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In-Reply-To: From: Dan Williams Date: Fri, 14 Feb 2020 15:05:09 -0800 Message-ID: Subject: Re: [PATCH v2 1/4] mm/memremap_pages: Introduce memremap_compat_align() To: Jeff Moyer Message-ID-Hash: IWT7Y3DS2VXXLUSC3COJBV7UPBAGBFFF X-Message-ID-Hash: IWT7Y3DS2VXXLUSC3COJBV7UPBAGBFFF X-MailFrom: dan.j.williams@intel.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; suspicious-header CC: linux-nvdimm , "Aneesh Kumar K.V" , Benjamin Herrenschmidt , Paul Mackerras , Linux Kernel Mailing List , linuxppc-dev X-Mailman-Version: 3.1.1 Precedence: list List-Id: "Linux-nvdimm developer list." Archived-At: List-Archive: List-Help: List-Post: List-Subscribe: List-Unsubscribe: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Feb 14, 2020 at 12:59 PM Jeff Moyer wrote: > > Dan Williams writes: > > > On Thu, Feb 13, 2020 at 8:58 AM Jeff Moyer wrote: > > >> I have just a couple of questions. > >> > >> First, can you please add a comment above the generic implementation of > >> memremap_compat_align describing its purpose, and why a platform might > >> want to override it? > > > > Sure, how about: > > > > /* > > * The memremap() and memremap_pages() interfaces are alternately used > > * to map persistent memory namespaces. These interfaces place different > > * constraints on the alignment and size of the mapping (namespace). > > * memremap() can map individual PAGE_SIZE pages. memremap_pages() can > > * only map subsections (2MB), and at least one architecture (PowerPC) > > * the minimum mapping granularity of memremap_pages() is 16MB. > > * > > * The role of memremap_compat_align() is to communicate the minimum > > * arch supported alignment of a namespace such that it can freely > > * switch modes without violating the arch constraint. Namely, do not > > * allow a namespace to be PAGE_SIZE aligned since that namespace may be > > * reconfigured into a mode that requires SUBSECTION_SIZE alignment. > > */ > > Well, if we modify the x86 variant to be PAGE_SIZE, I think that text > won't work. How about: ...but I'm not looking to change it to PAGE_SIZE, I'm going to fix the alignment check to skip if the namespace has "inner" alignment padding, i.e. "start_pad" and/or "end_trunc" are non-zero. _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org