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AJvYcCVSxNMd88AqFeJpJwz3aa4rJM8VkaRMFDprJ3JrPfcnIB4fcFm59WPORTnaBpVxGcierExoFlkB7A==@kvack.org X-Gm-Message-State: AOJu0YxU9LVc/SkyLtochOKlY/y2GbSJXu5hlwF4WDBOycQjS4kGDDOB j9VLbfEaVvd0Kl3uuyEBjPn1koX0jCAfAqZO7gI7QMNvIbIVUowz8KocBZ+RO8kqwpp8C7I5Ed1 EXUzbyf3YUBk/P/MIDE6PXdVJpJkIDd/qfKt0 X-Gm-Gg: ASbGncuf6KcpjQ+1E5kV50Jc+cY86NnXuFT65BE8Dv/JWIQ/vENpg7rrkfXhHDwWIjI FaCpu3iPC8fNItFycbjD7FQpbDOHKR4/5Wxes3HmeyjTtu344NhDtMR0W7iAMEZLJWkRbDvYSZF MFdjeuFhFHB56UfERHUpDZ7cbOydr5AA71d6ATd35rVJk4ZeaRoF5pXWdU X-Google-Smtp-Source: AGHT+IGEYvRnZ220N49P6WowIdeV7ZMLCe1Ohy+RRvGTUY8QE/Mjht3NMEOKTlyUkZYJGE+AY5DQq5bo+Xh81NMJc/8= X-Received: by 2002:a05:622a:1a0d:b0:477:2c12:9253 with SMTP id d75a77b69052e-48aea4670b3mr5562161cf.16.1746127664234; Thu, 01 May 2025 12:27:44 -0700 (PDT) MIME-Version: 1.0 References: <20250501052532.1903125-1-jyescas@google.com> In-Reply-To: From: Juan Yescas Date: Thu, 1 May 2025 12:27:31 -0700 X-Gm-Features: ATxdqUHbSRMwrhBZUMF2ojlrG-8kcb7B4aDa27SXz78tq394QFyw_svY2uWGfzU Message-ID: Subject: Re: [PATCH] mm: Add ARCH_FORCE_PAGE_BLOCK_ORDER to select page block order To: Matthew Wilcox Cc: Catalin Marinas , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, tjmercier@google.com, isaacmanjarres@google.com, surenb@google.com, kaleshsingh@google.com, Vlastimil Babka , "Liam R. Howlett" , Lorenzo Stoakes , David Hildenbrand , Mike Rapoport , Zi Yan , Minchan Kim Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 54037180012 X-Stat-Signature: n5mhp5k5yhsbe1rk9etn71fdsi9ayrcq X-HE-Tag: 1746127665-647934 X-HE-Meta: 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 MPmy2502 UjtX1XNPIMHbE6DmmbxDDW3AD2HmRJELckkfBtYRD9WxDcQiLqetMUXaHk7C/yG7mLMp7xLBaEXyQSxVlbzJ6nw//fICSrpmuxkwYUTT96Z+i+zt1xino5xelIVBuM+iwAs/cEo6D14QBuWQB4IbXwnTfufV2IbBlruNY7WRpJBbuTQ8gbB/YythKD39eh0Q8K9VHjEgSdTBuem7uVTclvrsP7W+YQORwt/NmRMG3Hy1FasmhsNJ/UcDbwvFs8/Kgan+Tpz4mSRsOnoHOrERHG+GfGEfersdF0v9/xVRbRQnokO0= 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 Thu, May 1, 2025 at 11:38=E2=80=AFAM Matthew Wilcox wrote: > > On Wed, Apr 30, 2025 at 10:25:11PM -0700, Juan Yescas wrote: > > Problem: On large page size configurations (16KiB, 64KiB), the CMA > > alignment requirement (CMA_MIN_ALIGNMENT_BYTES) increases considerably, > > and this causes the CMA reservations to be larger than necessary. > > This means that system will have less available MIGRATE_UNMOVABLE and > > MIGRATE_RECLAIMABLE page blocks since MIGRATE_CMA can't fallback to the= m. > > > > The CMA_MIN_ALIGNMENT_BYTES increases because it depends on > > MAX_PAGE_ORDER which depends on ARCH_FORCE_MAX_ORDER. The value of > > ARCH_FORCE_MAX_ORDER increases on 16k and 64k kernels. > > Sure, but why would any architecture *NOT* want to set this? You are right, not all the architectures support large page sizes and don't= have the CMA alignment issues that arm64 with 16k and 64k page sizes have. This change only affects arm64 architectures. > This seems like you're making each architecture bump into the problem > by itself, when the real problem is that the CMA people never thought > about this and should have come up with better defaults. This change will only affect arm64 architectures. By default, ARCH_FORCE_PAGE_BLOCK_ORDER will have the same value that ARCH_FORCE_MAX_ORDER (This is the current behaviour). If the kernel is configured with large page sizes for arm64, the user can decide to change the pageblock_order or leave the default. It is an opt-in feature for arm64. Thanks Juan