From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.188 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793303923; b=o+PwHnWA0d+5Q8OQBmiJzpsk93JmS16QZ3GKJjXNiygqOMfXFxSOj086JbNIDFj3NzHN S2SQ1LuvkzWZl72a76XPyyLjVNZABSJFKai9IXTD5DDsaphKOUvfbKzEU1SLUb+U1Zrdq 2L9rHtH7ghaSBSI4Wi6N3h+XbyQG8FsC1jyqIBQ0iXrkMg1CIMICI+btrI8Z4yHYqWvZD Ex8iw/+xfMo1DohUONi1lRW2t67wDAyh+rCzsAJAde3k8t/QyOI5hEcEMJI5YMVMdVw8A ltwffzQFiTE6QULu3G8fWHpK2igibeHQ1rYhQj79zBHl3qehOe3S/NkmwY0csxEHXxQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793303923; 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=pVeEdJtlXA25iorxAj4BG6N6zIAVHrWYsjlt6JZGNBA=; b=ugUn53+zZOi2Q8ThRQbZjQjd8yMxtIG/o88kZjdesOMTmI5RvR2QANL3HJ13CGXNCosQ CqT9rLvT/nsWFPQy2OcY4p/adKfwBMVkfP8wWK17R7vAW9gE6Htw4Co5BOZ0RlQ0o7TWb WAyLClNyMDD6vLZVF20nu1G8beKeJlU0P4lTsLqVim+aatAl5JoYGeOdBjUTL79Q28CfU HR4dWZmlX7qeQP13TOWDNJSb926W19mPhtMaR1xAH3MszmYNA3OXIn1R2I6R5ePy81Ki3 3DldE7DSwzOh+4EtLjhZVrNFiOUMuYhmaiLZlncl+KrTDEWl797Sgrv4odILKh2lIFQ== 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=hEe2oV5n; arc=none smtp.remote-ip=95.215.58.188 Received: from mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (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 2C45F606A329 for ; Thu, 29 Oct 2026 19:58:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 2C45F606A329 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=hEe2oV5n X-Envelope-To: cgroups@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=Rv8ify/EDz+JQqoM8pTjIvCmOvRL5bSqPDPKODDV4kg=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793303919; v=1; x=1793908719; b=hEe2oV5nqrcMnFsNW5746z+Cp1JNiXRXKgKx3cYeiTMjXe5ZYZz33Zj8ppVLV2wud5vTYhAV Z0BS+/26uakHvBxM64v4rrsYb55aRJAF/YsiaSbK9kYstKHyX+2LaaauYoVT45C0Jtg800/LAZ4 Ao5XbzB3bw2hb8IgIjoCKnNI= X-Envelope-To: cgroups@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 400292d4dbe12dae; Thu, 29 Oct 2026 19:58:39 +0000 X-Mizu-Trace-ID: 400292d4dbe12dae X-Migadu-Flow: FLOW_OUT Date: Thu, 29 Oct 2026 12:58:34 -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 v3 1/4] memcg: Remove unnecessary READ_ONCE() under memcg_stock.lock. Message-ID: References: <20261029194452.3189365-1-kuniyu@google.com> <20261029194452.3189365-2-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: <20261029194452.3189365-2-kuniyu@google.com> On Thu, Oct 29, 2026 at 07:44:12PM +0000, Kuniyuki Iwashima wrote: > this_cpu_ptr(&memcg_stock)->{cached[],nr_pages[]} are always > modified under local_lock(&memcg_stock.lock). > > 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(): > > Before: > > cached = READ_ONCE(stock->cached[i]); > 4c 8b 80 88 d7 bd 84 movq -0x7b422878(%rax), %r8 > if (memcg == READ_ONCE(stock->cached[i])) { > 48 3b 98 88 d7 bd 84 cmpq -0x7b422878(%rax), %rbx > 0f 84 86 01 00 00 je 0xffffffff817d01e0 > > After: > > cached = stock->cached[i]; > 4c 8b 88 88 d7 bd 84 movq -0x7b422878(%rax), %r9 > if (memcg == stock->cached[i]) { > 4c 39 cb cmpq %r9, %rbx > 0f 84 7a 01 00 00 je 0xffffffff817d01d0 > > Signed-off-by: Kuniyuki Iwashima Acked-by: Shakeel Butt