linux-kernel - Re: [PATCH v2 4/8] mm/memory_hotplug: Create memory block devices after arch_add

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Date:   Thu, 9 May 2019 21:50:34 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Wei Yang <richard.weiyang@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, akpm@...ux-foundation.org,
        Dan Williams <dan.j.williams@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "mike.travis@....com" <mike.travis@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Banman <andrew.banman@....com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Qian Cai <cai@....pw>, Arun KS <arunks@...eaurora.org>,
        Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH v2 4/8] mm/memory_hotplug: Create memory block devices
 after arch_add_memory()

On Thu, May 09, 2019 at 04:58:56PM +0200, David Hildenbrand wrote:
>On 09.05.19 16:31, Wei Yang wrote:
>> On Tue, May 07, 2019 at 08:38:00PM +0200, David Hildenbrand wrote:
>>> Only memory to be added to the buddy and to be onlined/offlined by
>>> user space using memory block devices needs (and should have!) memory
>>> block devices.
>>>
>>> Factor out creation of memory block devices Create all devices after
>>> arch_add_memory() succeeded. We can later drop the want_memblock parameter,
>>> because it is now effectively stale.
>>>
>>> Only after memory block devices have been added, memory can be onlined
>>> by user space. This implies, that memory is not visible to user space at
>>> all before arch_add_memory() succeeded.
>>>
>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
>>> Cc: David Hildenbrand <david@...hat.com>
>>> Cc: "mike.travis@....com" <mike.travis@....com>
>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>> Cc: Ingo Molnar <mingo@...nel.org>
>>> Cc: Andrew Banman <andrew.banman@....com>
>>> Cc: Oscar Salvador <osalvador@...e.de>
>>> Cc: Michal Hocko <mhocko@...e.com>
>>> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
>>> Cc: Qian Cai <cai@....pw>
>>> Cc: Wei Yang <richard.weiyang@...il.com>
>>> Cc: Arun KS <arunks@...eaurora.org>
>>> Cc: Mathieu Malaterre <malat@...ian.org>
>>> Signed-off-by: David Hildenbrand <david@...hat.com>
>>> ---
>>> drivers/base/memory.c  | 70 ++++++++++++++++++++++++++----------------
>>> include/linux/memory.h |  2 +-
>>> mm/memory_hotplug.c    | 15 ++++-----
>>> 3 files changed, 53 insertions(+), 34 deletions(-)
>>>
>>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>>> index 6e0cb4fda179..862c202a18ca 100644
>>> --- a/drivers/base/memory.c
>>> +++ b/drivers/base/memory.c
>>> @@ -701,44 +701,62 @@ static int add_memory_block(int base_section_nr)
>>> 	return 0;
>>> }
>>>
>>> +static void unregister_memory(struct memory_block *memory)
>>> +{
>>> +	BUG_ON(memory->dev.bus != &memory_subsys);
>>> +
>>> +	/* drop the ref. we got via find_memory_block() */
>>> +	put_device(&memory->dev);
>>> +	device_unregister(&memory->dev);
>>> +}
>>> +
>>> /*
>>> - * need an interface for the VM to add new memory regions,
>>> - * but without onlining it.
>>> + * Create memory block devices for the given memory area. Start and size
>>> + * have to be aligned to memory block granularity. Memory block devices
>>> + * will be initialized as offline.
>>>  */
>>> -int hotplug_memory_register(int nid, struct mem_section *section)
>>> +int hotplug_memory_register(unsigned long start, unsigned long size)
>> 
>> One trivial suggestion about the function name.
>> 
>> For memory_block device, sometimes we use the full name
>> 
>>     find_memory_block
>>     init_memory_block
>>     add_memory_block
>> 
>> But sometimes we use *nick* name
>> 
>>     hotplug_memory_register
>>     register_memory
>>     unregister_memory
>> 
>> This is a little bit confusion.
>> 
>> Can we use one name convention here?
>
>We can just go for
>
>crate_memory_blocks() and free_memory_blocks(). Or do
>you have better suggestions?

s/crate/create/

Looks good to me.

>
>(I would actually even prefer "memory_block_devices", because memory
>blocks have different meanins)
>

Agree with you, this comes to my mind sometime ago :-)

>> 
>> [...]
>> 
>>> /*
>>> @@ -1106,6 +1100,13 @@ int __ref add_memory_resource(int nid, struct resource *res)
>>> 	if (ret < 0)
>>> 		goto error;
>>>
>>> +	/* create memory block devices after memory was added */
>>> +	ret = hotplug_memory_register(start, size);
>>> +	if (ret) {
>>> +		arch_remove_memory(nid, start, size, NULL);
>> 
>> Functionally, it works I think.
>> 
>> But arch_remove_memory() would remove pages from zone. At this point, we just
>> allocate section/mmap for pages, the zones are empty and pages are not
>> connected to zone.
>> 
>> Function  zone = page_zone(page); always gets zone #0, since pages->flags is 0
>> at  this point. This is not exact.
>> 
>> Would we add some comment to mention this? Or we need to clean up
>> arch_remove_memory() to take out __remove_zone()?
>
>That is precisely what is on my list next (see cover letter).This is
>already broken when memory that was never onlined is removed again.
>So I am planning to fix that independently.
>

Sounds great :-)

Hope you would cc me in the following series.

>
>-- 
>
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me