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Message-ID: <20250311134126.xfjdq6sq7jtcotck@master>
Date: Tue, 11 Mar 2025 13:41:26 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Wei Yang <richard.weiyang@...il.com>, 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>,
Peter Zijlstra <peterz@...radead.org>,
Pratyush Yadav <ptyadav@...zon.de>,
Rob Herring <robh+dt@...nel.org>, Rob Herring <robh@...nel.org>,
Saravana Kannan <saravanak@...gle.com>,
Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Tom Lendacky <thomas.lendacky@....com>,
Usama Arif <usama.arif@...edance.com>,
Will Deacon <will@...nel.org>, devicetree@...r.kernel.org,
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
On Tue, Mar 11, 2025 at 07:27:23AM +0200, Mike Rapoport wrote:
>Hi Wei,
>
>On Mon, Mar 10, 2025 at 09:51:24AM +0000, Wei Yang wrote:
>> 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.
>
>Wouldn't it be better to check for a change in reserved.max in
>memmap_init_reserved_pages()?
>
Sounds better.
Previously I thought we need to hide detail from user, but actually it is
already in memblock.c :-)
If you agree, I would like to prepare a fix.
>> --
>> Wei Yang
>> Help you, Help me
>
>--
>Sincerely yours,
>Mike.
--
Wei Yang
Help you, Help me
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