Update Document
    > - Fix some code style problems
    >
    > --
    > V1 -> V2 Changes:
    > - Raname "struct io_sched_entity" to "struct cfq_entity" and don't differentiate
    > queue_entity and group_entity, just use cfqe instead.
    > - Give newly added cfqq a small vdisktime jump accord to its ioprio.
    > - Make flat mode as default CFQ group scheduling mode.
    > - Introduce "use_hierarchy" interface.
    > - Update blkio cgroup documents
    >
    > Documentation/cgroups/blkio-controller.txt | 81 +-
    > block/blk-cgroup.c | 61 +
    > block/blk-cgroup.h | 3
    > block/cfq-iosched.c | 959 ++++++++++++++++++++---------
    > 4 files changed, 815 insertions(+), 289 deletions(-)
    >
    > Thanks,
    > Gui


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