linux-kernel - Re: [RFC PATCH v2 01/10] mm/mremap: introduce more mergeable mremap via MREMAP_RELOCATE

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Message-ID: <8c052822-5365-4178-8e06-ecd4f917cf8a@lucifer.local>
Date: Wed, 30 Apr 2025 14:15:24 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>, Pedro Falcato <pfalcato@...e.de>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 01/10] mm/mremap: introduce more mergeable mremap
 via MREMAP_RELOCATE_ANON

On Wed, Apr 30, 2025 at 12:47:03AM +0000, Wei Yang wrote:
> On Tue, Apr 22, 2025 at 09:09:20AM +0100, Lorenzo Stoakes wrote:
> [...]
> >+bool vma_had_uncowed_children(struct vm_area_struct *vma)
> >+{
> >+	struct anon_vma *anon_vma = vma ? vma->anon_vma : NULL;
> >+	bool ret;
> >+
> >+	if (!anon_vma)
> >+		return false;
> >+
> >+	/*
> >+	 * If we're mmap locked then there's no way for this count to change, as
> >+	 * any such change would require this lock not be held.
> >+	 */
> >+	if (rwsem_is_locked(&vma->vm_mm->mmap_lock))
> >+		return anon_vma->num_children > 1;
>
> Hi, Lorenzo
>
> May I have a question here?

Just ask the question.

However, with respect, the last drive-by review you gave was not helpful,
so I strongly suggest that this is not a great use of your time.

Again, I _strongly_ suggest you focus on bug fixes or the like.

Thanks.

>
> >+
> >+	/*
> >+	 * Any change that would increase the number of children would be
> >+	 * prevented by a read lock.
> >+	 */
> >+	anon_vma_lock_read(anon_vma);
> >+	ret = anon_vma->num_children > 1;
> >+	anon_vma_unlock_read(anon_vma);
> >+
> >+	return ret;
> >+}
>
> --
> Wei Yang
> Help you, Help me