linux-kernel - Re: [PATCH v1 3/6] mm/page_isolation: drop WARN_ON_ONCE() in set_migratetype

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Message-ID: <c292099c-1275-747e-6697-bc3cfda47e79@redhat.com>
Date:   Wed, 29 Jul 2020 15:37:00 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S . Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v1 3/6] mm/page_isolation: drop WARN_ON_ONCE() in
 set_migratetype_isolate()

On 29.07.20 15:24, Baoquan He wrote:
> On 06/30/20 at 04:26pm, David Hildenbrand wrote:
>> Inside has_unmovable_pages(), we have a comment describing how unmovable
>> data could end up in ZONE_MOVABLE - via "movable_core". Also, besides
> 					  ~~~ 'movablecore'
>> checking if the first page in the pageblock is reserved, we don't
>> perform any further checks in case of ZONE_MOVABLE.
>>
>> In case of memory offlining, we set REPORT_FAILURE, properly
>> dump_page() the page and handle the error gracefully.
>> alloc_contig_pages() users currently never allocate from ZONE_MOVABLE.
>> E.g., hugetlb uses alloc_contig_pages() for the allocation of gigantic
>> pages only, which will never end up on the MOVABLE zone
>> (see htlb_alloc_mask()).
>>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: Michael S. Tsirkin <mst@...hat.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>  mm/page_isolation.c | 16 ++++++----------
>>  1 file changed, 6 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index 553b49a34cf71..02a01bff6b219 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -58,16 +58,12 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>>  	spin_unlock_irqrestore(&zone->lock, flags);
>>  	if (!ret) {
>>  		drain_all_pages(zone);
>> -	} else {
>> -		WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
>> -
>> -		if ((isol_flags & REPORT_FAILURE) && unmovable)
>> -			/*
>> -			 * printk() with zone->lock held will likely trigger a
>> -			 * lockdep splat, so defer it here.
>> -			 */
>> -			dump_page(unmovable, "unmovable page");
>> -	}
>> +	} else if ((isol_flags & REPORT_FAILURE) && unmovable)
> 
> This else if branch should be enclosed in brace?
> 

Not necessarily. And it will be gone in the next patch in this series :)

Thanks!


-- 
Thanks,

David / dhildenb