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b=KoggFrXtE+A9z2S7PNXRBnDwGytcKreECanzlrSvmX2VSnJ1UAHx8MALjzBO8dY6t c2wPZiuBM1q2adOP5QODYUkPyavxze2tzX6+ZBwN8eJTng9X/BtTk6DrOtF5+gqZr8 BWdgfjIYBqXzagN//hC+0OzTK1V9nRLQYL9bJwcc= Date: Tue, 13 Aug 2024 14:00:07 -0700 From: Andrew Morton To: Yu Zhao Cc: Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH mm-unstable v2] mm/hugetlb_vmemmap: batch HVO work when demoting Message-Id: <20240813140007.2459882ce674b45ecf1403f7@linux-foundation.org> In-Reply-To: <20240812224823.3914837-1-yuzhao@google.com> References: <20240812224823.3914837-1-yuzhao@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 9046880021 X-Rspamd-Server: rspam01 X-Stat-Signature: r9zgf756rnjmwipy5rnx6y1iuzcss6jc X-HE-Tag: 1723582812-271374 X-HE-Meta: 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 Toiyijx8 Urc+ZXaq2vvAgrYBzOvpfyRNXyyvucrh7QlKXk/LN+z6u0amPtKSwnCLxJ4B/mPT/D38ySa3EQWm0beTPgt8a4gfcfwz90xR01b8CG7zsZl/ESo3Nq5Dpvp7Z4tfVDJAfgAJW8YWEReLesnhrl+qlLct6QRSWP0F95AbSM0QqlqAfsVSJmTuFIKLjTY7kudfsS9fyAPU8uqZnn10egqzSo/aPiVfhmHtRPRgw3uJwxKA8+Y6q2TSFTvJ1KFw4bjIOiuYtJp/srOETzXrSErzFaSTIoUYhuMoXByocR3GwMKY23C4= 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 Mon, 12 Aug 2024 16:48:23 -0600 Yu Zhao wrote: > Batch the HVO work, including de-HVO of the source and HVO of the > destination hugeTLB folios, to speed up demotion. > > After commit bd225530a4c7 ("mm/hugetlb_vmemmap: fix race with > speculative PFN walkers"), each request of HVO or de-HVO, batched or > not, invokes synchronize_rcu() once. For example, when not batched, > demoting one 1GB hugeTLB folio to 512 2MB hugeTLB folios invokes > synchronize_rcu() 513 times (1 de-HVO plus 512 HVO requests), whereas > when batched, only twice (1 de-HVO plus 1 HVO request). And the > performance difference between the two cases is significant, e.g., > echo 2048kB >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote_size > time echo 100 >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote > > Before this patch: > real 8m58.158s > user 0m0.009s > sys 0m5.900s > > After this patch: > real 0m0.900s > user 0m0.000s > sys 0m0.851s That's a large change. I assume the now-fixed regression was of similar magnitude? > Note that this patch changes the behavior of the `demote` interface > when de-HVO fails. Before, the interface aborts immediately upon > failure; now, it tries to finish an entire batch, meaning it can make > extra progress if the rest of the batch contains folios that do not > need to de-HVO. > > Fixes: bd225530a4c7 ("mm/hugetlb_vmemmap: fix race with speculative PFN walkers") Do we think we should add this to 6.10.x? I do.