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From: Pavel Tatashin <pasha.tatashin@gmail.com>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	linux-mm@kvack.org, akpm@linux-foundation.org
Cc: pavel.tatashin@microsoft.com, mhocko@suse.com,
	dave.jiang@intel.com, linux-kernel@vger.kernel.org,
	willy@infradead.org, davem@davemloft.net,
	yi.z.zhang@linux.intel.com, khalid.aziz@oracle.com,
	rppt@linux.vnet.ibm.com, vbabka@suse.cz,
	sparclinux@vger.kernel.org, dan.j.williams@intel.com,
	ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net,
	mingo@kernel.org, kirill.shutemov@linux.intel.com
Subject: Re: [mm PATCH v3 2/6] mm: Drop meminit_pfn_in_nid as it is redundant
Date: Tue, 16 Oct 2018 17:06:48 -0400	[thread overview]
Message-ID: <06e4428b-860e-1e66-defd-77666fcfa0c5@gmail.com> (raw)
In-Reply-To: <e4f806d4-2527-07c2-56bc-9c41789d669c@linux.intel.com>



On 10/16/18 4:49 PM, Alexander Duyck wrote:
> On 10/16/2018 1:33 PM, Pavel Tatashin wrote:
>>
>>
>> On 10/15/18 4:27 PM, Alexander Duyck wrote:
>>> As best as I can tell the meminit_pfn_in_nid call is completely
>>> redundant.
>>> The deferred memory initialization is already making use of
>>> for_each_free_mem_range which in turn will call into __next_mem_range
>>> which
>>> will only return a memory range if it matches the node ID provided
>>> assuming
>>> it is not NUMA_NO_NODE.
>>>
>>> I am operating on the assumption that there are no zones or pgdata_t
>>> structures that have a NUMA node of NUMA_NO_NODE associated with
>>> them. If
>>> that is the case then __next_mem_range will never return a memory range
>>> that doesn't match the zone's node ID and as such the check is
>>> redundant.
>>>
>>> So one piece I would like to verfy on this is if this works for ia64.
>>> Technically it was using a different approach to get the node ID, but it
>>> seems to have the node ID also encoded into the memblock. So I am
>>> assuming this is okay, but would like to get confirmation on that.
>>>
>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>>
>> If I am not mistaken, this code is for systems with memory interleaving.
>> Quick looks shows that x86, powerpc, s390, and sparc have it set.
>>
>> I am not sure about other arches, but at least on SPARC, there are some
>> processors with memory interleaving feature:
>>
>> http://www.fujitsu.com/global/products/computing/servers/unix/sparc-enterprise/technology/performance/memory.html
>>
>>
>> Pavel
> 
> I get what it is for. However as best I can tell the check is actually
> redundant. In the case of the deferred page initialization we are
> already pulling the memory regions via "for_each_free_mem_range". That
> function is already passed a NUMA node ID. Because of that we are
> already checking the memory range to determine if it is in the node or
> not. As such it doesn't really make sense to go through for each PFN and
> then go back to the memory range and see if the node matches or not.
> 

Agree, it looks redundant, nice clean-up, I like it.

Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>

Thank you,
Pavel


> You can take a look at __next_mem_range which is called by
> for_each_free_mem_range and passed &memblock.memory and
> &memblock.reserved to avoid:
> https://elixir.bootlin.com/linux/latest/source/mm/memblock.c#L899
> 
> Then you can work your way through:
> meminit_pfn_in_nid(pfn, node, state)
>  __early_pfn_to_nid(pfn, state)
>   memblock_search_pfn_nid(pfn, &start_pfn, &end_pfn)
>    memblock_search(&memblock.memory, pfn)
> 
> From what I can tell the deferred init is going back through the
> memblock.memory list we pulled this range from and just validating it
> against itself. This makes sense for the standard init as that is just
> going from start_pfn->end_pfn, but for the deferred init we are pulling
> the memory ranges ahead of time so we shouldn't need to re-validate the
> memory that is contained within that range.

  reply	other threads:[~2018-10-16 21:06 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-15 20:26 [mm PATCH v3 0/6] Deferred page init improvements Alexander Duyck
2018-10-15 20:26 ` [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures Alexander Duyck
2018-10-16 19:01   ` Pavel Tatashin
2018-10-17  7:30     ` Mike Rapoport
2018-10-17 14:52       ` Alexander Duyck
2018-10-17  8:47   ` Michal Hocko
2018-10-17 15:07     ` Alexander Duyck
2018-10-17 15:12       ` Pavel Tatashin
2018-10-17 15:40         ` David Laight
2018-10-17 16:31           ` Alexander Duyck
2018-10-17 17:08             ` Pavel Tatashin
2018-10-17 16:34       ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 2/6] mm: Drop meminit_pfn_in_nid as it is redundant Alexander Duyck
2018-10-16 20:33   ` Pavel Tatashin
2018-10-16 20:49     ` Alexander Duyck
2018-10-16 21:06       ` Pavel Tatashin [this message]
2018-10-17  9:04   ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 3/6] mm: Use memblock/zone specific iterator for handling deferred page init Alexander Duyck
2018-10-17  9:11   ` Michal Hocko
2018-10-17 15:17     ` Alexander Duyck
2018-10-17 16:42   ` Mike Rapoport
2018-10-15 20:27 ` [mm PATCH v3 4/6] mm: Move hot-plug specific memory init into separate functions and optimize Alexander Duyck
2018-10-17  9:18   ` Michal Hocko
2018-10-17 15:26     ` Alexander Duyck
2018-10-24 12:36       ` Michal Hocko
2018-10-24 15:08         ` Alexander Duyck
2018-10-24 15:27           ` Michal Hocko
2018-10-24 17:35             ` Alexander Duyck
2018-10-25 12:41               ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 5/6] mm: Use common iterator for deferred_init_pages and deferred_free_pages Alexander Duyck
2018-10-15 20:27 ` [mm PATCH v3 6/6] mm: Add reserved flag setting to set_page_links Alexander Duyck

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