new: configure syscall buffer dimension from Falco

[Andreagit97]

What type of PR is this?

/kind feature

Any specific area of the project related to this PR?

What this PR does / why we need it:

As discussed in various places (#2164 (comment), #2164 (comment), #2208) this PR adds the possibility to change the syscall buffer dimension through the Falco configuration file.

The approach used is the one described here #2208 (comment). Users will have an array of indexes that map to precise buffer dimensions in bytes. You can find more information in the falco.yaml file, but just for simplicity I report them here:

# --- [Description]
#
# This is an index that controls the dimension of the syscall buffers.
# The syscall buffer is the shared space between Falco and its drivers where all the syscall events
# are stored.
# Falco uses a syscall buffer for every online CPU, and all these buffers share the same dimension.
# So this parameter allows you to control the size of all the buffers!
#
# --- [Usage]
#
# You can choose between different indexes: from `1` to `10` (`0` is reserved for future uses).
# Every index corresponds to a dimension in bytes:
#
# [(*), 1 MB, 2 MB, 4 MB, 8 MB, 16 MB, 32 MB, 64 MB, 128 MB, 256 MB, 512 MB]
#   ^    ^     ^     ^     ^     ^      ^      ^       ^       ^       ^
#   |    |     |     |     |     |      |      |       |       |       |
#   0    1     2     3     4     5      6      7       8       9       10
#
# As you can see the `0` index is reserved, while the index `1` corresponds to
# `1 MB` and so on.
#
# These dimensions in bytes derive from the fact that the buffer size must be:
# (1) a power of 2.
# (2) a multiple of your system_page_dimension.
# (3) greater than `2 * (system_page_dimension)`.
#
# According to these constraints is possible that sometimes you cannot use all the indexes, let's consider an
# example to better understand it:
# If you have a `page_size` of 1 MB the first available buffer size is 4 MB because 2 MB is exactly
# `2 * (system_page_size)` -> `2 * 1 MB`, but this is not enough we need more than `2 * (system_page_size)`!
# So from this example is clear that if you have a page size of 1 MB the first index that you can use is `3`.
#
# Please note: this is a very extreme case just to let you understand the mechanism, usually the page size is something
# like 4 KB so you have no problem at all and you can use all the indexes (from `1` to `10`).
#
# To check your system page size use the Falco `--page-size` command line option. The output on a system with a page
# size of 4096 Bytes (4 KB) should be the following:
#
# "Your system page size is: 4096 bytes."
#
# --- [Suggestions]
#
# Before the introduction of this param the buffer size was fixed to 8 MB (so index `4`, as you can see
# in the default value below).
# You can increase the buffer size when you face syscall drops. A size of 16 MB (so index `5`) can reduce
# syscall drops in production-heavy systems without noticeable impact. Very large buffers however could
# slow down the entire machine.
# On the other side you can try to reduce the buffer size to speed up the system, but this could
# increase the number of syscall drops!
# As a final remark consider that the buffer size is mapped twice in the process' virtual memory so a buffer of 8 MB
# will result in a 16 MB area in the process virtual memory.
# Please pay attention when you use this parameter and change it only if the default size doesn't fit your use case.

syscall_buf_size_preset: 4

I added also a new command line option --page-size to let the user easily obtain the page size of their system

If you have any suggestions I'm all ears :)

Which issue(s) this PR fixes:

Fixes #2208

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

new: configure syscall buffer dimension from Falco

[Andreagit97]

@incertum @leogr @FedeDP @jasondellaluce

[FedeDP]

Left a comment; otherwise this LGTM!

[leogr]

This looks great.

I've just left some suggestions (nitpicking 😸)

[FedeDP]

/approve

[poiana]

LGTM label has been added.

Git tree hash: 5c95ce7172deeca86625ee937bbb3f6d92d7354a

[Andreagit97]

Rebased on actual master just to have this fix #2215
I've also fixed the case in which we are not able to get the page system size in the last commit (fix(syscall_buffer): set dimension if page size not available)

[jasondellaluce]

/milestone 0.33.0

[leogr]

😍

[poiana]

LGTM label has been added.

Git tree hash: 450a6f8a38ed518bcd8fc9921aa2ee755470b0e0

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Andreagit97, FedeDP, leogr

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