On 17.07.2023 18:03, Alejandro Vallejo wrote: > Currently there's a CONFIG_HAS_PDX Kconfig option, but it's impossible to > disable it because the whole codebase performs unconditional > compression/decompression operations on addresses. This has the > unfortunate side effect that systems without a need for compression still > have to pay the performance impact of juggling bits on every pfn<->pdx > conversion (this requires reading several global variables). This series > attempts to: > > * Leave the state of pdx and pdx compression documented > * Factor out compression so it _can_ be removed through Kconfig > * Make it so compression is disabled on x86 and enabled on both Aarch32 > and Aarch64 by default.
I disagree with this choice of default for x86. To avoid surprising downstreams, this should at best be a two-step process: Keep the default as Y right now, and switch to N a couple of releases later. But that's only the simple / mechanical side. Considering my earlier effort to reduce / remove the involved overhead dynamically at runtime (which you may or may not be aware of; see [2]), I view a compile time choice as less desirable. At the very least I would expect some justification towards this build time choice being acceptable / reasonable despite the earlier effort towards greater flexibility. Only such would be likely to have me merely defer to other x86 maintainers, rather than outright objecting. Jan [2] https://lists.xenproject.org/archives/html/xen-devel/2018-09/msg01616.html
