linux-kernel - Re: [PATCH] mm, page_alloc: Fix has_unmovable

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Date:   Mon, 17 Dec 2018 16:34:48 +0100
From:   osalvador@...e.de
To:     Michal Hocko <mhocko@...nel.org>
Cc:     akpm@...ux-foundation.org, vbabka@...e.cz, rppt@...ux.vnet.ibm.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        owner-linux-mm@...ck.org
Subject: Re: [PATCH] mm, page_alloc: Fix has_unmovable_pages for HugePages

On 2018-12-17 16:29, Michal Hocko wrote:
> On Mon 17-12-18 16:06:51, Oscar Salvador wrote:
> [...]
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index a6e7bfd18cde..18d41e85f672 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -8038,11 +8038,12 @@ bool has_unmovable_pages(struct zone *zone, 
>> struct page *page, int count,
>>  		 * handle each tail page individually in migration.
>>  		 */
>>  		if (PageHuge(page)) {
>> +			struct page *head = compound_head(page);
>> 
>> -			if (!hugepage_migration_supported(page_hstate(page)))
>> +			if (!hugepage_migration_supported(page_hstate(head)))
>>  				goto unmovable;
> 
> OK, this makes sense.
> 
>> 
>> -			iter = round_up(iter + 1, 1<<compound_order(page)) - 1;
>> +			iter = round_up(iter + 1, 1<<compound_order(head)) - 1;
> 
> but this less so. You surely do not want to move by the full hugetlb
> page when you got a tail page, right? You could skip too much. You have
> to consider page - head into the equation.

Argh, you're quite right.
I will amend it in the next version.