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bh=l7SbKU9F9qydFA63ScSFIvkpFCyV2VwENOTEfPuxH1U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k3pwUNWGjWJ7oF2B7SdpVX0kEW5mVBH3e5ZgCwzY0DqHClrl2OH9v2TiXTY3xew4G Udbqy3DPZoez1xv46q48OXrvV4GYbLZB59fkzE0xIJF49J2SRFaNFs7QgQsnB/LuUZ 39ueqpB/dUCOAQVazye3+lt9qzOaGVvAbSBRtYqy7moQNsUKItnEuG2+Mf3JmR9g8S PxXg88SKzdWxMqmnUlseR1lsRgHa4wM8gwjiixaqpd/um96DT0iLNVGI8LO5Eo5oGa 0eOlBwtdNrOOUFU8BxJO2zChUy7Tpfo8rrQgQRweM9dT8BZR4Rg7LveJRlXajfXRbL S/NQSN4sYBN8w== From: SeongJae Park To: Matthew Wilcox Cc: SeongJae Park , akpm@linux-foundation.org, vbabka@suse.cz, paulmck@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code Date: Sat, 15 Apr 2023 16:27:39 +0000 Message-Id: <20230415162739.5898-1-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: e8yqm1k3zz5tps5u6equwnxagmhadstk X-Rspam-User: X-Rspamd-Queue-Id: D724B180009 X-Rspamd-Server: rspam06 X-HE-Tag: 1681576063-604135 X-HE-Meta: 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 ND9Ff/YT Y4R/yj6WhffY1cuksMRBbcWU8YYnmiC7dFJijCgt0NmA/xEau1gP74BWc6HTdM23nl+KrXBq1C5y21/vaUz0iWuJy3qaJQrMg5kIrNlEp5sLsC0avxclGpyXJAkBO4YByaQ5mihnJspcjCz6PemubBl7wy9Ko5bJTsoxCcR/axZfMLpIbfboYCff+8dyd7Hd9D95Eur1MrIPRkg9Q681/4ur1cPdeeHfLL4eZYAU6Oz5pBRDjQ3eoQU6t2VjA9YVaTHGtc5EpeiMfpdWxr8xWg1qHFOFaTVYVC1xxn7RSCa+djLHjaGsIR+tTb06KiEA3C+ACrfmfdo4szHJkytFS9kPLiePbor0QUrQqWImF5TRndLx+mXXDQMWkcXq7o1jTn88bUD+dKMlRQ9tZW+Z2Wj/LFw== 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 Sat, 15 Apr 2023 04:49:44 +0100 Matthew Wilcox wrote: > On Sat, Apr 15, 2023 at 03:31:59AM +0000, SeongJae Park wrote: > > The SLAB_TYPESAFE_BY_RCU example code snippet is having not tiny RCU > > read-side critical section. 'Documentation/RCU/rculist_nulls.rst' has > > similar example code snippet, and commit da82af04352b ("doc: Update and > > wordsmith rculist_nulls.rst") has broken it. Apply the change to > > SLAB_TYPESAFE_BY_RCU example code snippet, too. > > so the page cache (eg find_get_entry()) does not follow this "split > the RCU critical section" pattern. Should it? What's the benefit? The benefit would be shorter RCU grace period that allows lower memory footprint, iiuc. Whether it should split the section or not would depend on the lookup speed and number of retries, I think. If the total lookup takes a time that long enough to make the grace period too long and therefore the amount of RCU-protected objects that cannot freed due to the grace priod is huge, I think it would better to follow the pattern. Thanks, SJ