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Patch series "mm/damon: replace most damon_callback usages in sysfs with new core functions". DAMON provides damon_callback API that notifies monitoring events and allows safe access to damon_ctx internal data. The usage is simple. Users register and deregister callback functions for different monitoring events in damon_ctx. Then the DAMON worker thread (kdamond) of the damon_ctx calls back the registered functions on the events. It is designed in such simple way because it was sufficient for usages of DAMON at the early days. We also wanted to make it flexible so that API user code can implement any required additional features on top of damon_callback on their demands. As expected, more sophisticated usages have invented. Online updates of DAMON parameters and DAMOS auto-tuning inputs, and online retrieval of DAMOS statistics and tried regions information are such usages. Because damon_callback doesn't provide any explicit synchronization mechanism, the user ABIs for exposing such functionalities are implemented in asynchronous ways (DAMON_RECLAIM and DAMON_LRU_SORT}), or synchronous ways (DAMON_SYSFS) with additional synchronization mechanisms that built inside the ABI implementation, on top of damon_callback. So damon_callback is working as expected. However, the additional mechanisms built inside ABI on top of damon_callback is becoming somewhat too big and not easy to maintain. The additional mechanisms can be smaller and easier to maintain when implemented inside the core logic layer. Introduce two new DAMON core API, namely 'damon_call()' and 'damos_walk()'. The two functions support synchronous access to - damon_ctx internal data including DAMON parameters and monitoring results, and - DAMOS-specific data such as regions that each DAMOS action is applied, respectively. And replace most of damon_callback usages in DAMON sysfs interface with the new core API functions. damon_callback usage for online DAMON parameters tuning is not replaced in this series, since it has specific callback timing assumptions that require more works. Patch sequence ============== First two patches are fixups for simplifying the following changes. Those remove a unnecessary condition check and a synchronization, respectively. Third patch implements one of the new DAMON core APIs, namely damon_call(). Three patches replacing damon_callback usages in DAMON sysfs interface using damon_call() follow. Then, seventh and eighth patches introduces the other new DAMON API, damos_walk(), and document it on the design doc. Ninth patch replaces two damon_callback usages in DAMON sysfs interface using damos_walk(). The tenth patch finally cleans up code that no more being used. This patch (of 10): damon_sysfs_schemes_clear_regions() skips removing the scheme tried region directories only if the matching scheme is still ongoing. It is unnecessary check, since what users want is just removing the entire region directories. Remove the unnecessary check. Link: https://lkml.kernel.org/r/20250103174400.54890-1-sj@kernel.org Link: https://lkml.kernel.org/r/20250103174400.54890-2-sj@kernel.org Signed-off-by: SeongJae Park <sj@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.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 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.