linux-kernel - Re: [PATCH v4 04/11] mm/hugetlb: make hugetlb migration callback CMA aware

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Message-ID: <87h7uil1f7.fsf@linux.ibm.com>
Date:   Wed, 08 Jul 2020 16:27:16 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
        Joonsoo Kim <js1304@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 04/11] mm/hugetlb: make hugetlb migration callback
 CMA aware

Vlastimil Babka <vbabka@...e.cz> writes:

> On 7/8/20 9:41 AM, Michal Hocko wrote:
>> On Wed 08-07-20 16:16:02, Joonsoo Kim wrote:
>>> On Tue, Jul 07, 2020 at 01:22:31PM +0200, Vlastimil Babka wrote:
>>> 
>>> Simply, I call memalloc_nocma_{save,restore} in new_non_cma_page(). It
>>> would not cause any problem.
>> 
>> I believe a proper fix is the following. The scope is really defined for
>> FOLL_LONGTERM pins and pushing it inside check_and_migrate_cma_pages
>> will solve the problem as well but it imho makes more sense to do it in
>> the caller the same way we do for any others. 
>> 
>> Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region")
>
> Agreed.
>
>> 
>> I am not sure this is worth backporting to stable yet.
>
> CC Aneesh.
>
> Context: since check_and_migrate_cma_pages() calls __get_user_pages_locked(), it
> should also be called under memalloc_nocma_save().

But by then we faulted in all relevant pages and migrated them out of
CMA rea right?


>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index de9e36262ccb..75980dd5a2fc 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1794,7 +1794,6 @@ static long __gup_longterm_locked(struct task_struct *tsk,
>>  				     vmas_tmp, NULL, gup_flags);
>>  
>>  	if (gup_flags & FOLL_LONGTERM) {
>> -		memalloc_nocma_restore(flags);
>>  		if (rc < 0)
>>  			goto out;
>>  
>> @@ -1802,11 +1801,13 @@ static long __gup_longterm_locked(struct task_struct *tsk,
>>  			for (i = 0; i < rc; i++)
>>  				put_page(pages[i]);
>>  			rc = -EOPNOTSUPP;
>> +			memalloc_nocma_restore(flags);
>>  			goto out;
>>  		}
>>  
>>  		rc = check_and_migrate_cma_pages(tsk, mm, start, rc, pages,
>>  						 vmas_tmp, gup_flags);
>> +		memalloc_nocma_restore(flags);
>>  	}
>>  
>>  out:
>> 

-aneesh