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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id p79-20020a0de652000000b00573a2a0808esm2002459ywe.77.2023.06.27.13.25.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jun 2023 13:25:55 -0700 (PDT) Date: Tue, 27 Jun 2023 13:25:52 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Matthew Wilcox cc: Hugh Dickins , "Vishal Moola (Oracle)" , Andrew Morton , linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Catalin Marinas , Huacai Chen , Geert Uytterhoeven , Thomas Bogendoerfer , Dinh Nguyen , Jonas Bonn , David Hildenbrand , Claudio Imbrenda , Paul Walmsley , "David S. Miller" , Richard Weinberger , Yoshinori Sato , Dave Hansen , Arnd Bergmann , Christophe Leroy Subject: Re: [PATCH v6 00/33] Split ptdesc from struct page In-Reply-To: Message-ID: <8f1f3dd-50a-3726-87f2-b66d35804ba7@google.com> References: <20230627031431.29653-1-vishal.moola@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On Tue, 27 Jun 2023, Matthew Wilcox wrote: > On Mon, Jun 26, 2023 at 09:44:08PM -0700, Hugh Dickins wrote: > > On Mon, 26 Jun 2023, Vishal Moola (Oracle) wrote: > > > > > The MM subsystem is trying to shrink struct page. This patchset > > > introduces a memory descriptor for page table tracking - struct ptdesc. > > ... > > > 39 files changed, 686 insertions(+), 455 deletions(-) > > > > I don't see the point of this patchset: to me it is just obfuscation of > > the present-day tight relationship between page table and struct page. > > > > Matthew already explained: > > > > > The intent is to get ptdescs to be dynamically allocated at some point > > > in the ~2-3 years out future when we have finished the folio project ... > > > > So in a kindly mood, I'd say that this patchset is ahead of its time. > > But I can certainly adapt to it, if everyone else sees some point to it. > > If you think this patchset is ahead of its time, we can certainly put > it on hold. We're certainly prepared to redo it to be merged after your > current patch series. Thank you, but I can adapt. That was not my point: I'm claiming this patchset is ~2-3 years ahead of its time. > > I think you can see the advantage of the destination, so I don't think > you're against that. Maybe - I have some scepticism, but I'll be happy for that to be dissolved. > Are you opposed to the sequencing of the work to > get us there? I'd be happy to discuss another way to do it. Yes, I'm opposed to churn for no benefit. > > For example, we could dynamically allocate ptdescs right now. We'd get > the benefit of having an arbitrary amount of space in the ptdesc, > although not the benefit of a smaller memmap until everything else is > also dynamically allocated. That sounded much better, at first: churn serving good purpose. But now I suspect you're offering to dynamically allocate a ptdesc, in addition to the struct page of the page table(s) itself, which will be wasted: more memory consumption to no advantage. If that's so, no thanks. Hugh