From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.158 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793234915; b=cTrAVHLTbooeZtECLPWwvwoNvC8wfNDHP/z1OJt9BHDac8XcdxS6v25j2Dfi3Wh07V7S etSTr/qN7keKiBBsWKF06NrN+XuhSmaR8eiPJ2b/91NNPIsxB04YcSfhPC2Jl5+yo/j83 hvsmFawSYmNfJQ2CLB3MZZ6co/oERRfUX//eBIoyt4KtrmCOWUCqBgMq1EsfygKqqv80E KMoD6kuad130DxhCOF/Am93kwMzWxtmE9clONueI/JiR16zj+GV8osm5Fjt/kSiGOZ09q JP7sYFtQhdhRBHiw6ezEkb5vaYJgNHzQF/alXWOFjGgxCNqM+M6cF/LLXsaTgs7uCHw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793234915; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=RBKUF6AXFgaSWUb7Kj83+bMmMJKcRCg8xBUXyTLPZYg=; b=VlnPTLLOKCxDM+ilOCmntWq2SqrkZy3UuFD69BtiRZ7MY5SNPT3XeI6VryGIJA4kTWGc Cy619kxOgZygB5KhvbI2duMa5Q7TDpK2vnLmNfm+koRWQKhD0ZdjAIVODfpVoRXxlOrkQ QWN5JrLc/9hI+C4QA91GGkc5E9Nu8t8NZxjcRnn7imHC4KC9dsnirRDrfIymnoYAKO5vL /KCYw48sX5CIRPX2QLWe38UpkVqyyaKVkw4ltVuepAK52MQ/xkLif7FlxqOnycVKq00eZ 4K16TAgg4iODQZpOTmaG1tqtMA7ER7OVkIElToXI2f2Auxaj50VtOWItM/vIEiH3s8A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=r2ZgFIxE; arc=none smtp.remote-ip=91.218.175.158 Received: from mta0.migadu.com (out-158.mta0.migadu.com [91.218.175.158]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4D3E4606A31A for ; Thu, 29 Oct 2026 00:48:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 4D3E4606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=r2ZgFIxE X-Envelope-To: cgroups@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=YzQ2Pc3WwUtKoWDSH3+5WqZrrR/yZR7jr8YByoE6Vi8=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793234912; v=1; x=1793839712; b=r2ZgFIxEQRb9AtUouSFKV6VSKOIXUP2YOx2IHFPt/8gnhloT9z5A1CloHOOkRVYqgWUftXaN D/WK8Liiw/xy6PZddQDq0PeZqi+mx7Va9e9xD73gwJp0cB31fVpk1zehpE/3/yW+3sJIpY72n2B K1S22oh0jnVfwnjpLsTMZEfs= X-Envelope-To: cgroups@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 469ed800a9d69200; Thu, 29 Oct 2026 00:48:32 +0000 X-Mizu-Trace-ID: 469ed800a9d69200 X-Migadu-Flow: FLOW_OUT Date: Wed, 28 Oct 2026 17:48:26 -0700 From: Shakeel Butt To: Kuniyuki Iwashima Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Kuniyuki Iwashima , linux-mm@kvack.org, cgroups@vger.kernel.org Subject: Re: [PATCH v2 1/6] memcg: Remove unnecessary READ_ONCE() under memcg_stock.lock. Message-ID: References: <20261028185034.3607746-1-kuniyu@google.com> <20261028185034.3607746-2-kuniyu@google.com> X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261028185034.3607746-2-kuniyu@google.com> On Wed, Oct 28, 2026 at 06:50:13PM +0000, Kuniyuki Iwashima wrote: > this_cpu_ptr(&memcg_stock) is always modified under > local_lock(&memcg_stock.lock). You need to be more precise here. Mainly the cached[] and nr_pages[] are only modified under the local lock. There is flags field which is being modified without it. > > Unlike is_memcg_drain_needed() under RCU, consume_stock(), > drain_stock(), and refill_stock() do not need READ_ONCE(). > > Especially, in refill_stock(), READ_ONCE() is used twice for > stock->cached[i], which forces the compiler to emit two volatile > loads from stock->cached[i]. > > Let's remove the unnecessary READ_ONCE() and eliminate the > redundant loads in refill_stock(): What are we gaining with that? Is this measurable? With READ_ONCE() at least we are very explicit that this field can read and modified concurrently by different CPUs i.e. better readability.