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

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Date:   Wed, 17 Aug 2022 10:34:12 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Haiyue Wang <haiyue.wang@...el.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
CC:     <akpm@...ux-foundation.org>, <david@...hat.com>,
        <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 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.

Thanks,
Miaohe Lin