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

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Message-ID: <20250310095124.pa7dwgqhxglqrfes@master>
Date: Mon, 10 Mar 2025 09:51:24 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: Mike Rapoport <rppt@...nel.org>, 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>,
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	"H. Peter Anvin" <hpa@...or.com>,
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	Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
	Steven Rostedt <rostedt@...dmis.org>,
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	linux-doc@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH v4 02/14] memblock: add MEMBLOCK_RSRV_KERN flag

On Sun, Feb 23, 2025 at 12:22:29AM +0000, Wei Yang wrote:
>On Wed, Feb 19, 2025 at 09:24:31AM +0200, Mike Rapoport wrote:
>>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().
>> 
>
>I took another look into this commit. There maybe a very corner case in which
>will leave a reserved region with no nid set.
>
>memmap_init_reserved_pages()
>    for_each_mem_region() {
>        ...
>	memblock_set_node(start, end, &memblock.reserved, nid);
>    }
>
>We leverage the iteration here to set nid to all regions in memblock.reserved.
>But memblock_set_node() may call memblock_double_array() to expand the array,
>which may get a range before current start. So we would miss to set the
>correct nid to the new reserved region.
>
>I have tried to create a case in memblock test. This would happen when there
>are 126 memblock.reserved regions. And the last region is across the last two
>node.
>
>One way to fix this is compare type->max in memblock_set_node(). Then check
>this return value in memmap_init_reserved_pages(). If we found the size
>changes, repeat the iteration.
>
>But this is a very trivial one, not sure it worth fix.
>

Hi, Mike

I have done a user space test which shows we may have a chance to leave a
region with non-nid set.

Not sure you are ok with my approach of fixing.

-- 
Wei Yang
Help you, Help me