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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id bi36-20020a05620a31a400b0078d677e72f3sm1195367qkb.118.2024.04.11.09.15.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Apr 2024 09:15:38 -0700 (PDT) Date: Thu, 11 Apr 2024 12:15:36 -0400 From: Peter Xu To: Jason Gunthorpe , Christophe Leroy Cc: Christophe Leroy , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [RFC PATCH 0/8] Reimplement huge pages without hugepd on powerpc 8xx Message-ID: References: <20240325163840.GF6245@nvidia.com> MIME-Version: 1.0 In-Reply-To: <20240325163840.GF6245@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Stat-Signature: 74rk4jabjknb4d8bsu5zm6ngkxxpe1rt X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 245EE40011 X-HE-Tag: 1712852142-908909 X-HE-Meta: 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 wxBzVC9c tqr5wC8d4CHZFrh7SwKFyCCtv2dVjjuk5lwQ65mtisneSf4mJmBYsXzRugKGU2EqssgQNM+WIsoYbcu5/iik9i7RYMCwMXiCY/DoMJHaq6wcnWyFwna4Rl2dBz1uCQhOj2cE5tE6/SKAHBsd8cJVlWNSOjVPJc3VmHDKsq6ARykMnRmg5NzztEBDbI6RnI1ZptK/JkZyT4dP+qAoxPSHDICAByk9g1ga5G2tndzeL7zI9fbvRwYJLz99VAJo5I+Vby6uRST5jie7E+4t4NQACjOXap8s822CaiGmUGF0KRCK4x7rMKFS6q4TGrnL44onmSwhX3N4zKcWOX149wabVcLxEcGC8Mcp64fEM5XuqzcvsHvg= 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 Mon, Mar 25, 2024 at 01:38:40PM -0300, Jason Gunthorpe wrote: > On Mon, Mar 25, 2024 at 03:55:53PM +0100, Christophe Leroy wrote: > > This series reimplements hugepages with hugepd on powerpc 8xx. > > > > Unlike most architectures, powerpc 8xx HW requires a two-level > > pagetable topology for all page sizes. So a leaf PMD-contig approach > > is not feasible as such. > > > > Possible sizes are 4k, 16k, 512k and 8M. > > > > First level (PGD/PMD) covers 4M per entry. For 8M pages, two PMD entries > > must point to a single entry level-2 page table. Until now that was > > done using hugepd. This series changes it to use standard page tables > > where the entry is replicated 1024 times on each of the two pagetables > > refered by the two associated PMD entries for that 8M page. > > > > At the moment it has to look into each helper to know if the > > hugepage ptep is a PTE or a PMD in order to know it is a 8M page or > > a lower size. I hope this can me handled by core-mm in the future. > > > > There are probably several ways to implement stuff, so feedback is > > very welcome. > > I thought it looks pretty good! I second it. I saw the discussions in patch 1. Christophe, I suppose you're exploring the big hammer over hugepd, and perhaps went already with the 32bit pmd solution for nohash/32bit challenge you mentioned? I'm trying to position my next step; it seems like at least I should not adding any more hugepd code, then should I go with ARCH_HAS_HUGEPD checks, or you're going to have an RFC soon then I can base on top? Thanks, -- Peter Xu