From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 077386B0292 for ; Fri, 11 Aug 2017 06:50:25 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id d5so33763024pfg.3 for ; Fri, 11 Aug 2017 03:50:24 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [65.50.211.133]) by mx.google.com with ESMTPS id t20si374619plj.397.2017.08.11.03.50.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 11 Aug 2017 03:50:23 -0700 (PDT) Date: Fri, 11 Aug 2017 12:50:15 +0200 From: Peter Zijlstra Subject: Re: [PATCH v6 3/7] Revert "mm: numa: defer TLB flush for THP migration as long as possible" Message-ID: <20170811105015.4njdpy3il76g5uuk@hirez.programming.kicks-ass.net> References: <20170802000818.4760-1-namit@vmware.com> <20170802000818.4760-4-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170802000818.4760-4-namit@vmware.com> Sender: owner-linux-mm@kvack.org List-ID: To: Nadav Amit Cc: linux-mm@kvack.org, nadav.amit@gmail.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Minchan Kim , Sergey Senozhatsky , Andy Lutomirski On Tue, Aug 01, 2017 at 05:08:14PM -0700, Nadav Amit wrote: > While deferring TLB flushes is a good practice, the reverted patch > caused pending TLB flushes to be checked while the page-table lock is > not taken. As a result, in architectures with weak memory model (PPC), > Linux may miss a memory-barrier, miss the fact TLB flushes are pending, > and cause (in theory) a memory corruption. > > Since the alternative of using smp_mb__after_unlock_lock() was > considered a bit open-coded, and the performance impact is expected to > be small, the previous patch is reverted. FWIW this Changelog sucks arse; you completely fail to explain the broken ordering. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org