linux-kernel - Re: [PATCH v4 02/14] memblock: add MEMBLOCK_RSRV

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Message-ID: <Z7WHL_Xqgoln9oLg@kernel.org>
Date: Wed, 19 Feb 2025 09:24:31 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Wei Yang <richard.weiyang@...il.com>
Cc: linux-kernel@...r.kernel.org, Alexander Graf <graf@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Anthony Yznaga <anthony.yznaga@...cle.com>,
	Arnd Bergmann <arnd@...db.de>, Ashish Kalra <ashish.kalra@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Borislav Petkov <bp@...en8.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Eric Biederman <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...hat.com>, James Gowans <jgowans@...zon.com>,
	Jonathan Corbet <corbet@....net>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	"H. Peter Anvin" <hpa@...or.com>,
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	kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH v4 02/14] memblock: add MEMBLOCK_RSRV_KERN flag

Hi,

On Tue, Feb 18, 2025 at 03:50:04PM +0000, Wei Yang wrote:
> On Thu, Feb 06, 2025 at 03:27:42PM +0200, Mike Rapoport wrote:
> >From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> >
> >to denote areas that were reserved for kernel use either directly with
> >memblock_reserve_kern() or via memblock allocations.
> >
> >Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> >---
> > include/linux/memblock.h | 16 +++++++++++++++-
> > mm/memblock.c            | 32 ++++++++++++++++++++++++--------
> > 2 files changed, 39 insertions(+), 9 deletions(-)
> >
> >diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> >index e79eb6ac516f..65e274550f5d 100644
> >--- a/include/linux/memblock.h
> >+++ b/include/linux/memblock.h
> >@@ -50,6 +50,7 @@ enum memblock_flags {
> > 	MEMBLOCK_NOMAP		= 0x4,	/* don't add to kernel direct mapping */
> > 	MEMBLOCK_DRIVER_MANAGED = 0x8,	/* always detected via a driver */
> > 	MEMBLOCK_RSRV_NOINIT	= 0x10,	/* don't initialize struct pages */
> >+	MEMBLOCK_RSRV_KERN	= 0x20,	/* memory reserved for kernel use */
> 
> Above memblock_flags, there are comments on explaining those flags.
> 
> Seems we miss it for MEMBLOCK_RSRV_KERN.

Right, thanks!
 
> > 
> > #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
> >@@ -1459,14 +1460,14 @@ phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
> > again:
> > 	found = memblock_find_in_range_node(size, align, start, end, nid,
> > 					    flags);
> >-	if (found && !memblock_reserve(found, size))
> >+	if (found && !__memblock_reserve(found, size, nid, MEMBLOCK_RSRV_KERN))
> 
> Maybe we could use memblock_reserve_kern() directly. If my understanding is
> correct, the reserved region's nid is not used.

We use nid of reserved regions in reserve_bootmem_region() (commit
61167ad5fecd ("mm: pass nid to reserve_bootmem_region()")) but KHO needs to
know the distribution of reserved memory among the nodes before
memmap_init_reserved_pages().
 
> BTW, one question here. How we handle concurrent memblock allocation? If two
> threads find the same available range and do the reservation, it seems to be a
> problem to me. Or I missed something?

memblock allocations end before smp_init(), there is no possible concurrency.
 
> -- 
> Wei Yang
> Help you, Help me

-- 
Sincerely yours,
Mike.