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Wed, 30 Apr 2025 08:41:20 -0700 (PDT) Date: Wed, 30 Apr 2025 15:41:19 +0000 From: Wei Yang To: Lorenzo Stoakes Cc: Wei Yang , Andrew Morton , Vlastimil Babka , Jann Horn , "Liam R . Howlett" , Suren Baghdasaryan , Matthew Wilcox , David Hildenbrand , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 01/10] mm/mremap: introduce more mergeable mremap via MREMAP_RELOCATE_ANON Message-ID: <20250430154119.a5ljf5t5tutqzim5@master> Reply-To: Wei Yang References: <87e668d54927bb4ccdb7d374275e0662de667697.1745307301.git.lorenzo.stoakes@oracle.com> <20250430004703.63rumj4znewlbc2h@master> <8c052822-5365-4178-8e06-ecd4f917cf8a@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8c052822-5365-4178-8e06-ecd4f917cf8a@lucifer.local> User-Agent: NeoMutt/20170113 (1.7.2) X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 9C6264000F X-Stat-Signature: e5kde4jdpgpi8bjrrx7krffii4gs6cxk X-HE-Tag: 1746027682-233424 X-HE-Meta: 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 JducJE22 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 30, 2025 at 02:15:24PM +0100, Lorenzo Stoakes wrote: >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. > Thanks. My question is the function is expected to return true, if we have forked a vma from this one, right? IMO there are cases when it has one forked child and anon_vma->num_children == 1, which means folios are not exclusively mapped. But the function would return false. Or maybe I misunderstand the logic here. >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 for your suggestion and patience. I would try to focus on bugs and skip those subtle things. > >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 -- Wei Yang Help you, Help me