linux-kernel - Re: [PATCH 2/2] mm: add pageblock

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Message-ID: <9ab7d4b4-505b-0532-09fd-186814b7fc8f@huawei.com>
Date:   Fri, 2 Sep 2022 17:39:43 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>
CC:     Mike Rapoport <rppt@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        <linux-kernel@...r.kernel.org>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 2/2] mm: add pageblock_aligned() macro


On 2022/9/2 17:04, David Hildenbrand wrote:
> On 02.09.22 11:02, Kefeng Wang wrote:
>> On 2022/9/2 16:42, David Hildenbrand wrote:
>>> On 02.09.22 08:47, Kefeng Wang wrote:
>>>> Add pageblock_aligned() and use it to simplify code.
>>>>
>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>>>> ---
>>> [...]
>>>
>>>> -	unsigned long nr_pgmask = pageblock_nr_pages - 1;
>>>>   	int nid = zone_to_nid(zone);
>>>>   	unsigned long nr_pages = 0;
>>>>   	int zid = zone_idx(zone);
>>>> @@ -1977,7 +1974,7 @@ static unsigned long  __init deferred_init_pages(struct zone *zone,
>>>>   		if (!deferred_pfn_valid(pfn)) {
>>>>   			page = NULL;
>>>>   			continue;
>>>> -		} else if (!page || !(pfn & nr_pgmask)) {
>>> I didn't sleep too well this night and am tired, please tell me why I'm
>>> wrong :)
>> Wish you have a good reset :)
> Thanks, the headache isn't helping :D
>
>>> "pfn & (pageblock_nr_pages - 1)" is true if the pageblock is not aligned
>>>
>>> E.g., pfn = 1, pageblock_nr_pages = 512
>>>
>>> pfn & (pageblock_nr_pages - 1)
>>> -> 1 & (512 - 1)
>>> -> 1 & 511
>>> -> true
>>>
>>> "!(pfn & (pageblock_nr_pages - 1))" is true if the pageblock is aligned
>>> -> !(true)
>>> -> false
>>>
>>>
>>> However, "!pageblock_aligned(1)" = true
>>>
>>>
>>>> +		} else if (!page || !pageblock_aligned(pfn)) {
>> pageblock_aligned(pfn) IS_ALIGNED((unsigned long)(pfn), pageblock_nr_pages)
>>
>> #define IS_ALIGNED(x, a) (((x) & ((typeof(x))(a) - 1)) == 0) (((pfn) &
>> (pageblock_nr_pages - 1)) == 0) -> ((1 & 512 -1) == 0) -> ((1 & 511) ==
>> 0) -> ((511) == 0) -> false
>> right ?
> yes ... and inverting that would give you "true", which is not what we want?
>
oops...  it's my fault, looks like I need to have a reset to save my 
brain...
> Again, sorry if I'm wrong ...
>