On Tue, Oct 15, 2024 at 12:32 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 15.10.24 01:53, John Hubbard wrote: > > On 10/14/24 4:48 PM, Yosry Ahmed wrote: > >> On Mon, Oct 14, 2024 at 1:37 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > >>> > >>> Add CONFIG_PGALLOC_TAG_USE_PAGEFLAGS to store allocation tag > >>> references directly in the page flags. This eliminates memory > >>> overhead caused by page_ext and results in better performance > >>> for page allocations. > >>> If the number of available page flag bits is insufficient to > >>> address all kernel allocations, profiling falls back to using > >>> page extensions with an appropriate warning to disable this > >>> config. > >>> If dynamically loaded modules add enough tags that they can't > >>> be addressed anymore with available page flag bits, memory > >>> profiling gets disabled and a warning is issued. > >> > >> Just curious, why do we need a config option? If there are enough bits > >> in page flags, why not use them automatically or fallback to page_ext > >> otherwise? > > > > Or better yet, *always* fall back to page_ext, thus leaving the > > scarce and valuable page flags available for other features? > > > > Sorry Suren, to keep coming back to this suggestion, I know > > I'm driving you crazy here! But I just keep thinking it through > > and failing to see why this feature deserves to consume so > > many page flags. > > My 2 cents: there is nothing wrong about consuming unused page flags in > a configuration. No need to let them stay unused in a configuration :) > > The real issue starts once another feature wants to make use of some of > them ... in such configuration there would be less available for > allocation tags and the performance of allocations tags might > consequently get worse again. Thanks for the input and indeed this is the case. If this happens, we will get a warning telling us that page flags could not be used and page_ext will be used instead. I think that's the best I can do given that page flag bits is a limited resource. > > -- > Cheers, > > David / dhildenb >
