linux-kernel - Re: [PATCH 2/2] [PATCH 2/2] mm: add merging after mremap resize

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Date:   Sat, 28 May 2022 02:46:57 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Jakub Matěna <matenajakub@...il.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
        vbabka@...e.cz, mhocko@...nel.org, mgorman@...hsingularity.net,
        willy@...radead.org, liam.howlett@...cle.com, hughd@...gle.com,
        riel@...riel.com, rostedt@...dmis.org, peterz@...radead.org
Subject: Re: [PATCH 2/2] [PATCH 2/2] mm: add merging after mremap resize

On Fri, May 27, 2022 at 12:48:10PM +0200, Jakub Matěna wrote:
> When mremap call results in expansion, it might be possible to merge the
> VMA with the next VMA which might become adjacent. This patch adds
> vma_merge call after the expansion is done to try and merge.
> 
> Signed-off-by: Jakub Matěna <matenajakub@...il.com>
> ---
>  mm/mremap.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 303d3290b938..c41237e62156 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -9,6 +9,7 @@
>   */
>  
>  #include <linux/mm.h>
> +#include <linux/mm_inline.h>
>  #include <linux/hugetlb.h>
>  #include <linux/shm.h>
>  #include <linux/ksm.h>
> @@ -1022,8 +1023,11 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
>  				}
>  			}
>  
> -			if (vma_adjust(vma, vma->vm_start, addr + new_len,
> -				       vma->vm_pgoff, NULL)) {
> +			vma = vma_merge(mm, vma, addr + old_len, addr + new_len,
> +					vma->vm_flags, vma->anon_vma, vma->vm_file,
> +					vma->vm_pgoff + (old_len >> PAGE_SHIFT), vma_policy(vma),
> +					vma->vm_userfaultfd_ctx, anon_vma_name(vma));

The arguement list gets busy. Maybe some variables would help.
Calculation around vm_pgoff is not obvious and requires some explanation.

> +			if (!vma) {
>  				vm_unacct_memory(pages);
>  				ret = -ENOMEM;
>  				goto out;
> -- 
> 2.35.1
> 

-- 
 Kirill A. Shutemov