On Tue, Feb 27, 2024 at 10:30:53AM +0100, Vlastimil Babka wrote: > > > On 2/26/24 18:11, Suren Baghdasaryan wrote: > > On Mon, Feb 26, 2024 at 9:07 AM Vlastimil Babka <vbabka@xxxxxxx> wrote: > >> > >> On 2/21/24 20:40, Suren Baghdasaryan wrote: > >>> Introduce helper functions to easily instrument page allocators by > >>> storing a pointer to the allocation tag associated with the code that > >>> allocated the page in a page_ext field. > >>> > >>> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > >>> Co-developed-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> > >>> Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> > >> > >> The static key usage seems fine now. Even if the page_ext overhead is still > >> always paid when compiled in, you mention in the cover letter there's a plan > >> for boot-time toggle later, so > > > > Yes, I already have a simple patch for that to be included in the next > > revision: https://github.com/torvalds/linux/commit/7ca367e80232345f471b77b3ea71cf82faf50954 > > This opt-out logic would require a distro kernel with allocation > profiling compiled-in to ship together with something that modifies > kernel command line to disable it by default, so it's not very > practical. Could the CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT be > turned into having 3 possible choices, where one of them would > initialize mem_profiling_enabled to false? > > Or, taking a step back, is it going to be a common usecase to pay the > memory overhead unconditionally, but only enable the profiling later > during runtime? Also what happens if someone would enable and disable it > multiple times during one boot? Would the statistics get all skewed > because some frees would be not accounted while it's disabled? I already wrote the code for fast lookup from codetag index -> codetag - i.e. pointer compression - so this is all going away shortly. It just won't be in the initial pull request because of other dependencies (it requires my eytzinger code, which I was already lifting from fs/bcachefs/ for 6.9), but it can still probably make 6.9 in a second smaller pull.
