[RFC PATCH 08/15] fs: proc: use PAGES_PER_SECTION for page offline checking period.

[RFC PATCH 08/15] fs: proc: use PAGES_PER_SECTION for page offline checking period.

[Zi Yan]

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 == 0) {
+		if (page_offline_frozen++ % PAGES_PER_SECTION == 0) {
 			page_offline_thaw();
 			cond_resched();
 			page_offline_freeze();
-- 
2.30.2

Re: [RFC PATCH 08/15] fs: proc: use PAGES_PER_SECTION for page offline checking period.

[Mike Rapoport]

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 == 0) {
> +		if (page_offline_frozen++ % PAGES_PER_SECTION == 0) {

The behavior changes here. E.g. with default configuration on x86 instead
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.

>  			page_offline_thaw();
>  			cond_resched();
>  			page_offline_freeze();
> -- 
> 2.30.2
> 

-- 
Sincerely yours,
Mike.

Re: [RFC PATCH 08/15] proc: use PAGES_PER_SECTION for page offline checking period.

[Zi Yan]

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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 == 0) {
>> +		if (page_offline_frozen++ % PAGES_PER_SECTION == 0) {
>
> The behavior changes here. E.g. with default configuration on x86 instead
> 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 pageblock_nr_pages
to replace MAX_ORDER in this and other patches. pageblock_nr_pages will be unchanged,
so at least in x86_64, using pageblock_nr_pages would not change code behaviors.

—
Best Regards,
Yan, Zi

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