| 1 | ==========================
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| 2 | Shrinker Debugfs Interface
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| 3 | ==========================
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| 4 |
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| 5 | Shrinker debugfs interface provides a visibility into the kernel memory
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| 6 | shrinkers subsystem and allows to get information about individual shrinkers
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| 7 | and interact with them.
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| 8 |
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| 9 | For each shrinker registered in the system a directory in **<debugfs>/shrinker/**
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| 10 | is created. The directory's name is composed from the shrinker's name and an
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| 11 | unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*.
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| 12 |
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| 13 | Each shrinker directory contains **count** and **scan** files, which allow to
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| 14 | trigger *count_objects()* and *scan_objects()* callbacks for each memcg and
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| 15 | numa node (if applicable).
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| 16 |
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| 17 | Usage:
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| 18 | ------
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| 19 |
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| 20 | 1. *List registered shrinkers*
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| 21 |
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| 22 | ::
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| 23 |
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| 24 | $ cd /sys/kernel/debug/shrinker/
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| 25 | $ ls
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| 26 | dquota-cache-16 sb-devpts-28 sb-proc-47 sb-tmpfs-42
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| 27 | mm-shadow-18 sb-devtmpfs-5 sb-proc-48 sb-tmpfs-43
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| 28 | mm-zspool:zram0-34 sb-hugetlbfs-17 sb-pstore-31 sb-tmpfs-44
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| 29 | rcu-kfree-0 sb-hugetlbfs-33 sb-rootfs-2 sb-tmpfs-49
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| 30 | sb-aio-20 sb-iomem-12 sb-securityfs-6 sb-tracefs-13
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| 31 | sb-anon_inodefs-15 sb-mqueue-21 sb-selinuxfs-22 sb-xfs:vda1-36
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| 32 | sb-bdev-3 sb-nsfs-4 sb-sockfs-8 sb-zsmalloc-19
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| 33 | sb-bpf-32 sb-pipefs-14 sb-sysfs-26 thp-deferred_split-10
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| 34 | sb-btrfs:vda2-24 sb-proc-25 sb-tmpfs-1 thp-zero-9
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| 35 | sb-cgroup2-30 sb-proc-39 sb-tmpfs-27 xfs-buf:vda1-37
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| 36 | sb-configfs-23 sb-proc-41 sb-tmpfs-29 xfs-inodegc:vda1-38
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| 37 | sb-dax-11 sb-proc-45 sb-tmpfs-35
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| 38 | sb-debugfs-7 sb-proc-46 sb-tmpfs-40
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| 39 |
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| 40 | 2. *Get information about a specific shrinker*
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| 41 |
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| 42 | ::
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| 43 |
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| 44 | $ cd sb-btrfs\:vda2-24/
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| 45 | $ ls
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| 46 | count scan
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| 47 |
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| 48 | 3. *Count objects*
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| 49 |
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| 50 | Each line in the output has the following format::
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| 51 |
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| 52 | <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
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| 53 | <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
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| 54 | ...
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| 55 |
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| 56 | If there are no objects on all numa nodes, a line is omitted. If there
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| 57 | are no objects at all, the output might be empty.
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| 58 |
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| 59 | If the shrinker is not memcg-aware or CONFIG_MEMCG is off, 0 is printed
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| 60 | as cgroup inode id. If the shrinker is not numa-aware, 0's are printed
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| 61 | for all nodes except the first one.
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| 62 | ::
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| 63 |
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| 64 | $ cat count
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| 65 | 1 224 2
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| 66 | 21 98 0
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| 67 | 55 818 10
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| 68 | 2367 2 0
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| 69 | 2401 30 0
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| 70 | 225 13 0
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| 71 | 599 35 0
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| 72 | 939 124 0
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| 73 | 1041 3 0
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| 74 | 1075 1 0
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| 75 | 1109 1 0
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| 76 | 1279 60 0
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| 77 | 1313 7 0
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| 78 | 1347 39 0
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| 79 | 1381 3 0
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| 80 | 1449 14 0
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| 81 | 1483 63 0
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| 82 | 1517 53 0
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| 83 | 1551 6 0
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| 84 | 1585 1 0
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| 85 | 1619 6 0
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| 86 | 1653 40 0
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| 87 | 1687 11 0
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| 88 | 1721 8 0
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| 89 | 1755 4 0
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| 90 | 1789 52 0
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| 91 | 1823 888 0
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| 92 | 1857 1 0
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| 93 | 1925 2 0
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| 94 | 1959 32 0
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| 95 | 2027 22 0
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| 96 | 2061 9 0
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| 97 | 2469 799 0
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| 98 | 2537 861 0
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| 99 | 2639 1 0
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| 100 | 2707 70 0
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| 101 | 2775 4 0
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| 102 | 2877 84 0
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| 103 | 293 1 0
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| 104 | 735 8 0
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| 105 |
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| 106 | 4. *Scan objects*
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| 107 |
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| 108 | The expected input format::
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| 109 |
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| 110 | <cgroup inode id> <numa id> <number of objects to scan>
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| 111 |
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| 112 | For a non-memcg-aware shrinker or on a system with no memory
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| 113 | cgrups **0** should be passed as cgroup id.
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| 114 | ::
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| 115 |
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| 116 | $ cd /sys/kernel/debug/shrinker/
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| 117 | $ cd sb-btrfs\:vda2-24/
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| 118 |
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| 119 | $ cat count | head -n 5
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| 120 | 1 212 0
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| 121 | 21 97 0
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| 122 | 55 802 5
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| 123 | 2367 2 0
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| 124 | 225 13 0
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| 125 |
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| 126 | $ echo "55 0 200" > scan
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| 127 |
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| 128 | $ cat count | head -n 5
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| 129 | 1 212 0
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| 130 | 21 96 0
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| 131 | 55 752 5
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| 132 | 2367 2 0
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| 133 | 225 13 0
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