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Yafang Shao says:
====================
Currently we can't get bpf memory usage reliably either from memcg or
from bpftool.
In memcg, there's not a 'bpf' item in memory.stat, but only 'kernel',
'sock', 'vmalloc' and 'percpu' which may related to bpf memory. With
these items we still can't get the bpf memory usage, because bpf memory
usage may far less than the kmem in a memcg, for example, the dentry may
consume lots of kmem.
bpftool now shows the bpf memory footprint, which is difference with bpf
memory usage. The difference can be quite great in some cases, for example,
- non-preallocated bpf map
The non-preallocated bpf map memory usage is dynamically changed. The
allocated elements count can be from 0 to the max entries. But the
memory footprint in bpftool only shows a fixed number.
- bpf metadata consumes more memory than bpf element
In some corner cases, the bpf metadata can consumes a lot more memory
than bpf element consumes. For example, it can happen when the element
size is quite small.
- some maps don't have key, value or max_entries
For example the key_size and value_size of ringbuf is 0, so its
memlock is always 0.
We need a way to show the bpf memory usage especially there will be more
and more bpf programs running on the production environment and thus the
bpf memory usage is not trivial.
This patchset introduces a new map ops ->map_mem_usage to calculate the
memory usage. Note that we don't intend to make the memory usage 100%
accurate, while our goal is to make sure there is only a small difference
between what bpftool reports and the real memory. That small difference
can be ignored compared to the total usage. That is enough to monitor
the bpf memory usage. For example, the user can rely on this value to
monitor the trend of bpf memory usage, compare the difference in bpf
memory usage between different bpf program versions, figure out which
maps consume large memory, and etc.
This patchset implements the bpf memory usage for all maps, and yet there's
still work to do. We don't want to introduce runtime overhead in the
element update and delete path, but we have to do it for some
non-preallocated maps,
- devmap, xskmap
When we update or delete an element, it will allocate or free memory.
In order to track this dynamic memory, we have to track the count in
element update and delete path.
- cpumap
The element size of each cpumap element is not determinated. If we
want to track the usage, we have to count the size of all elements in
the element update and delete path. So I just put it aside currently.
- local_storage, bpf_local_storage
When we attach or detach a cgroup, it will allocate or free memory. If
we want to track the dynamic memory, we also need to do something in
the update and delete path. So I just put it aside currently.
- offload map
The element update and delete of offload map is via the netdev dev_ops,
in which it may dynamically allocate or free memory, but this dynamic
memory isn't counted in offload map memory usage currently.
The result of each map can be found in the individual patch.
We may also need to track per-container bpf memory usage, that will be
addressed by a different patchset.
Changes:
v3->v4: code improvement on ringbuf (Andrii)
use READ_ONCE() to read lpm_trie (Tao)
explain why we can't get bpf memory usage from memcg.
v2->v3: check callback at map creation time and avoid warning (Alexei)
fix build error under CONFIG_BPF=n (lkp@intel.com)
v1->v2: calculate the memory usage within bpf (Alexei)
- [v1] bpf, mm: bpf memory usage
https://lwn.net/Articles/921991/
- [RFC PATCH v2] mm, bpf: Add BPF into /proc/meminfo
https://lwn.net/Articles/919848/
- [RFC PATCH v1] mm, bpf: Add BPF into /proc/meminfo
https://lwn.net/Articles/917647/
- [RFC PATCH] bpf, mm: Add a new item bpf into memory.stat
https://lore.kernel.org/bpf/20220921170002.29557-1-laoar.shao@gmail].com/
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.