lkml.org 
[lkml]   [2018]   [Dec]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] mm, page_alloc: Fix has_unmovable_pages for HugePages
On Thu, Dec 20, 2018 at 03:21:27PM +0100, Oscar Salvador wrote:
>On Thu, Dec 20, 2018 at 02:41:32PM +0100, Oscar Salvador wrote:
>> On Thu, Dec 20, 2018 at 02:06:06PM +0100, Michal Hocko wrote:
>> > You did want iter += skip_pages - 1 here right?
>>
>> Bleh, yeah.
>> I am taking vacation today so my brain has left me hours ago, sorry.
>> Should be:
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 4812287e56a0..0634fbdef078 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -8094,7 +8094,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>> goto unmovable;
>>
>> skip_pages = (1 << compound_order(head)) - (page - head);
>> - iter = round_up(iter + 1, skip_pages) - 1;
>> + iter += skip_pages - 1;
>> continue;
>> }
>
>On a second thought, I think it should not really matter.
>
>AFAICS, we can have these scenarios:
>
>1) the head page is the first page in the pabeblock
>2) first page in the pageblock is not a head but part of a hugepage
>3) the head is somewhere within the pageblock
>
>For cases 1) and 3), iter will just get the right value and we will
>break the loop afterwards.
>
>In case 2), iter will be set to a value to skip over the remaining pages.
>
>I am assuming that hugepages are allocated and packed together.
>
>Note that I am not against the change, but I just wanted to see if there is
>something I am missing.

I have another way of classification.

First is three cases of expected new_iter.

1 2 3
v v v
HugePage +-----------------------------------+
^
|
new_iter

From this char, we may have three cases:

1) iter is the head page
2) iter is the middle page
2) iter is the tail page

No matter which case iter starts, new_iter should be point to tail + 1.

Second is the relationship between the new_iter and the pageblock, only
two cases:

1) new_iter is still in current pageblock
2) new_iter is out of current pageblock

For both cases, current loop handles it well.

Now let's go back to see how to calculate new_iter. From the chart
above, we can see this formula stands for all three cases:

new_iter = round_up(iter + 1, page_size(HugePage))

So it looks the first version is correct.

>--
>Oscar Salvador
>SUSE L3

--
Wei Yang
Help you, Help me

\
 
 \ /
  Last update: 2018-12-20 16:33    [W:0.081 / U:1.768 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site