linux-kernel - Re: [PATCH v6 2/2] mm: fix the handling Non-LRU pages returned by follow

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Date:   Tue, 23 Aug 2022 12:07:04 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>,
        Haiyue Wang <haiyue.wang@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org, apopple@...dia.com,
        ying.huang@...el.com, songmuchun@...edance.com,
        naoya.horiguchi@...ux.dev, alex.sierra@....com,
        Felix Kuehling <Felix.Kuehling@....com>
Subject: Re: [PATCH v6 2/2] mm: fix the handling Non-LRU pages returned by
 follow_page

On 17.08.22 04:34, Miaohe Lin wrote:
> On 2022/8/16 10:21, Haiyue Wang wrote:
>> The handling Non-LRU pages returned by follow_page() jumps directly, it
>> doesn't call put_page() to handle the reference count, since 'FOLL_GET'
>> flag for follow_page() has get_page() called. Fix the zone device page
>> check by handling the page reference count correctly before returning.
>>
>> And as David reviewed, "device pages are never PageKsm pages". Drop this
>> zone device page check for break_ksm().
>>
>> Fixes: 3218f8712d6b ("mm: handling Non-LRU pages returned by vm_normal_pages")
>> Signed-off-by: Haiyue Wang <haiyue.wang@...el.com>
>> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
>> Reviewed-by: Felix Kuehling <Felix.Kuehling@....com>
> 
> Thanks for your fixing. LGTM with one nit below. But I have no strong opinion on it.
> So with or without fixing below nit:
> 
> Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>
> 
>> ---
>>  mm/huge_memory.c |  4 ++--
>>  mm/ksm.c         | 12 +++++++++---
>>  mm/migrate.c     | 19 ++++++++++++-------
>>  3 files changed, 23 insertions(+), 12 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 8a7c1b344abe..b2ba17c3dcd7 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2963,10 +2963,10 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
>>  		/* FOLL_DUMP to ignore special (like zero) pages */
>>  		page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
>>  
>> -		if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
>> +		if (IS_ERR_OR_NULL(page))
>>  			continue;
>>  
>> -		if (!is_transparent_hugepage(page))
>> +		if (is_zone_device_page(page) || !is_transparent_hugepage(page))
> 
> !is_transparent_hugepage should already do the work here? IIRC, zone_device_page can't be
> a transhuge page anyway. And only transparent_hugepage is cared here.

I agree.

Can we avoid sending a new version of a patch series as reply to another
patch series (previous version)?


Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb