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[67.164.59.41]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-237d860fb63sm139983845ad.130.2025.06.25.12.23.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Jun 2025 12:23:16 -0700 (PDT) Date: Wed, 25 Jun 2025 12:23:13 -0700 From: "Vishal Moola (Oracle)" To: Matthew Wilcox Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Jordan Rome , Andrew Morton Subject: Re: [RFC PATCH 1/3] mm/memory.c: convert __copy_remote_vm_str() to folios Message-ID: References: <20250625174841.1094510-1-vishal.moola@gmail.com> <20250625174841.1094510-2-vishal.moola@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jun 25, 2025 at 07:00:22PM +0100, Matthew Wilcox wrote: > On Wed, Jun 25, 2025 at 10:48:39AM -0700, Vishal Moola (Oracle) wrote: > > +++ b/mm/memory.c > > @@ -6820,9 +6820,10 @@ static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr, > > } > > > > while (len) { > > - int bytes, offset, retval; > > + int bytes, folio_offset, page_offset retval; > > offset_in_folio() returns a size_t so that we can support folios larger > than 2GB (which is a real possibility here; hugetlbfs might end up with > a 16GB folio on some architectures). Got it, I'll change that. > > @@ -6837,17 +6838,20 @@ static int __copy_remote_vm_str(struct mm_struct *mm, unsigned long addr, > > goto out; > > } > > > > + folio = page_folio(page); > > bytes = len; > > - offset = addr & (PAGE_SIZE - 1); > > - if (bytes > PAGE_SIZE - offset) > > - bytes = PAGE_SIZE - offset; > > + folio_offset = offset_in_folio(folio, addr); > > Umm. Not sure this is safe. A folio might be mapped misaligned, so > 'addr' might not give you the right offset within the folio. I think > you might need to use addr - (vma->vm_pgoff << PAGE_SHIFT). But I'd > defer to others here ... particularly when it comes to anonymous folios. Ah ok, I didn't realize folios could be misaligned. I'll play around with your proposed calculation.