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[91.12.98.49]) by smtp.gmail.com with ESMTPSA id j21sm93193eja.109.2020.08.21.14.33.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Aug 2020 14:33:58 -0700 (PDT) From: David Hildenbrand Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v4 00/23] device-dax: Support sub-dividing soft-reserved ranges Date: Fri, 21 Aug 2020 23:33:57 +0200 Message-Id: <646DDE9B-90C2-493A-958C-90EFA1CCA475@redhat.com> References: Cc: David Hildenbrand , Andrew Morton , Ira Weiny , Ard Biesheuvel , Mike Rapoport , Borislav Petkov , Vishal Verma , David Airlie , Will Deacon , Catalin Marinas , Ard Biesheuvel , Joao Martins , Tom Lendacky , Dave Jiang , "Rafael J. Wysocki" , Jonathan Cameron , Wei Yang , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Greg Kroah-Hartman , Pavel Tatashin , Peter Zijlstra , Ben Skeggs , Benjamin Herrenschmidt , Jason Gunthorpe , Jia He , Ingo Molnar , Dave Hansen , Paul Mackerras , Brice Goglin , Jeff Moyer , Michael Ellerman , "Rafael J. Wysocki" , Daniel Vetter , Andy Lutomirski , "Rafael J. Wysocki" , Linux MM , linux-nvdimm , Linux Kernel Mailing List , Linux ACPI , Maling list - DRI developers In-Reply-To: To: Dan Williams X-Mailer: iPhone Mail (17G68) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0.502 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: EDEA61004BE43 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > Am 21.08.2020 um 23:17 schrieb Dan Williams : >=20 > =EF=BB=BFOn Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand wrote: >>=20 >>> On 21.08.20 20:27, Dan Williams wrote: >>> On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand wr= ote: >>>>=20 >>>>>>=20 >>>>>> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is = not >>>>>> automatically used in the buddy during boot, but remains untouched >>>>>> (similar to pmem). But as it involves ACPI as well, it could also be >>>>>> used on arm64 (-e820), correct? >>>>>=20 >>>>> Correct, arm64 also gets the EFI support for enumerating memory this >>>>> way. However, I would clarify that whether soft-reserved is given to >>>>> the buddy allocator by default or not is the kernel's policy choice, >>>>> "buddy-by-default" is ok and is what will happen anyways with older >>>>> kernels on platforms that enumerate a memory range this way. >>>>=20 >>>> Is "soft-reserved" then the right terminology for that? It sounds very >>>> x86-64/e820 specific. Maybe a compressed for of "performance >>>> differentiated memory" might be a better fit to expose to user space, = no? >>>=20 >>> No. The EFI "Specific Purpose" bit is an attribute independent of >>> e820, it's x86-Linux that entangles those together. There is no >>> requirement for platform firmware to use that designation even for >>> drastic performance differentiation between ranges, and conversely >>> there is no requirement that memory *with* that designation has any >>> performance difference compared to the default memory pool. So it >>> really is a reservation policy about a memory range to keep out of the >>> buddy allocator by default. >>=20 >> Okay, still "soft-reserved" is x86-64 specific, no? >=20 > There's nothing preventing other EFI archs, or a similar designation > in another firmware spec, picking up this policy. >=20 >> (AFAIK, >> "soft-reserved" will be visible in /proc/iomem, or am I confusing >> stuff?) >=20 > No, you're correct. >=20 >> IOW, it "performance differentiated" is not universally >> applicable, maybe "specific purpose memory" is ? >=20 > Those bikeshed colors don't seem an improvement to me. >=20 > "Soft-reserved" actually tells you something about the kernel policy > for the memory. The criticism of "specific purpose" that led to > calling it "soft-reserved" in Linux is the fact that "specific" is > undefined as far as the firmware knows, and "specific" may have > different applications based on the platform user. "Soft-reserved" > like "Reserved" tells you that a driver policy might be in play for > that memory. >=20 > Also note that the current color of the bikeshed has already shipped sinc= e v5.5: >=20 > 262b45ae3ab4 x86/efi: EFI soft reservation to E820 enumeration >=20 I was asking because I was struggling to even understand what =E2=80=9Esoft= -reserved=E2=80=9C is and I could bet most people have no clue what that is= supposed to be. In contrast =E2=80=9Epersistent memory=E2=80=9C or =E2=80=9Especial purpose= memory=E2=80=9C in /proc/iomem is something normal (Linux using) human bei= ngs can understand. But anyhow, just details, and you=E2=80=98re telling me that that ship alre= ady sailed. So no further comments from my side. Thanks for all the info!