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From: Kent Overstreet To: Song Liu Cc: Mike Rapoport , linux-mm@kvack.org, Andrew Morton , Dave Hansen , Peter Zijlstra , Rick Edgecombe , Thomas Gleixner , Vlastimil Babka , linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [RFC PATCH 1/5] mm: intorduce __GFP_UNMAPPED and unmapped_alloc() Message-ID: References: <20230308094106.227365-1-rppt@kernel.org> <20230308094106.227365-2-rppt@kernel.org> <20230518152354.GD4967@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 0D043180012 X-Rspam-User: X-Stat-Signature: m8aojftp8jtkcc95s5hq8iitxuce1eeu X-Rspamd-Server: rspam03 X-HE-Tag: 1684437379-374211 X-HE-Meta: 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 abt+yHc2 D//xqgP/HBU3zC3mRsK0Xg7fogN//9BdcuLJDszVmYebMu2+kEqloUXbXINO8PunGHKI2W4qDUipVdDgwZ1S120poO09gheoTE8jdRuQUyZsRgtNMft1Fm4i/Fg== 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 Thu, May 18, 2023 at 12:03:03PM -0700, Song Liu wrote: > > Second, bitmap based solution cannot handle > 2MiB allocation cleanly, > > while tree based solution can. For example, if a big driver uses 3MiB, the > > tree based allocator can allocate 4MiB for it, and use the rest 1MiB for > > smaller allocations. 2 MB is just a good default size for the initial unmapped allocations if the main consideration is avoiding mapping fragmentation. The approach can work with larger allocations if required.