linux-kernel - Re: [PATCH v8 0/3] memory,x86,acpi: hotplug memory alignment advisement

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Message-ID: <67ec421a15fe8_288d294c9@dwillia2-xfh.jf.intel.com.notmuch>
Date: Tue, 1 Apr 2025 12:44:26 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Oscar Salvador <osalvador@...e.de>, Gregory Price <gourry@...rry.net>
CC: <linux-mm@...ck.org>, <linux-acpi@...r.kernel.org>,
	<kernel-team@...a.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<dave.hansen@...ux.intel.com>, <luto@...nel.org>, <peterz@...radead.org>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
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	<gregkh@...uxfoundation.org>, <akpm@...ux-foundation.org>,
	<dan.j.williams@...el.com>, <Jonathan.Cameron@...wei.com>,
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	<bfaccini@...dia.com>, <haibo1.xu@...el.com>, <dave.jiang@...el.com>, "Ira
 Weiny" <ira.weiny@...el.com>, Fan Ni <fan.ni@...sung.com>
Subject: Re: [PATCH v8 0/3] memory,x86,acpi: hotplug memory alignment
 advisement

Oscar Salvador wrote:
> On Mon, Jan 27, 2025 at 10:34:02AM -0500, Gregory Price wrote:
> > v8: nits and tag pickups
> > 
> > When physical address regions are not aligned to memory block size,
> > the misaligned portion is lost (stranded capacity).
> > 
> > Block size (min/max/selected) is architecture defined. Most architectures
> > tend to use the minimum block size or some simplistic heurist. On x86,
> > memory block size increases up to 2GB, and is otherwise fitted to the
> > alignment of non-hotplug (i.e. not special purpose memory).
> 
> I wonder if something like this could help us in improving the
> ridiculous situation of having 16MB memory-block size on powerpc.

It's only ridiculous due to what it does to /sys/.../memory,
right?

If you permit me a bit of hand-waving, it would be lovely to deprecate
/sys/.../memory in favor of a new (fd based?) ABI for memory-hotplug
policy management and have something like a fuse "compatfs" mounted at
/sys/.../memory/ for maintaining legacy compatibility for userspace that
still depends on twiddling with individual blocks in sysfs.