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[209.85.220.65]) by mx.google.com with SMTPS id z1sor4826208pjn.1.2019.06.11.18.27.12 for (Google Transport Security); Tue, 11 Jun 2019 18:27:12 -0700 (PDT) Received-SPF: pass (google.com: domain of nadav.amit@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=agp8Ljxg; spf=pass (google.com: domain of nadav.amit@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=CtAUnKccNVM3Ar1NimuBm5cYjQQHpUUV35G3NGl7I18=; b=agp8LjxgsiKUNBRzMQ6B1lsikXTP9MXAxScOYcZnsKclD0N+jlNVoUl/hzW4poyT5e 3L5Kpn7BSqpfe4Vqr0OMLbW+npbpmydrSh4Nk6mj5SGyx5Jj6jf653H8VmcdoFa5nFlP PVXiNmiBrwZEiKboElbWiL4LdjFKAAbWcoG28ZIwtcy8dPhR9hlh49PJ6xikrmMZLHzP 20qVkn6ttaCMzY1I08lsTIN5eoleBIFYn7aRuLf/OzGJBwoDwiiv7JFIo5WL8ooodEKt b/SI9mnoX3vTwRgRrKm2an9+aTc8TPah2tNonQDJrq5z+DrzQV1yJmuEkhrXeIPbcuOQ mhuw== X-Google-Smtp-Source: APXvYqyJ4j/UPWrjvOrQasPCqbyNI8I79UTnDUErLKqAMrK1NLwjt0JJmzYLlyxhcupMkfrOP1908w== X-Received: by 2002:a17:90a:cb87:: with SMTP id a7mr10403544pju.130.1560302831475; Tue, 11 Jun 2019 18:27:11 -0700 (PDT) Received: from [10.2.189.129] ([66.170.99.2]) by smtp.gmail.com with ESMTPSA id c10sm3547108pjq.14.2019.06.11.18.27.10 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 11 Jun 2019 18:27:10 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.11\)) Subject: Re: [PATCH 16/16] mm: pass get_user_pages_fast iterator arguments in a structure From: Nadav Amit In-Reply-To: <1560300464.nijubslu3h.astroid@bobo.none> Date: Tue, 11 Jun 2019 18:27:09 -0700 Cc: Rich Felker , "David S. Miller" , James Hogan , Paul Burton , Linus Torvalds , Yoshinori Sato , Andrey Konovalov , Benjamin Herrenschmidt , Khalid Aziz , LKML , linux-mips@vger.kernel.org, Linux-MM , linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, Michael Ellerman , Paul Mackerras , sparclinux@vger.kernel.org, the arch/x86 maintainers Content-Transfer-Encoding: 7bit Message-Id: <0441EC80-B09F-4722-B186-E42EB6A83386@gmail.com> References: <20190611144102.8848-1-hch@lst.de> <20190611144102.8848-17-hch@lst.de> <1560300464.nijubslu3h.astroid@bobo.none> To: Nicholas Piggin , Christoph Hellwig X-Mailer: Apple Mail (2.3445.104.11) 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: > On Jun 11, 2019, at 5:52 PM, Nicholas Piggin wrote: > > Christoph Hellwig's on June 12, 2019 12:41 am: >> Instead of passing a set of always repeated arguments down the >> get_user_pages_fast iterators, create a struct gup_args to hold them and >> pass that by reference. This leads to an over 100 byte .text size >> reduction for x86-64. > > What does this do for performance? I've found this pattern can be > bad for store aliasing detection. Note that sometimes such an optimization can also have adverse effect due to stack protector code that gcc emits when you use such structs. Matthew Wilcox encountered such a case: https://patchwork.kernel.org/patch/10702741/