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t=1794256608; bh=9oF9audfKANIUeCSjRE2UxoYSJ8eZS3TN4Enjb9NBvA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EefOnyi2juZx4CLNe0tV/hc9vymdy866x18Xt0oh0y/RHhUiC1T/CW9gCl5MSPyyt bf9WQ0uqfn2sToC15cCy7r5Bpgb7yZAhbXviQsZDSb8Snt77HjRuBbGMQ51iw4pC56 oBPeCrcM2GaD75nLGNISe9o9KeKQ/Ysd4A3crHHnGBXct/ilMTser/ljPM67RbVuO5 GwWwD1mG0kaH2gncGE4ZZo80n8bW3zDa95/z85GZkgJqJExJlZssZjcxtQLmefRWTA 2HtvvweWAAE5dQ9cqHshfsygxx8LjajMIFFzEQYTVLhmOuDgPmQqvQKtSQdJIQahuy mBAA7yyrGQMYg== Message-ID: <3a137aa0-d0b5-4267-b64c-d58ab4235603@kernel.org> Date: Mon, 9 Nov 2026 21:36:40 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/migrate: don't batch the TLB flush when there is nothing to batch To: Zhiteng Qiu Cc: Andrew Morton , Ying Huang , Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Alistair Popple , Xin Hao , Dave Hansen , Yuan Zhong , Shifei Ge , Jianyong Wu , Shijie Huang , Yibin Liu , Fengyu Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261106041628.1177963-1-qiuzhiteng@hygon.cn> <20261107143456.1590658-1-qiuzhiteng@hygon.cn> <20261109122915.2150586-1-qiuzhiteng@hygon.cn> <20261110001816.2186986-1-qiuzhiteng@hygon.cn> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: m1ehqzrcuo8t5f35dp9xszreso1qwidj X-Rspamd-Queue-Id: 1984640004 X-Rspam-User: X-Rspamd-Server: rspam11 X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1794256609-984330 X-HE-Meta: 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 ch9HuWwJ YE7FaNZf43CmavVzuRZ5q5uY4L4V/+AE4QGPXgzbeU1BhghBcQUuINZOJNBFMVvf92CnXvoTcfG0mqkpNCUTeISo8Sa2u1ISX7Vl84wUwatOK18ddIZ3gV7zov7zcLKO0sNhENMYXwh0aH8/weYqcxlgkfEHzrdaN53r1MUcs9WxGfCErbX458pEKsPzEKZnN/mcQNYmgr0zrU3E3OCWAczZ7pHX0I2LqwA58vvCo8VBkMDeOFI6o7C4+8/JPnUOg1oJgnlO7kyg3hl+9SeS9N5/lS+pFlFwNGMs8jEcASTa3C59JwOd4ZNiJHBC9657nUqlqpJj2n1ul+MxbBPBSrs9SPw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/9/26 17:18, Zhiteng Qiu wrote: > On 11/9/26 14:07, David Hildenbrand (Arm) wrote: >> For the future, please don't send new revisions in reply to old revisions. > > Sorry about that. I'll send the next revision as a new thread. > >> Is there no way to avoid that boolean? > > [...] > >> This is all information the caller could provide, and the caller could just >> provide the TTU flag then instead of passing a new "bool". >> >> Also, likely this check can be put into a separate helper function. > > Agreed. I'll move the decision into a helper called from > migrate_pages_batch() and pass the resulting flags to > migrate_folio_unmap(). > >> I am not quite happy about the folio_mapcount() check, though: as soon as we >> optimize try_to_unmap() to batch better for large folios, it would be just plain >> wrong. > > That makes sense. A large folio's mapcount alone would not tell us > how many separate flushes are needed once its PTEs can be handled > in a batch. > > Would it make sense to restrict the optimization to a single, > singly mapped small folio and keep batching for all large folios, > as in the scope of v2? The changelog performance numbers were > measured with the v2 check. Or do you have a different direction > in mind? Likely best to focus on small folios first. -- Cheers, David