linux-kernel - Re: [PATCH 1/2] mm: remove redundant check in page_vma_mapped

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Date:   Tue, 4 Jul 2023 10:05:48 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kemeng Shi <shikemeng@...weicloud.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: remove redundant check in page_vma_mapped_walk

On Wed,  5 Jul 2023 05:39:31 +0800 Kemeng Shi <shikemeng@...weicloud.com> wrote:

> For PVMW_SYNC case, we always take pte lock when get first pte of
> PTE-mapped THP in map_pte and hold it until:
> 1. scan of pmd range finished or
> 2. scan of user input range finished or
> 3. user stop walk with page_vma_mapped_walk_done.
> In each case. pte lock will not be freed during middle scan of PTE-mapped
> THP.
> 
> ...
>
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -275,10 +275,6 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>  				goto restart;
>  			}
>  			pvmw->pte++;
> -			if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
> -				pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
> -				spin_lock(pvmw->ptl);
> -			}
>  		} while (pte_none(*pvmw->pte));
>  
>  		if (!pvmw->ptl) {

This code has changed significantly since 6.4.  Please develop against
the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm, thanks.