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[2003:cb:c708:1d00:99ec:9656:7475:678d]) by smtp.gmail.com with ESMTPSA id m6-20020a5d4a06000000b003330aede2aesm2717126wrq.112.2023.11.28.08.58.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Nov 2023 08:58:56 -0800 (PST) Message-ID: <2e2d3f51-34e3-4982-b982-ab7b555cba21@redhat.com> Date: Tue, 28 Nov 2023 17:58:55 +0100 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 06/27] mm: page_alloc: Allow an arch to hook early into free_pages_prepare() Content-Language: en-US To: Alexandru Elisei Cc: catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, arnd@arndb.de, akpm@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, mhiramat@kernel.org, rppt@kernel.org, hughd@google.com, pcc@google.com, steven.price@arm.com, anshuman.khandual@arm.com, vincenzo.frascino@arm.com, eugenis@google.com, kcc@google.com, hyesoo.yu@samsung.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org References: <20231119165721.9849-1-alexandru.elisei@arm.com> <20231119165721.9849-7-alexandru.elisei@arm.com> <45466b05-d620-41e5-8a2b-05c420b8fa7b@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 27.11.23 14:03, Alexandru Elisei wrote: > Hi, > > On Fri, Nov 24, 2023 at 08:36:52PM +0100, David Hildenbrand wrote: >> On 19.11.23 17:57, Alexandru Elisei wrote: >>> Add arch_free_pages_prepare() hook that is called before that page flags >>> are cleared. This will be used by arm64 when explicit management of tag >>> storage pages is enabled. >> >> Can you elaborate a bit what exactly will be done by that code with that >> information? > > Of course. > > The MTE code that is in the kernel today uses the PG_arch_2 page flag, which it > renames to PG_mte_tagged, to track if a page has been mapped with tagging > enabled. That flag is cleared by free_pages_prepare() when it does: > > page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; > > When tag storage management is enabled, tag storage is reserved for a page if > and only if the page is mapped as tagged. When a page is freed, the code looks > at the PG_mte_tagged flag to determine if the page was mapped as tagged, and > therefore has tag storage reserved, to determine if the corresponding tag > storage should also be freed. > > I have considered using arch_free_page(), but free_pages_prepare() calls the > function after the flags are cleared. > > Does that answer your question? Yes, please add some of that to the patch description! -- Cheers, David / dhildenb