From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Rapoport Date: Tue, 04 Apr 2023 07:22:00 +0000 Subject: Re: [PATCH v3 02/14] arm64: drop ranges in definition of ARCH_FORCE_MAX_ORDER Message-Id: List-Id: References: <20230325060828.2662773-1-rppt@kernel.org> <20230325060828.2662773-3-rppt@kernel.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable To: Justin Forbes Cc: Andrew Morton , Arnd Bergmann , Catalin Marinas , Christophe Leroy , "David S. Miller" , Dinh Nguyen , Geert Uytterhoeven , Guo Ren , John Paul Adrian Glaubitz , "Kirill A. Shutemov" , Max Filippov , Michael Ellerman , Rich Felker , Russell King , Will Deacon , Yoshinori Sato , Zi Yan , linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mm@kvack.org, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org On Wed, Mar 29, 2023 at 10:55:37AM -0500, Justin Forbes wrote: > On Sat, Mar 25, 2023 at 1:09=E2=80=AFAM Mike Rapoport w= rote: > > > > From: "Mike Rapoport (IBM)" > > > > 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=3Dy >=20 > 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. =20 > Justin >=20 > > Acked-by: Kirill A. Shutemov > > Reviewed-by: Zi Yan > > Signed-off-by: Mike Rapoport (IBM) > > --- > > 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 | 1= 1 | > > # 64K | 29 | 16 | 13 | 1= 3 | > > 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 mem= ory > > -- > > 2.35.1 > > > > --=20 Sincerely yours, Mike.