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The highest memory overhead from memory allocation profiling comes from page_ext objects. This overhead exists even if the feature is disabled but compiled-in. To avoid it, introduce an early boot parameter that prevents page_ext object creation. The new boot parameter is a tri-state with possible values of 0|1|never. When it is set to "never" the memory allocation profiling support is disabled, and overhead is minimized (currently no page_ext objects are allocated, in the future more overhead might be eliminated). As a result we also lose ability to enable memory allocation profiling at runtime (because there is no space to store alloctag references). Runtime sysctrl becomes read-only if the early boot parameter was set to "never". Note that the default value of this boot parameter depends on the CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT configuration. When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n the boot parameter is set to "never", therefore eliminating any overhead. CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y results in boot parameter being set to 1 (enabled). This allows distributions to avoid any overhead by setting CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n config and with no changes to the kernel command line. We reuse sysctl.vm.mem_profiling boot parameter name in order to avoid introducing yet another control. This change turns it into a tri-state early boot parameter. Link: https://lkml.kernel.org/r/20240321163705.3067592-16-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Tested-by: Kees Cook <keescook@chromium.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Alex Gaynor <alex.gaynor@gmail.com> Cc: Alice Ryhl <aliceryhl@google.com> Cc: Andreas Hindborg <a.hindborg@samsung.com> Cc: Benno Lossin <benno.lossin@proton.me> Cc: "Björn Roy Baron" <bjorn3_gh@protonmail.com> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Christoph Lameter <cl@linux.com> Cc: Dennis Zhou <dennis@kernel.org> Cc: Gary Guo <gary@garyguo.net> Cc: Kent Overstreet <kent.overstreet@linux.dev> Cc: Miguel Ojeda <ojeda@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Cc: Wedson Almeida Filho <wedsonaf@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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 reStructuredText 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.