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Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song Subject: Re: [PATCH v7 08/14] KVM: Rename mmu_notifier_* Message-ID: References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com> <20220706082016.2603916-9-chao.p.peng@linux.intel.com> <20230524203336.GC3447678@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230524203336.GC3447678@hirez.programming.kicks-ass.net> X-TM-AS-GCONF: 00 X-Proofpoint-GUID: JMCMkBzE0_vErxya7Uw2ZgGvqaMed5tP X-Proofpoint-ORIG-GUID: bS2bLfFp6dr_ipd_3qmflAOTtlaGVqG_ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.176.26 definitions=2023-05-24_17,2023-05-24_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 phishscore=0 clxscore=1011 spamscore=0 adultscore=0 suspectscore=0 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=901 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305250027 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 18A88140005 X-Stat-Signature: htqa97z5jui7uqgmxraoywp1qdcbkzje X-Rspam-User: X-HE-Tag: 1684986787-376717 X-HE-Meta: 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 AZKi6M9G L7JAwJRFV/tvzrfPHTZ/AwVOixydKPAzh3i10fNP13HzG7wKfOzah9Dqr+khi+PewJnm9wSop/WBN8h74TyfkO2/PtqzFYkMAPtu8w5M+pOx6W2Wy9YadFqDWJjmThxwFbCV3fUygqMuDRMUxse6/3GvlKrycbAlyv5wkLxGJOJnDr6w= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023-05-24 22:33:36, Peter Zijlstra wrote: > On Wed, May 24, 2023 at 01:16:03PM -0700, Sean Christopherson wrote: > > > Atomics aren't memory barriers on all architectures, e.g. see the various > > definitions of smp_mb__after_atomic(). > > > > Even if atomic operations did provide barriers, using an atomic would be overkill > > and a net negative. On strongly ordered architectures like x86, memory barriers are > > just compiler barriers, whereas atomics may be more expensive. > > Not quite, smp_{r,w}mb() and smp_mb__{before,after}_atomic() are > compiler barriers on the TSO archs, but smp_mb() very much isn't. TSO > still allows stores to be delayed vs later loads (iow it doesn't pretend > to hide the store buffer). > > > Of course, the only > > accesses outside of mmu_lock are reads, so on x86 that "atomic" access is just a > > READ_ONCE() load, but that's not the case for all architectures. > > This is true on *all* archs. atomic_set() and atomic_read() are no more > and no less than WRITE_ONCE() / READ_ONCE(). > > > Anyways, the point is that atomics and memory barriers are different things that > > serve different purposes. > > This is true; esp. on the weakly ordered architectures where atomics do > not naturally imply any ordering. Thanks for the information, everyone.