linux-kernel - Re: [v11 PATCH 3/3] mm: unmap VM_PFNMAP mappings with optimized path

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Message-ID: <889734e0-d2a9-3191-8d48-5c95bf29fb3f@suse.cz>
Date:   Wed, 26 Sep 2018 13:11:45 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <yang.shi@...ux.alibaba.com>, mhocko@...nel.org,
        willy@...radead.org, ldufour@...ux.vnet.ibm.com,
        kirill@...temov.name, akpm@...ux-foundation.org
Cc:     dave.hansen@...el.com, oleg@...hat.com, srikar@...ux.vnet.ibm.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v11 PATCH 3/3] mm: unmap VM_PFNMAP mappings with optimized path

On 9/19/18 7:03 PM, Yang Shi wrote:
> When unmapping VM_PFNMAP mappings, vm flags need to be updated. Since
> the vmas have been detached, so it sounds safe to update vm flags with
> read mmap_sem.
> 
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Reviewed-by: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> ---
>  mm/mmap.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 490340e..847a17d 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2771,15 +2771,6 @@ static int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
>  				munlock_vma_pages_all(tmp);
>  			}
>  
> -			/*
> -			 * Unmapping vmas, which have VM_HUGETLB or VM_PFNMAP,

Ah, the comment should have been already updated with the previous
patch. But nevermind as that all goes away.

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> -			 * need get done with write mmap_sem held since they may
> -			 * update vm_flags.
> -			 */
> -			if (downgrade &&
> -			    (tmp->vm_flags & VM_PFNMAP))
> -				downgrade = false;
> -
>  			tmp = tmp->vm_next;
>  		}
>  	}
>