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Wed, 26 Feb 2025 19:04:55 -0800 (PST) Received: from [10.68.122.90] ([63.216.146.179]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-aee7de1a4absm310575a12.26.2025.02.26.19.04.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Feb 2025 19:04:55 -0800 (PST) Message-ID: Date: Thu, 27 Feb 2025 11:04:51 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: CONFIG_PT_RECLAIM To: Johannes Weiner Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250226183013.GB1042@cmpxchg.org> From: Qi Zheng In-Reply-To: <20250226183013.GB1042@cmpxchg.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: o53ugebp6y1cdtotrqiw54bhcu17psuk X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: F184320006 X-Rspam-User: X-HE-Tag: 1740625496-53637 X-HE-Meta: U2FsdGVkX18UH549qbL37Ll4LG1MUV+K34FnntoC9fJVfMZY94pemnuawMA/i/PnZLWFUDCidHoWZZzl09ddd7aQxUQV7rpBeyDQBDQgrBRoGnFKQu9FjxHGPYrMWNpRpVNReam1hCEMDADazP1bhL7tYDb+T2M57TbMD3s86uh/8dfRMXIfXmnoBiBoxxhQLU4JRYeuedCQj7CGVSbkSu9jp/k0zVOKlmndzgSF+rMaslOMFx8SHnQtkDsLb7xT2x0LEhSbft/Dwm+TNqA0FEWWpPyG0fhYFSjo1gCIuKPbMlU8wYyuyNM3A+5T6PP35BJ8zigfv0YxJq0fYN2O4gX7ZOyjI87EmWxzvnFh+HKqoY6yJyQt8S4+1W2VVozZU1fstE/EdLjZ9062QcrXOvy1Y8Om9ytaBukA798EMeujZMPJYzCuA7eymewg9SJviYWIQrnensqz89TlRUruimsoVEmcnWMGdd7tO7muumeqexDyTuS4B93LQWEmtZmOOkQnJUVVlZ+ZU7EXB/0HaNyGDi6MuymVBNjvHKfZ0v0VZuUdGooc+fQPBf4TNNMB27hHfgI8VfdZycarT8b+k9RZDjRmD2BfJjtNz6zz++6TYl8yVfekZKHCh/h+SZvnEwgUjrwTPx6wZ4xk+QGDW+hazP2dG9olB9dHt51e9d88osHkPelaS9rcJ/nA+TjV86BToR/aSA2c1y278l/krtMc3gK24LmMFB52qMiwASg7R6CMkX+4vpaTXS7dBh7NlesuwaWhch2syscAjZb5i8wJ9n202ip1h5NDVpqHuVDK6cXUjcmCcPEbppbTLG+RG9kZkadKycwERNqq7cxbCSXBBxrfzUFfb8Nq7vApFCZvD0VfIYl4kOz9vJ6riSctBVU0wuAyAa+TrGxkrBbJ+QbRfpcJ0na+X/ARKLRRFIYksHM4R6gl1wEh2KzUbhMcz7G5ch6cWvjBYq8mv12 xtYGHqZC 6enNdRxwNWsMtOLZeFdHWu/t/3WVa56dEpKCQursfnXw22A+kTh0odCuTyZnFEmmE9o2Sal7307n62AYhee76A6knuENlg29BDbCWyRzOpI9bXYffRj4imfQ8HyhaikX6XB8ky2qt6F73ukiRVbaRPKQNsLOfPn0KrylH4xxG/whM2DEwMo6kV8B9XVrGp2IZ69TNr7kFZHhPH2FD1/iTPhcdElvxdlRx9fbh2zP8LM6bogwsrWxd6xSq7ss9KvqzXJna3kjcC00VUu4PcIyl3/pcC/sXnZm8FV9uGcQi9xw0TOWordW6awrmadGvIzPNbnC6HcD+1eGBrcbgkBQR9MiM89hIdUaUZFWn1FbCIE2r9BT2WRDvEPv0qyHqWAsbSotl8WMlAEMAI4X055QHQ++tow== X-Bogosity: Ham, tests=bogofilter, spamicity=0.086195, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Johannes, On 2/27/25 2:30 AM, Johannes Weiner wrote: > Does PT_RECLAIM need to be configurable by the user? The PT_RECLAIM will select MMU_GATHER_RCU_TABLE_FREE, but not all archs support MMU_GATHER_RCU_TABLE_FREE, and even before Rik's a37259732a7dc ("x86/mm: Make MMU_GATHER_RCU_TABLE_FREE unconditional"), x86 only supports MMU_GATHER_RCU_TABLE_FREE in the case of PARAVIRT. Therefore, PT_RECLAIM also implies the meaning of enabling MMU_GATHER_RCU_TABLE_FREE, so I made it user-configurable. And I just thought that as a new feature, it would be better to give users the ability to turn it on and off. > > Why not always try to free the page tables if the arch supports it? If so, maybe changing select MMU_GATHER_RCU_TABLE_FREE to depends on MMU_GATHER_RCU_TABLE_FREE would be better? > > diff --git a/mm/Kconfig b/mm/Kconfig > index 2761098dbc1a..99383c93db33 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -1309,16 +1309,9 @@ config ARCH_SUPPORTS_PT_RECLAIM > def_bool n > > config PT_RECLAIM > - bool "reclaim empty user page table pages" > - default y > + def_bool y > depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP > select MMU_GATHER_RCU_TABLE_FREE > - help > - Try to reclaim empty user page table pages in paths other than munmap > - and exit_mmap path. > - > - Note: now only empty user PTE page table pages will be reclaimed. > - Maybe keep the help information? Thanks, Qi > > source "mm/damon/Kconfig" >