linux-kernel - Re: [PATCH v2 1/3] mm/memblock: implement memblock_advise_size

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Message-ID: <ZxZntygJWqxq0zGt@PC2K9PVX.TheFacebook.com>
Date: Mon, 21 Oct 2024 10:39:51 -0400
From: Gregory Price <gourry@...rry.net>
To: Mike Rapoport <rppt@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-mm@...ck.org,
	dan.j.williams@...el.com, ira.weiny@...el.com, david@...hat.com,
	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, akpm@...ux-foundation.org,
	alison.schofield@...el.com, Jonathan.Cameron@...wei.com,
	rrichter@....com, ytcoode@...il.com, haibo1.xu@...el.com,
	dave.jiang@...el.com
Subject: Re: [PATCH v2 1/3] mm/memblock: implement memblock_advise_size_order
 and probe functions

On Sun, Oct 20, 2024 at 11:57:27AM +0300, Mike Rapoport wrote:
> On Wed, Oct 16, 2024 at 03:24:43PM -0400, 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 as small as 256MB with a matching physical alignment.
> > 
> > Implement memblock_advise_size_order for use during early init, prior
> > to allocator and smp init, for software to advise the system as to what
> > the preferred block size should be.
> > 
> > The probe function is meant for arch_init code to fetch this value
> > once during memblock size calculation. Use of the advisement value
> > is arch-specific, and no guarantee is made that it will be used.
> 
> I'm confused.
>  
> Aren't we talking about memory blocks for hotplugable memory here?
> This functionality rather belongs to drivers/base/memory.c, doesn't it?
>

You're right, I should have put it there - i got distracted by the ifdef
mess around get_block_size_bytes/set...order and just tossed it into memblock
to avoid it.  I should be able to ifdef the definition in the header and move
it into memory.c
 
> > Calls to either function after probe results in -EBUSY to signal that
> > advisement is ignored or that memblock_get_size_bytes should be used.
> > 
> > Suggested-by: Ira Weiny <ira.weiny@...el.com>
> > Signed-off-by: Gregory Price <gourry@...rry.net>
> > ---
> >  include/linux/memblock.h |  2 ++
> >  mm/memblock.c            | 49 ++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 51 insertions(+)
> >