From: Yajun Deng <yajun.deng@linux.dev>
To: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, vbabka@suse.cz, lstoakes@gmail.com
Subject: Re: [PATCH] mm/mmap: remove the mm parameter in vma_complete()
Date: Thu, 22 Feb 2024 18:26:18 +0800 [thread overview]
Message-ID: <7229eb6e-bf3e-fa97-6709-6c92bc72443b@linux.dev> (raw)
In-Reply-To: <20240129150417.3m6jyj3ftdh6ka7x@revolver>
Adding Vlastimil and Lorenzo to discuss this patch.
On 2024/1/29 23:04, Liam R. Howlett wrote:
> * Yajun Deng <yajun.deng@linux.dev> [240129 02:53]:
>> There are vma_merge() and do_brk_flags() pass mm to vma_complete(), others
>> would pass the vma->vm_mm. The following explains that the mm is the
>> vma->vm_mm in vma_merge() and do_brk_flags().
>>
>> All vma will point to the same mm struct if the vma_merge() is successful.
>> So the mm and the vma->mm are the same.
> Absolutely, they must be the same. I don't think vma_merge() checks
> this, but it is true.
>
>> vm_brk_flags() and brk syscall will initialize vmi with current->mm,
>> so the vma->vm_mm and the current->mm are the same if vma exists in
>> do_brk_flags().
>>
>> Remove the mm parameter in vma_complete() and get mm from the vma in vp.
> You have added a dereference to the two paths that don't need it to
> reduce the argument list from 3 to 2. It's the same number of lines as
> well. vma_shrink() is only used on process creation, but brk is more
> common. Note that this function is marked as inline.
>
> I'm not sure this change is worth making.
If we can make sure the mm is vma->vm_mm, I don't think we need to pass
the mm.
If we can't make sure that, this change is not worth it.
>> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
>> ---
>> mm/mmap.c | 16 ++++++++--------
>> 1 file changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index e97b9144c61a..9b968d1edf55 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -509,11 +509,11 @@ static inline void vma_prepare(struct vma_prepare *vp)
>> *
>> * @vp: The vma_prepare struct
>> * @vmi: The vma iterator
>> - * @mm: The mm_struct
>> */
>> -static inline void vma_complete(struct vma_prepare *vp,
>> - struct vma_iterator *vmi, struct mm_struct *mm)
>> +static inline void vma_complete(struct vma_prepare *vp, struct vma_iterator *vmi)
>> {
>> + struct mm_struct *mm = vp->vma->vm_mm;
>> +
>> if (vp->file) {
>> if (vp->adj_next)
>> vma_interval_tree_insert(vp->adj_next,
>> @@ -666,7 +666,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
>> vma_set_range(vma, start, end, pgoff);
>> vma_iter_store(vmi, vma);
>>
>> - vma_complete(&vp, vmi, vma->vm_mm);
>> + vma_complete(&vp, vmi);
>> return 0;
>>
>> nomem:
>> @@ -707,7 +707,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
>>
>> vma_iter_clear(vmi);
>> vma_set_range(vma, start, end, pgoff);
>> - vma_complete(&vp, vmi, vma->vm_mm);
>> + vma_complete(&vp, vmi);
>> return 0;
>> }
>>
>> @@ -1030,7 +1030,7 @@ static struct vm_area_struct
>> }
>> }
>>
>> - vma_complete(&vp, vmi, mm);
>> + vma_complete(&vp, vmi);
>> khugepaged_enter_vma(res, vm_flags);
>> return res;
>>
>> @@ -2377,7 +2377,7 @@ static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
>> }
>>
>> /* vma_complete stores the new vma */
>> - vma_complete(&vp, vmi, vma->vm_mm);
>> + vma_complete(&vp, vmi);
>>
>> /* Success. */
>> if (new_below)
>> @@ -3145,7 +3145,7 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
>> vm_flags_set(vma, VM_SOFTDIRTY);
>> vma_iter_store(vmi, vma);
>>
>> - vma_complete(&vp, vmi, mm);
>> + vma_complete(&vp, vmi);
>> khugepaged_enter_vma(vma, flags);
>> goto out;
>> }
>> --
>> 2.25.1
>>
>>
next prev parent reply other threads:[~2024-02-22 10:26 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-29 7:53 [PATCH] mm/mmap: remove the mm parameter in vma_complete() Yajun Deng
2024-01-29 15:04 ` Liam R. Howlett
2024-02-22 10:26 ` Yajun Deng [this message]
2024-02-22 16:22 ` Liam R. Howlett
2024-02-23 2:36 ` Yajun Deng
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