From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta0.migadu.com (out-187.mta0.migadu.com [91.218.175.187]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 051021DE4F6 for ; Tue, 26 Nov 2024 19:29:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732649368; cv=none; b=V7FKvPAmMS0VpCOR3gts0lsoV2h9gBNKeBybtDGj0SVUYR6HZASlR9o7aggpaMMimPihFo/zaAZowCAtbo8f+fU2Rt5UWz3SjoY3D2TXadwP7Uck2U4QPuwcg+qFO5QQG4rl6TzkAWcsdsZ2+rhrlzl3vEVMHLODnFnJ3xNAUR8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732649368; c=relaxed/simple; bh=oA/qdV6gyIyfl9AXAgDB9I+NgI2XOp2Rl5kd2AhTO+s=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=slaKOrXvlFd/Vkov5PQX5CVUtSKdT/QeS6u7xscUNaGVwDofHJtJvq5U4go+Hoa/L7XeAaBH858pox9DlaXwNw4V+P+JcquE2uKeJJ2kKt6FDH97HHFcxOZYT5N1umjHxapw5YFsPcTGb7KCUlc+GznKd0N6DjCw2wJjHfSKcI4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Oq/8LgXz; arc=none smtp.client-ip=91.218.175.187 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) header.d=linux.dev header.i=@linux.dev header.b="Oq/8LgXz" Date: Tue, 26 Nov 2024 19:29:14 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1732649360; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zEUa6tKt5tK0Kb57WdB49xzZN3WpeLv/SaNRuQje//8=; b=Oq/8LgXzoMjfOZGiAo69b54cDx2xC/O33Xxq1O86CuJtUgIufZdOmePR93HnrRUHRdmbPW O1JsUBDgqxRMNuWYBpulfNrAyOJERwusIbg02U7UrDx0ktcQprdT5e4uphkNjGxdX1B3cy vtyMCjWyLxYfq0FYXNfpaWuxHp+8IOk= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Muchun Song , Vlastimil Babka , Axel Rasmussen , Steven Rostedt , Suren Baghdasaryan , Matthew Wilcox , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH v2] mm: mmap_lock: optimize mmap_lock tracepoints Message-ID: References: <20241125171617.113892-1-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241125171617.113892-1-shakeel.butt@linux.dev> X-Migadu-Flow: FLOW_OUT On Mon, Nov 25, 2024 at 09:16:17AM -0800, Shakeel Butt wrote: > We are starting to deploy mmap_lock tracepoint monitoring across our > fleet and the early results showed that these tracepoints are consuming > significant amount of CPUs in kernfs_path_from_node when enabled. > > It seems like the kernel is trying to resolve the cgroup path in the > fast path of the locking code path when the tracepoints are enabled. In > addition for some application their metrics are regressing when > monitoring is enabled. > > The cgroup path resolution can be slow and should not be done in the > fast path. Most userspace tools, like bpftrace, provides functionality > to get the cgroup path from cgroup id, so let's just trace the cgroup > id and the users can use better tools to get the path in the slow path. > > Signed-off-by: Shakeel Butt Acked-by: Roman Gushchin Thanks!