linux-kernel - Re: [PATCH v4 27/66] mm/mmap: Change do_brk_munmap() to use do_mas_align

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Date:   Tue, 18 Jan 2022 12:57:41 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Liam Howlett <liam.howlett@...cle.com>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 27/66] mm/mmap: Change do_brk_munmap() to use
 do_mas_align_munmap()

On 12/1/21 15:30, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> 
> do_brk_munmap() has already aligned the address and has a maple tree
> state to be used.  Use the new do_mas_align_munmap() to avoid
> unnecessary alignment and error checks.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
>  mm/mmap.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 14190306a483..79b8494d83c6 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2926,12 +2926,15 @@ static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
>  	struct mm_struct *mm = vma->vm_mm;
>  	struct vm_area_struct unmap;
>  	unsigned long unmap_pages;
> -	int ret = 1;
> +	int ret;
>  
>  	arch_unmap(mm, newbrk, oldbrk);
>  
> -	if (likely(vma->vm_start >= newbrk)) { // remove entire mapping(s)
> -		ret = do_mas_munmap(mas, mm, newbrk, oldbrk-newbrk, uf, true);
> +	if (likely((vma->vm_end < oldbrk) ||
> +		   ((vma->vm_start == newbrk) && (vma->vm_end == oldbrk)))) {

Can you describe this change of conditions in the commit log as well?

> +		// remove entire mapping(s)
> +		ret = do_mas_align_munmap(mas, vma, mm, newbrk, oldbrk, uf,
> +					  true);
>  		goto munmap_full_vma;
>  	}
>