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From: David Hildenbrand <david@redhat.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Oscar Salvador <osalvador@suse.de>,
	linux-s390@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
	linux-ia64@vger.kernel.org,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	linux-sh@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Wei Yang <richardw.yang@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org,
	Dan Williams <dan.j.williams@intel.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()
Date: Wed, 5 Feb 2020 14:17:47 +0100
Message-ID: <32e06c13-222c-4486-3914-df2807cf2a2b@redhat.com> (raw)
In-Reply-To: <20200205125149.GS22482@gate.crashing.org>

On 05.02.20 13:51, Segher Boessenkool wrote:
> On Tue, Feb 04, 2020 at 02:38:51PM +0100, David Hildenbrand wrote:
>> On 04.02.20 14:13, Segher Boessenkool wrote:
>>> On Tue, Feb 04, 2020 at 01:41:06PM +0100, David Hildenbrand wrote:
>>>> It's a pattern commonly used in compilers and emulators to calculate the
>>>> number of bytes to the next block/alignment. (we're missing a macro
>>>> (like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up
>>>> with a good name (e.g., SIZE_TO_NEXT_ALIGN) .
> 
>>> You can just write the easy to understand
>>>
>>>   ...  ALIGN_UP(x) - x  ...
>>
>> you mean
>>
>> ALIGN_UP(x, PAGES_PER_SECTION) - x
>>
>> but ...
>>
>>> which is better *without* having a separate name.  Does that not
>>> generate good machine code for you?
>>
>> 1. There is no ALIGN_UP. "SECTION_ALIGN_UP(x) - x" would be possible
> 
> Erm, you started it ;-)

Yeah, I was thinking in the wrong code base :)

> 
>> 2. It would be wrong if x is already aligned.
>>
>> e.g., let's use 4096 for simplicity as we all know that value by heart
>> (for both x and the block size).
>>
>> a) -(4096 | -4096) -> 4096
>>
>> b) #define ALIGN_UP(x, a) ((x + a - 1) & -(a))
>>
>> ALIGN_UP(4096, 4096) - 4096 -> 0
>>
>> Not as easy as it seems ...
> 
> If you always want to return a number >= 1, it it simply
>   ALIGN_UP(x + 1) - x


I'm sorry to have to correct you again for some corner cases:

ALIGN_UP(1, 4096) - 4096 = 0

Again, not as easy as it seems ...

-- 
Thanks,

David / dhildenb



  reply index

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-06  8:56 [PATCH v6 00/10] mm/memory_hotplug: Shrink zones before removing memory David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages() David Hildenbrand
2019-10-06 19:58   ` Damian Tometzki
2019-10-06 20:13     ` David Hildenbrand
2019-10-14  9:05   ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 02/10] mm/memmap_init: Update variable name in memmap_init_zone David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 03/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_pgdat_span() David Hildenbrand
2019-10-14  9:31   ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span() David Hildenbrand
2019-10-14  9:32   ` David Hildenbrand
2019-10-14 19:17     ` Andrew Morton
2019-11-19 14:16       ` David Hildenbrand
2019-11-19 20:44         ` Andrew Morton
2019-10-06  8:56 ` [PATCH v6 05/10] mm/memory_hotplug: Shrink zones when offlining memory David Hildenbrand
2019-10-14  9:39   ` David Hildenbrand
2019-10-14 19:16     ` Andrew Morton
2019-10-27 22:45   ` David Hildenbrand
2019-11-30 23:21     ` Andrew Morton
2019-11-30 23:43       ` David Hildenbrand
2019-12-18 17:08       ` David Hildenbrand
2019-12-18 20:16         ` Andrew Morton
2019-12-03 15:10   ` Oscar Salvador
2019-12-03 15:27     ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 06/10] mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone() David Hildenbrand
2019-10-16 14:01   ` David Hildenbrand
2020-02-04  8:59   ` Oscar Salvador
2019-10-06  8:56 ` [PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn David Hildenbrand
2020-02-04  9:06   ` Oscar Salvador
2020-02-05  8:57   ` Wei Yang
2020-02-05  8:59     ` David Hildenbrand
2020-02-05  9:26       ` Wei Yang
2019-10-06  8:56 ` [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span() David Hildenbrand
2020-02-04  9:13   ` Oscar Salvador
2020-02-04  9:20     ` David Hildenbrand
2020-02-04 14:25   ` Baoquan He
2020-02-04 14:42     ` David Hildenbrand
2020-02-05 12:43       ` Baoquan He
2020-02-05 13:20         ` David Hildenbrand
2020-02-05 13:34           ` Baoquan He
2020-02-05 13:38             ` David Hildenbrand
2020-02-05 14:12               ` Baoquan He
2020-02-05 14:16                 ` David Hildenbrand
2020-02-05 14:26                   ` Baoquan He
2020-02-05  9:59   ` Wei Yang
2020-02-05 14:48     ` Baoquan He
2020-02-05 22:56       ` Wei Yang
2020-02-05 23:08         ` Baoquan He
2020-02-05 23:26           ` Wei Yang
2020-02-05 23:30             ` Baoquan He
2020-02-05 23:34               ` Wei Yang
2020-02-05 14:54     ` David Laight
2020-02-05 14:55       ` David Hildenbrand
2019-10-06  8:56 ` [PATCH v6 09/10] mm/memory_hotplug: Drop local variables " David Hildenbrand
2020-02-04  9:26   ` Oscar Salvador
2020-02-04  9:29     ` David Hildenbrand
2020-02-05 10:07   ` Wei Yang
2019-10-06  8:56 ` [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages() David Hildenbrand
2020-02-04  9:46   ` Oscar Salvador
2020-02-04 12:41     ` David Hildenbrand
2020-02-04 13:13       ` Segher Boessenkool
2020-02-04 13:38         ` David Hildenbrand
2020-02-05 12:51           ` Segher Boessenkool
2020-02-05 13:17             ` David Hildenbrand [this message]
2020-02-05 13:18               ` David Hildenbrand
2020-02-05 13:23                 ` David Hildenbrand
2020-02-05 11:48   ` Wei Yang
2019-12-02  9:09 ` [PATCH v6 00/10] mm/memory_hotplug: Shrink zones before removing memory David Hildenbrand
2019-12-03 13:36   ` Oscar Salvador
2020-01-31  4:40     ` Andrew Morton
2020-01-31  9:18       ` David Hildenbrand
2020-01-31 10:03         ` Michal Hocko
2020-01-31 10:36           ` David Hildenbrand
2020-02-04  1:46         ` Andrew Morton
2020-02-04  8:45           ` David Hildenbrand
2020-02-04  9:51             ` Oscar Salvador

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