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Shutemov" To: Will Deacon Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, Catalin Marinas , Jan Kara , Minchan Kim , Andrew Morton , "Kirill A . Shutemov" , Linus Torvalds , Vinayak Menon , Hugh Dickins , kernel-team@android.com Subject: Re: [PATCH v2 2/3] mm: Allow architectures to request 'old' entries when prefaulting Message-ID: <20210111144713.3akhv75xzk7u6rgu@box> References: <20210108171517.5290-1-will@kernel.org> <20210108171517.5290-3-will@kernel.org> <20210111142533.oulduqd76mkpdkst@box> <20210111143742.GD7642@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210111143742.GD7642@willie-the-truck> 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: On Mon, Jan 11, 2021 at 02:37:42PM +0000, Will Deacon wrote: > On Mon, Jan 11, 2021 at 05:25:33PM +0300, Kirill A. Shutemov wrote: > > On Fri, Jan 08, 2021 at 05:15:16PM +0000, Will Deacon wrote: > > > diff --git a/mm/filemap.c b/mm/filemap.c > > > index c1f2dc89b8a7..0fb9d1714797 100644 > > > --- a/mm/filemap.c > > > +++ b/mm/filemap.c > > > @@ -3051,14 +3051,18 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, > > > if (!pte_none(*vmf->pte)) > > > goto unlock; > > > > > > + /* We're about to handle the fault */ > > > + if (vmf->address == address) { > > > + vmf->flags &= ~FAULT_FLAG_PREFAULT; > > > + ret = VM_FAULT_NOPAGE; > > > + } else { > > > + vmf->flags |= FAULT_FLAG_PREFAULT; > > > + } > > > + > > > > Do we need to restore the oririnal status of the bit once we are done? > > I can certainly add that, although it doesn't look like we do that for > vmf->pte, so it's hard to tell what the rules are here. It certainly feels > odd to restore some fields but not others, as it looks like vmf->address > will be out-of-whack with vmf->pte when filemap_map_pages() returns. Am I > missing something? Unlike vmf->flags or vmf->address, vmf->pte is not going to be reused. finish_fault() will overwrite it. Yeah, it's messy. -- Kirill A. Shutemov