linux-kernel - Re: [PATCH v6 1/3] memory: implement memory_block_advise/probe_max

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Message-ID: <6733c86390c40_10bc62945f@dwillia2-xfh.jf.intel.com.notmuch>
Date: Tue, 12 Nov 2024 13:28:03 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Gregory Price <gourry@...rry.net>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<linux-mm@...ck.org>
CC: <linux-cxl@...r.kernel.org>, <kernel-team@...a.com>,
	<Jonathan.Cameron@...wei.com>, <dan.j.williams@...el.com>,
	<rrichter@....com>, <Terry.Bowman@....com>, <dave.jiang@...el.com>,
	<ira.weiny@...el.com>, <alison.schofield@...el.com>, <gourry@...rry.net>,
	<dave.hansen@...ux.intel.com>, <luto@...nel.org>, <peterz@...radead.org>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
	<rafael@...nel.org>, <lenb@...nel.org>, <david@...hat.com>,
	<osalvador@...e.de>, <gregkh@...uxfoundation.org>,
	<akpm@...ux-foundation.org>, <rppt@...nel.org>
Subject: Re: [PATCH v6 1/3] memory: implement
 memory_block_advise/probe_max_size

Gregory Price wrote:
> Hotplug memory sources may have opinions on what the memblock size
> should be - usually for alignment purposes.  For example, CXL memory
> extents can be 256MB with a matching alignment. If this size/alignment
> is smaller than the block size, it can result in stranded capacity.
> 
> Implement memory_block_advise_max_size for use prior to allocator init,
> for software to advise the system on the max block size.
> 
> Implement memory_block_probe_max_size for use by arch init code to
> calculate the best block size. Use of advice is architecture defined.
> 
> The probe value can never change after first probe. Calls to advise
> after probe will return -EBUSY to aid debugging.
> 
> On systems without hotplug, always return -ENODEV and 0 respectively.

Should the advice just succeed when the result does not matter?

Otherwise, it depends on the caller to not care based on config.

I do not feel that strongly about it, so either way:

Acked-by: Dan Williams <dan.j.williams@...el.com>