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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 X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: BF6301C0013 X-Stat-Signature: ahwkbcwxsxbrzounbjr1o87pdinh5sii X-Rspam-User: X-HE-Tag: 1687897556-969332 X-HE-Meta: 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 ML3jtmeZ OqVSnhJTBX0R1E2CCamQbU5pRKn1zc0efxQAx40I6vcs5EbImT2EN5hrqAnmFEYku+0YZQQH8VsTXcs4xue2DeN5g1ccMtUGU87ksimkjezO/QWDAbzVlmJbJ5RtGVY1bbQo0ffPLBLk6WRdhS2Xynm2k3YJubvX3HpFwDBFPsyrmKmUXqdS440yOswcx/Ju8E7K9p3LBcMi2LSJLlIl+UUHXqzKJ1tuXLlyk/E3aXaA7gJ61/PSQFfS45O2jZwk7AyYdi19tY7HkV/evgvR8UXdZ/jhZxg00U3xgOomC4Q8CHPchFjweioXxIjbiLan/rA4ELoKQyx508KBjK9uPQ5lK1GzmnoXRdy0KiI9pnd/IozmpWd1Yt5JB2amp1ZXocUl+MqULbWaaxo0dCHZwxKzW1jutxyeUippYFY9dRKdH8jHQZCYhenB1YQ== 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 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