linux-kernel - Re: [PATCH v1 1/3] mm: pass meminit_context to __free_pages

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Date: Mon, 10 Jun 2024 10:38:05 +0200
From: David Hildenbrand <david@...hat.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-hyperv@...r.kernel.org, virtualization@...ts.linux.dev,
 xen-devel@...ts.xenproject.org, kasan-dev@...glegroups.com,
 Andrew Morton <akpm@...ux-foundation.org>, Mike Rapoport <rppt@...nel.org>,
 "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>, "Michael S. Tsirkin" <mst@...hat.com>,
 Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Juergen Gross <jgross@...e.com>, Stefano Stabellini
 <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>,
 Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v1 1/3] mm: pass meminit_context to __free_pages_core()

On 10.06.24 06:03, Oscar Salvador wrote:
> On Fri, Jun 07, 2024 at 11:09:36AM +0200, David Hildenbrand wrote:
>> In preparation for further changes, let's teach __free_pages_core()
>> about the differences of memory hotplug handling.
>>
>> Move the memory hotplug specific handling from generic_online_page() to
>> __free_pages_core(), use adjust_managed_page_count() on the memory
>> hotplug path, and spell out why memory freed via memblock
>> cannot currently use adjust_managed_page_count().
>>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
> 
> All looks good but I am puzzled with something.
> 
>> +	} else {
>> +		/* memblock adjusts totalram_pages() ahead of time. */
>> +		atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
>> +	}
> 
> You say that memblock adjusts totalram_pages ahead of time, and I guess
> you mean in memblock_free_all()

And memblock_free_late(), which uses atomic_long_inc().

> 
>   pages = free_low_memory_core_early()
>   totalram_pages_add(pages);
> 
> but that is not ahead, it looks like it is upading __after__ sending
> them to buddy?

Right (it's suboptimal, but not really problematic so far. Hopefully Wei 
can clean it up and move it in here as well)

For the time being

"/* memblock adjusts totalram_pages() manually. */"

?

Thanks!

-- 
Cheers,

David / dhildenb