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Wed, 22 Oct 2025 03:52:34 -0700 (PDT) MIME-Version: 1.0 References: <20251013092038.6963-1-ying.huang@linux.alibaba.com> <20251013092038.6963-3-ying.huang@linux.alibaba.com> <87a51jfl44.fsf@DESKTOP-5N7EMDA> <871pmv9unr.fsf@DESKTOP-5N7EMDA> <875xc78es0.fsf@DESKTOP-5N7EMDA> <87a51j6zg7.fsf@DESKTOP-5N7EMDA> <87ms5j4444.fsf@DESKTOP-5N7EMDA> In-Reply-To: <87ms5j4444.fsf@DESKTOP-5N7EMDA> From: Barry Song <21cnbao@gmail.com> Date: Wed, 22 Oct 2025 23:52:23 +1300 X-Gm-Features: AS18NWAP0fbsGHxZLrVjv_J-9bnvKPZdV1GwoS51_2cxWur2X2S3xT3hLu6HdG0 Message-ID: Subject: Re: [PATCH -v2 2/2] arm64, tlbflush: don't TLBI broadcast if page reused in write fault To: "Huang, Ying" Cc: Catalin Marinas , Will Deacon , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Vlastimil Babka , Zi Yan , Baolin Wang , Ryan Roberts , Yang Shi , "Christoph Lameter (Ampere)" , Dev Jain , Anshuman Khandual , Yicong Yang , Kefeng Wang , Kevin Brodsky , Yin Fengwei , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 89F794000C X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: 43z7w9u88yziee6j5reudey6zuuengk8 X-HE-Tag: 1761130355-592312 X-HE-Meta: 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 sm1Izo5K FXNZ+qJlIO91Ykv+JFAJGbmGe5/u+idiec7IMlBn/e6Kc8LZNuK/i8RP8+n0zMVZJ8p7VOmxnOQLO/9l8Hegd/8eBDwQJywpKFejujfHbghkI5ViELWmWncdOVDFhH4utIs5Ht8EIxB2lx64ZukZCXLMZbx+IU1aNAWpIa9eQwZ4BF76DQbX6wUG+XYWOYETEfDYaqB9bkc2e+Xnp7SRGdvq2ZVR23VAyXeedTquFJl8d3mH+bk7z3BSn3KyJrRwqjFY8V82lf4vipsR7rWK0jmNKgSKlEzYfy1EGZEqLG0DPYCwSQOi3+p9Inj/riIHL21WA4Sfweoe1eSV8CIKDKp1FYnKpNyUn60J2AOn9na9kFPrR/hepb9zZTBpaf3HO7pR4HcFYoIagGoSJEUlGRylvs63IMlyzJ7dJb4Lt2c+QJmg= 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: List-Subscribe: List-Unsubscribe: On Wed, Oct 22, 2025 at 11:34=E2=80=AFPM Huang, Ying wrote: > > Barry Song <21cnbao@gmail.com> writes: > > > On Wed, Oct 22, 2025 at 10:46=E2=80=AFPM Huang, Ying > > wrote: > > > >> > > >> > I agree. Yet the ish barrier can still avoid the page faults during = CPU0's PTL. > >> > >> IIUC, you think that dsb(ish) compared with dsb(nsh) can accelerate > >> memory writing (visible to other CPUs). TBH, I suspect that this is t= he > >> case. > > > > Why? In any case, nsh is not a smp domain. > > I think dsb(ish) will be slower than dsb(nsh) in theory. I guess that > dsb just wait for the memory write to be visible in the specified > shareability domain instead of making write faster. > > > I believe a dmb(ishst) is sufficient to ensure that the new PTE writes > > are visible > > dmb(ishst) (smp_wmb()) should pair with dmb(ishld) (smp_rmb()). > > > to other CPUs. I=E2=80=99m not quite sure why the current flush code us= es dsb(ish); > > it seems like overkill. > > dsb(ish) here is used for tlbi(XXis) broadcast. It waits until the page > table change is visible to the page table walker of the remote CPU. It seems we=E2=80=99re aligned on all points[1], although I=E2=80=99m not s= ure whether you have data comparing A and B. A: write pte don't broadcast pte tlbi don't broadcast tlbi with B: write pte broadcast pte tlbi don't broadcast tlbi I guess the gain comes from "don't broadcat tlbi" ? With B, we should be able to share many existing code. [1] https://lore.kernel.org/linux-mm/20251013092038.6963-1-ying.huang@linux= .alibaba.com/T/#m54312d4914c69aa550bee7df36711c03a4280c52 Thanks Barry