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From: Shakeel Butt To: Yosry Ahmed Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/7] memcg: reduce memory size of mem_cgroup_events_index Message-ID: References: <20240427003733.3898961-1-shakeel.butt@linux.dev> <20240427003733.3898961-2-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 5774D18000C X-Stat-Signature: sbrw9cyho5kqfrgjnhwb59cjespe8re4 X-HE-Tag: 1714180520-290464 X-HE-Meta: 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 bKyTOQoy L6QYNlQrvZCYE1vpzGF1y/jEhACW7m1chXhIPMPmRWL3mRXGjoMNfypsI1mArayWWnNFxCCw309hkz5LTo14/bN+6WcHb2G4W1/LoE7eq0unmAqtnfdhQBJc16A== 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: List-Subscribe: List-Unsubscribe: On Fri, Apr 26, 2024 at 05:42:48PM -0700, Yosry Ahmed wrote: > On Fri, Apr 26, 2024 at 5:37 PM Shakeel Butt wrote: > > > > mem_cgroup_events_index is a translation table to get the right index of > > the memcg relevant entry for the general vm_event_item. At the moment, > > it is defined as integer array. However on a typical system the max > > entry of vm_event_item (NR_VM_EVENT_ITEMS) is 113, so we don't need to > > use int as storage type of the array. For now just use int8_t as type > > and add a BUILD_BUG_ON() and will switch to short once NR_VM_EVENT_ITEMS > > touches 127. > > Any reason not to use uint8_t (or simply u8) and U8_MAX (instead of > the hardcoded 127)? > Just to keep the error check simple i.e. (index < 0). If we hit 127 then we can switch to uint8_t and S8_MAX as error. Though 127 should be replaced by S8_MAX. Somehow I was grep'ing for INT8*MAX variants. Anyways if there is more support for uint8_t, I will change otherwise I will keep as is.