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Message-ID: <20250226020915.ytxusrrl7rv4g64l@master>
Date: Wed, 26 Feb 2025 02:09:15 +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, Feb 25, 2025 at 09:46:28AM +0200, Mike Rapoport wrote:
>On Mon, Feb 24, 2025 at 01:31:31AM +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().
>> >
>> >> 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.
>> >
>>
>> Thanks, I still have one question here.
>>
>> Below is a simplified call flow.
>>
>> mm_core_init()
>> mem_init()
>> memblock_free_all()
>> free_low_memory_core_early()
>> memmap_init_reserved_pages()
>> memblock_set_node(..., memblock.reserved, ) --- (1)
>> __free_memory_core()
>> kmem_cache_init()
>> slab_state = UP; --- (2)
>>
>> And memblock_allloc_range_nid() is not supposed to be called after
>> slab_is_available(). Even someone do dose it, it will get memory from slab
>> instead of reserve region in memblock.
>>
>> From the above call flow and background, there are three cases when
>> memblock_alloc_range_nid() would be called:
>>
>> * If it is called before (1), memblock.reserved's nid would be adjusted correctly.
>> * If it is called after (2), we don't touch memblock.reserved.
>> * If it happens between (1) and (2), it looks would break the consistency of
>> nid information in memblock.reserved. Because when we use
>> memblock_reserve_kern(), NUMA_NO_NODE would be stored in region.
>>
>> So my question is if the third case happens, would it introduce a bug? If it
>> won't happen, seems we don't need to specify the nid here?
>
>We don't really care about proper assignment of nodes between (1) and (2)
>from one side and the third case does not happen on the other side. Nothing
>should call membloc_alloc() after memblock_free_all().
>
My point is if no one would call memblock_alloc() after memblock_free_all(),
which set nid in memblock.reserved properly, it seems not necessary to do
__memblock_reserve() with exact nid during memblock_alloc()?
As you did __memblock_reserve(found, size, nid, MEMBLOCK_RSRV_KERN) in this
patch.
>But it's easy to make the window between (1) and (2) disappear by replacing
>checks for slab_is_available() in memblock with a variable local to
>memblock.
>
>> --
>> Wei Yang
>> Help you, Help me
>
>--
>Sincerely yours,
>Mike.
--
Wei Yang
Help you, Help me
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