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[59.102.81.67]) by smtp.gmail.com with ESMTPSA id g5-v6sm15723018pgn.73.2018.08.29.16.57.50 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 29 Aug 2018 16:57:53 -0700 (PDT) Date: Thu, 30 Aug 2018 09:57:47 +1000 From: Nicholas Piggin To: Linus Torvalds Cc: linux-mm , linux-arch , Linux Kernel Mailing List , ppc-dev , Andrew Morton Subject: Re: [PATCH 2/3] mm/cow: optimise pte dirty/accessed bits handling in fork Message-ID: <20180830095747.491f7770@roar.ozlabs.ibm.com> In-Reply-To: References: <20180828112034.30875-1-npiggin@gmail.com> <20180828112034.30875-3-npiggin@gmail.com> <20180830091213.78b64354@roar.ozlabs.ibm.com> X-Mailer: Claws Mail 3.17.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 29 Aug 2018 16:15:37 -0700 Linus Torvalds wrote: > 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. You might be right there. > > 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. Yeah that makes a lot of sense. I'll do a bit more testing and send Andrew a respin at least with those split (and a good comment for the dirty bit vs unmap handling that you pointed out). Thanks, Nick