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X-IronPort-AV: E=McAfee;i="6600,9927,10993"; a="6858582" X-IronPort-AV: E=Sophos;i="6.06,180,1705392000"; d="scan'208";a="6858582" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Feb 2024 10:23:26 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.06,180,1705392000"; d="scan'208";a="10584169" Received: from gtkramer-mobl1.amr.corp.intel.com (HELO [10.209.82.163]) ([10.209.82.163]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Feb 2024 10:23:23 -0800 Message-ID: <05a12c0b-e3e3-4549-b02e-442e4b48a86d@intel.com> Date: Fri, 23 Feb 2024 10:23:21 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 16/20] famfs: Add fault counters Content-Language: en-US To: John Groves , John Groves , Jonathan Corbet , Dan Williams , Vishal Verma , Dave Jiang , Alexander Viro , Christian Brauner , Jan Kara , Matthew Wilcox , linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev Cc: john@jagalactic.com, Dave Chinner , Christoph Hellwig , dave.hansen@linux.intel.com, gregory.price@memverge.com References: <43245b463f00506016b8c39c0252faf62bd73e35.1708709155.git.john@groves.net> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/23/24 09:42, John Groves wrote: > One of the key requirements for famfs is that it service vma faults > efficiently. Our metadata helps - the search order is n for n extents, > and n is usually 1. But we can still observe gnarly lock contention > in mm if PTE faults are happening. This commit introduces fault counters > that can be enabled and read via /sys/fs/famfs/... > > These counters have proved useful in troubleshooting situations where > PTE faults were happening instead of PMD. No performance impact when > disabled. This seems kinda wonky. Why does _this_ specific filesystem need its own fault counters. Seems like something we'd want to do much more generically, if it is needed at all. Was the issue here just that vm_ops->fault() was getting called instead of ->huge_fault()? Or something more subtle?