From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f197.google.com (mail-io0-f197.google.com [209.85.223.197]) by kanga.kvack.org (Postfix) with ESMTP id 53F836B4E3E for ; Wed, 29 Aug 2018 19:15:50 -0400 (EDT) Received: by mail-io0-f197.google.com with SMTP id l6-v6so5979864iog.4 for ; Wed, 29 Aug 2018 16:15:50 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v128-v6sor47196ith.25.2018.08.29.16.15.49 for (Google Transport Security); Wed, 29 Aug 2018 16:15:49 -0700 (PDT) MIME-Version: 1.0 References: <20180828112034.30875-1-npiggin@gmail.com> <20180828112034.30875-3-npiggin@gmail.com> <20180830091213.78b64354@roar.ozlabs.ibm.com> In-Reply-To: <20180830091213.78b64354@roar.ozlabs.ibm.com> From: Linus Torvalds Date: Wed, 29 Aug 2018 16:15:37 -0700 Message-ID: Subject: Re: [PATCH 2/3] mm/cow: optimise pte dirty/accessed bits handling in fork Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Nick Piggin Cc: linux-mm , linux-arch , Linux Kernel Mailing List , ppc-dev , Andrew Morton On Wed, Aug 29, 2018 at 4:12 PM Nicholas Piggin wrote: > > Dirty micro fault seems to be the big one for my Skylake, takes 300 > nanoseconds per access. Accessed takes about 100. (I think, have to > go over my benchmark a bit more carefully and re-test). Yeah, but they only happen for shared areas after fork, which sounds like it shouldn't be a big deal in most cases. And I'm not entirely objecting to your patch per se, I just would want to keep the accessed bit changes separate from the dirty bit ones. *If* somebody has bisectable issues with it (performance or not), it will then be clearer what the exact issue is. Linus