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
next prev parent 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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