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Wed, 22 Oct 2025 03:22:14 -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> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Wed, 22 Oct 2025 23:22:02 +1300 X-Gm-Features: AS18NWBircPFuACNmjNln0NVeJ5pMiUTEtaKbz7xy8k3SeBdgLEYQqjplgyUxCM 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-Server: rspam10 X-Rspamd-Queue-Id: 7751640003 X-Stat-Signature: dmdww5yzc3u4rufzw4qd44bzdpw4xnqb X-Rspam-User: X-HE-Tag: 1761128535-953161 X-HE-Meta: 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 Z2xBz8bk oMeGaLjt160ZiIM8= 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 10:55=E2=80=AFPM Barry Song <21cnbao@gmail.com> wro= te: > > 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 C= PU0'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 th= e > > case. > > Why? In any case, nsh is not a smp domain. > > I believe a dmb(ishst) is sufficient to ensure that the new PTE writes > are visible > to other CPUs. I=E2=80=99m not quite sure why the current flush code uses= dsb(ish); > it seems like overkill. On second thought, the PTE/page table walker might not be a typical SMP sync case, so a dmb may not be sufficient=E2=80=94we are not dealing with standard loa= d/store instruction sequences across multiple threads. In any case, my point is tha= t dsb(ish) might be slightly slower than your dsb(nsh), but it makes the PTE visible to other CPUs earlier and helps avoid some page faults after we=E2= =80=99ve written the PTE. However, if your current nsh version actually provides bet= ter performance=E2=80=94even when multiple threads may access the data simultan= eously=E2=80=94 It should be completely fine. Now you are write pte don't broadcast pte tlbi don't broadcast tlbi we might be: write pte broadcast pte tlbi don't broadcast tlbi Thanks Barry