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From:   Zi Yan <ziy@nvidia.com>
To:     Mike Rapoport <rppt@kernel.org>
Cc:     David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Michal Hocko <mhocko@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        linux-kernel@vger.kernel.org, Oscar Salvador <osalvador@suse.de>,
        Ying Chen <chenying.kernel@bytedance.com>,
        Feng Zhou <zhoufeng.zf@bytedance.com>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH 08/15] proc: use PAGES_PER_SECTION for page offline checking period.
Date:   Mon, 09 Aug 2021 11:45:27 -0400
Message-ID: <BB81E5C9-D796-4952-B4F7-E966FB74EE78@nvidia.com>
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References: <20210805190253.2795604-1-zi.yan@sent.com>
 <20210805190253.2795604-9-zi.yan@sent.com> <YQ5hIFZX02BMS+Yb@kernel.org>
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On 7 Aug 2021, at 6:32, Mike Rapoport wrote:

> On Thu, Aug 05, 2021 at 03:02:46PM -0400, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>>
>> It keeps the existing behavior after MAX_ORDER is increased beyond
>> a section size.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> Cc: Mike Rapoport <rppt@kernel.org>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Ying Chen <chenying.kernel@bytedance.com>
>> Cc: Feng Zhou <zhoufeng.zf@bytedance.com>
>> Cc: linux-fsdevel@vger.kernel.org
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.kernel.org
>> ---
>>  fs/proc/kcore.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
>> index 3f148759a5fd..77b7ba48fb44 100644
>> --- a/fs/proc/kcore.c
>> +++ b/fs/proc/kcore.c
>> @@ -486,7 +486,7 @@ read_kcore(struct file *file, char __user *buffer,=
 size_t buflen, loff_t *fpos)
>>  			}
>>  		}
>>
>> -		if (page_offline_frozen++ % MAX_ORDER_NR_PAGES =3D=3D 0) {
>> +		if (page_offline_frozen++ % PAGES_PER_SECTION =3D=3D 0) {
>
> The behavior changes here. E.g. with default configuration on x86 inste=
ad
> of cond_resched() every 2M we get cond_resched() every 128M.
>
> I'm not saying it's wrong but at least it deserves an explanation why.

Sure. I will also think about whether I should use PAGES_PER_SECTION or p=
ageblock_nr_pages
to replace MAX_ORDER in this and other patches. pageblock_nr_pages will b=
e unchanged,
so at least in x86_64, using pageblock_nr_pages would not change code beh=
aviors.

=E2=80=94
Best Regards,
Yan, Zi

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