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AJvYcCUn8eES5PDu1ibuCzHlRbAPZsIDc1gFctLFDNUM1jsnealOGHhaMnoLpub1z4OuiYnHjTxXe/tYoA==@kvack.org X-Gm-Message-State: AOJu0Yw99JVz+yXyDUfm1yHXBZDa7jm4BbrUqxpj5DFQYm3/3r1Plc58 JPaJ35bBlHBeadbULyAvx0xHe8sCURlVmRgAKCwHV7tW/NRD+WID8CTjmBYVW/Azu+/qnY14Igj bp/np0sMznnlo6Q04MHuzysCDbdU= X-Google-Smtp-Source: AGHT+IEco3mpy6nEBSUmTveZo0x92eIDjxuFcIiyK5ye00+STTQi8OyJyA5UjcuSlxksxvMXpIs9CBuE5eBjlMppUJc= X-Received: by 2002:a05:6402:2554:b0:5c4:1c89:6e36 with SMTP id 4fb4d7f45d1cf-5c41c896e4emr14866442a12.19.1726544185660; Mon, 16 Sep 2024 20:36:25 -0700 (PDT) MIME-Version: 1.0 References: <20240913091902.1160520-1-dev.jain@arm.com> In-Reply-To: From: Lance Yang Date: Tue, 17 Sep 2024 11:35:48 +0800 Message-ID: Subject: Re: [PATCH] mm: Compute mTHP order efficiently To: Matthew Wilcox , Barry Song , dev.jain@arm.com Cc: akpm@linux-foundation.org, david@redhat.com, ryan.roberts@arm.com, anshuman.khandual@arm.com, hughd@google.com, wangkefeng.wang@huawei.com, baolin.wang@linux.alibaba.com, gshan@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: 22AD9160012 X-Rspamd-Server: rspam01 X-Stat-Signature: 4i7ygy15pid5br6qm8tt7hqm3coy7i9u X-HE-Tag: 1726544187-421985 X-HE-Meta: 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 9REszubh o333kM7BTMUEaK5SLHxPFInqVtxXOT5wg3uqQUkKUbHeLS11qZXz7eOhA9fB3r4oCmrtTpiUXmCbbxOC66SQJhhRfg9JmLmfrBxeIuYra3ccYOL128HAc6BzrdrJ47jVNt//GEBv4mGBtUCXajS6NR8LSNmmZD5vsftT86wINBby91amlm2rzC+C0QTPs8jG3jxIWHEooOaFu0lc0UFyaMFn69AMlyu6FQXiAyiP6kZK3c7a8OBLmwDazWQZmX8TYiMd8ecfyDZ+Wc6RaWbRSKLQFuyZSztKA5bU8cjtC4lcPjsEgakEcjUkVgYyrQ/y28LLQpfeXt1h4hN2FGsnEUOXFPLZ5MKq6HqDr45wkqdsmbvQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.001773, 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, Sep 16, 2024 at 9:25=E2=80=AFPM Matthew Wilcox wrote: > > On Fri, Sep 13, 2024 at 02:49:02PM +0530, Dev Jain wrote: > > We use pte_range_none() to determine whether contiguous PTEs are empty > > for an mTHP allocation. Instead of iterating the while loop for every > > order, use some information, which is the first set PTE found, from the > > previous iteration, to eliminate some cases. The key to understanding > > the correctness of the patch is that the ranges we want to examine > > form a strictly decreasing sequence of nested intervals. > > This is a lot more complicated. Do you have any numbers that indicate > that it's faster? Yes, it's fewer memory references, but you've gone > from a simple linear scan that's easy to prefetch to an exponential scan > that might confuse the prefetchers. +1 I'm not sure if multiple mthp sizes will be enabled for common cases ;) If not, this could be a bit more complicated, IMO. @Barry, could you share whether OPPO typically uses multiple mthp sizes in their scenarios? Thanks, Lance