On Wed, Mar 29, 2023 at 10:55:37AM -0500, Justin Forbes wrote: > On Sat, Mar 25, 2023 at 1:09 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote: > > > > From: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx> > > > > It is not a good idea to change fundamental parameters of core memory > > management. Having predefined ranges suggests that the values within > > those ranges are sensible, but one has to *really* understand > > implications of changing MAX_ORDER before actually amending it and > > ranges don't help here. > > > > Drop ranges in definition of ARCH_FORCE_MAX_ORDER and make its prompt > > visible only if EXPERT=y > > I do not like suddenly hiding this behind EXPERT for a couple of > reasons. Most importantly, it will silently change the config for > users building with an old kernel config. If a user has for instance > "13" set and building with 4K pages, as is the current configuration > for Fedora and RHEL aarch64 builds, an oldconfig build will now set it > to 10 with no indication that it is doing so. And while I think that > 10 is a fine default for many aarch64 users, there are valid reasons > for choosing other values. Putting this behind expert makes it much > less obvious that this is an option. That's the idea of EXPERT, no? This option was intended to allow allocation of huge pages for architectures that had PMD_ORDER > MAX_ORDER and not to allow user to select size of maximal physically contiguous allocation. Changes to MAX_ORDER fundamentally change the behaviour of core mm and unless users *really* know what they are doing there is no reason to choose non-default values so hiding this option behind EXPERT seems totally appropriate to me. > Justin > > > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> > > Signed-off-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > > --- > > arch/arm64/Kconfig | 4 +--- > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index e60baf7859d1..7324032af859 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -1487,11 +1487,9 @@ config XEN > > # 16K | 27 | 14 | 13 | 11 | > > # 64K | 29 | 16 | 13 | 13 | > > config ARCH_FORCE_MAX_ORDER > > - int "Maximum zone order" if ARM64_4K_PAGES || ARM64_16K_PAGES > > + int "Maximum zone order" if EXPERT && (ARM64_4K_PAGES || ARM64_16K_PAGES) > > default "13" if ARM64_64K_PAGES > > - range 11 13 if ARM64_16K_PAGES > > default "11" if ARM64_16K_PAGES > > - range 10 15 if ARM64_4K_PAGES > > default "10" > > help > > The kernel memory allocator divides physically contiguous memory > > -- > > 2.35.1 > > > > -- Sincerely yours, Mike.
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