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Wed, 22 May 2024 05:45:19 -0700 (PDT) Received: from ziepe.ca ([128.77.69.89]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6a15f17b4cfsm131592176d6.26.2024.05.22.05.45.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 May 2024 05:45:19 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1s9lLJ-00C8xv-OI; Wed, 22 May 2024 09:45:17 -0300 Date: Wed, 22 May 2024 09:45:17 -0300 From: Jason Gunthorpe To: Uros Bizjak Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Kevin Tian , Joerg Roedel , Will Deacon , Robin Murphy Subject: Re: [PATCH 3/3] iommufd: Use atomic_long_try_cmpxchg() in incr_user_locked_vm() Message-ID: <20240522124517.GB69273@ziepe.ca> References: <20240522082729.971123-1-ubizjak@gmail.com> <20240522082729.971123-3-ubizjak@gmail.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240522082729.971123-3-ubizjak@gmail.com> On Wed, May 22, 2024 at 10:26:49AM +0200, Uros Bizjak wrote: > Use atomic_long_try_cmpxchg() instead of > atomic_long_cmpxchg (*ptr, old, new) != old in incr_user_locked_vm(). > cmpxchg returns success in ZF flag, so this change saves a compare > after cmpxchg (and related move instruction in front of cmpxchg). > > Also, atomic_long_try_cmpxchg() implicitly assigns old *ptr > value to "old" when cmpxchg fails. There is no need to re-read > the value in the loop. > > Signed-off-by: Uros Bizjak > Cc: Jason Gunthorpe > Cc: Kevin Tian > Cc: Joerg Roedel > Cc: Will Deacon > Cc: Robin Murphy > --- > drivers/iommu/iommufd/pages.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) Reviewed-by: Jason Gunthorpe This patch may as well go through Joerg's tree with the whole series Thanks, Jason