From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 BD7F224B4A for ; Fri, 31 May 2024 22:10:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717193406; cv=none; b=pjoCSPZVDNCP3J85ZxcDo5G6xhNq/n9H9BV+HXeneqDQxgIUijDZjzCCrN5cCt48+f7qEPPIEUQ0zHzNFrBSfZjjgCcr7Mre/f7+3DXQK2OVzMSiN+nYHVz4xb8PAX+d2sRzg+1tkRSo+Df3X8TQdioGgH5RQ+yqNoLMMwkxiKA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717193406; c=relaxed/simple; bh=neMthn+my1WAJWqEpUsCTbkhD0SCbK/9kqeYHZgSIWQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cXneCoUxFxVrYy23A8PpnDyXUoim80sOgL7v+c5+cI19wwEvftcM9ZTOIqfncMBoMao88K9WybOK0bl5PzC5rh/708igP8ixQzu3SacEKuix4l0bhg+v881p/QkKIzSM3Y+tA5R/YRJ/McIKB23FQTwXyA12BcuvlvnbUPmxU5Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=YOAb47UN; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="YOAb47UN" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=MkS6taIPYxq4oexTWP4Nym8gBT1BhbKY0UZv23zB09c=; b=YOAb47UNG4kr8fjujJxJLocaah gAD8nRmrJmfY16d/vHGhG/ULklZSzFjKDEQj5Jsvt6jNIBVa2xYYwK0g9e5tZ9eyi1BEkZQPMEUXu LYjXw/PsVwoiWXHEwmTlg6s8+eWAFGraVhRyXIB2rHlue3eyQU7efWdgwvMux7vX9jSJfw95vIuW0 CDxs+adDaRuBRPjULIb1qHKNhi5q4CxrlWJAisHnMltsxKLWucQZ0ynCzb0VVxreZfGYyVDv8jxs8 7Dl1Q8BGXCO/5sDZ/TqL9Q2dBpe+kPcp9lMyAsWeT25aYFO5bjLIyDsUTu3mN3M0FUC8EZqR/RFFA AyLcaXPQ==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sDARW-0000000C4jN-2aQL; Fri, 31 May 2024 22:09:46 +0000 Date: Fri, 31 May 2024 23:09:46 +0100 From: Matthew Wilcox To: Dave Hansen Cc: Byungchul Park , Byungchul Park , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, akpm@linux-foundation.org, ying.huang@intel.com, vernhao@tencent.com, mgorman@techsingularity.net, hughd@google.com, david@redhat.com, peterz@infradead.org, luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, rjgolo@gmail.com Subject: Re: [PATCH v11 09/12] mm: implement LUF(Lazy Unmap Flush) defering tlb flush when folios get unmapped Message-ID: References: <20240531092001.30428-1-byungchul@sk.com> <20240531092001.30428-10-byungchul@sk.com> 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: On Fri, May 31, 2024 at 02:46:23PM -0700, Dave Hansen wrote: > On 5/31/24 11:04, Byungchul Park wrote: > ... > > I don't believe you do not agree with the concept itself. Thing is > > the current version is not good enough. I will do my best by doing > > what I can do. > > More performance is good. I agree with that. > > But it has to be weighed against the risk and the complexity. The more > I look at this approach, the more I think this is not a good trade off. > There's a lot of risk and a lot of complexity and we haven't seen the > full complexity picture. The gaps are being fixed by adding complexity > in new subsystems (the VFS in this case). > > There are going to be winners and losers, and this version for example > makes file writes lose performance. > > Just to be crystal clear: I disagree with the concept of leaving stale > TLB entries in place in an attempt to gain performance. FWIW, I agree with Dave. This feels insanely dangerous and I don't think you're paranoid enough about things that can go wrong.