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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: <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: EA0A440015 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 4u6t4zdttxpdxdwsyqajf8mpuskndq6p X-HE-Tag: 1684459477-288175 X-HE-Meta: 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 g+ThUc2v qvSpJAt8HDrmXAJ2kiinBw+XMNzZK5UJLzSyVRcQ6YZ2Erko0PL9kJB4wfqxTwOnCs7BvG596piOVP1tGzmHyVWVZTp0SBNu/GJZc 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 01:51:08PM -0700, Song Liu wrote: > To allocate memory for text, we will allocate 2MiB, make it ROX, and then > use it for many small allocations. IIUC, buddy allocator will use unallocated > parts of this page for metadata. I guess this may be a problem, as the > whole page is ROX now, and we have to use text_poke to write to it. The standard kernel buddy allocator does _not_ store anything in the page itself - because the page might be a highmem page. That's also why I went with the bitmap for my slab allocator; standard kernel slab allocator stores a freelist ptr in free objects.