From owner-svn-src-head@freebsd.org Fri Oct 16 14:03:56 2015 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 869A6A16902 for ; Fri, 16 Oct 2015 14:03:56 +0000 (UTC) (envelope-from pfg@FreeBSD.org) Received: from nm3-vm0.bullet.mail.bf1.yahoo.com (nm3-vm0.bullet.mail.bf1.yahoo.com [98.139.212.154]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 3752C14EB for ; Fri, 16 Oct 2015 14:03:56 +0000 (UTC) (envelope-from pfg@FreeBSD.org) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s2048; t=1445004228; bh=VnUQJiuBvXj7yTM/r9l7XPJlG/W8/3ERiObqBbQUesY=; h=Subject:To:References:Cc:From:Date:In-Reply-To:From:Subject; b=rZVWjdw7+w7ojbboUg7OlKDdy6h2dBMCHywnern8y3twh//pCnJPfKXWs/rYZ1lCPzvlTbCod0qjQO944WlQzrklOd7kXphXmaJB2FwfaqcnNTt2ea9mrb0tI1SS+p/Ka3ONkUGkiG/BsaKGtIOI6SBfR8LI5UGzu/it6X4136SdcfnugxPsy/clnJXCZZC398c88xQ5XRagz2vxUDdcmofZjWHALT0rwwivIg76syK88CyzEFIMtwVitrpJN2QHoB6gy12JX5psgSH828/qgE9ft4pUgV0mCSQlzcBltv5jNcT4XGmA0BtXvgxFIz20QwZSphJw/f4mG8pPptKN7g== Received: from [98.139.170.179] by nm3.bullet.mail.bf1.yahoo.com with NNFMP; 16 Oct 2015 14:03:48 -0000 Received: from [68.142.230.78] by tm22.bullet.mail.bf1.yahoo.com with NNFMP; 16 Oct 2015 14:03:48 -0000 Received: from [127.0.0.1] by smtp235.mail.bf1.yahoo.com with NNFMP; 16 Oct 2015 14:03:48 -0000 X-Yahoo-Newman-Id: 697641.67357.bm@smtp235.mail.bf1.yahoo.com X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: ZToBMZUVM1m9DV2WWHydO_Kt2eRZupw1jYh7lJ95ZnxgdiD 1xdIZzFpAZcUzfmb12fTXdf0HvR8XYVytVHT0PvdQ9SoWwTzjIh4PC4r07jk vXRukcocROQU68SbIKaRUS8vq9J8zvYGXswnGkO97MITZH1lLNWjfGdbySNX kBqWpgtUcApiigYLcdTWB_E_1jG14CcVU_2_2JHGKUOnEdsJWCSQz8ZswacQ jvP0suJXVMCKwqIV2nZWRORuVmDsw744BEn3EFIXA5wNRE3tmjvRfzoOVioM y3ptiRcdfUjIIK_ZmQsar6OZ56dae3L6X6QtdUkHeT8vPj.YWeWks3MvsTEP d8pRYvfQ9dql91ADVSNo76jrSJvaDLPhJVm.DS3gJbTDFkL.avL6uqCqho9Q tKumr7snXju50nJh4GVU3tK8IF9RHyR71irvSDSq8mmtaHIbKZMOw._Y2Exs W4MjAIcRe9xcTxoNXpgt.0SFxdpokK9hBuReI6wSOGfn033W5eyV.qPpVxEV mj7GKBpL7fMaTUJBHE1Lo2IM.ymD6Urt2 X-Yahoo-SMTP: xcjD0guswBAZaPPIbxpWwLcp9Unf Subject: Re: svn commit: r289405 - head/sys/ufs/ffs To: Bruce Evans , Hans Petter Selasky References: <201510160306.t9G3622O049128@repo.freebsd.org> <20151016151349.W1280@besplex.bde.org> <5620B15C.8090104@selasky.org> <20151016194242.N2138@besplex.bde.org> Cc: Warner Losh , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org From: Pedro Giffuni Message-ID: <562103B6.2090406@FreeBSD.org> Date: Fri, 16 Oct 2015 09:03:34 -0500 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20151016194242.N2138@besplex.bde.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 Oct 2015 14:03:56 -0000 On 10/16/15 03:53, Bruce Evans wrote: > On Fri, 16 Oct 2015, Hans Petter Selasky wrote: > >> On 10/16/15 08:21, Bruce Evans wrote: >>> [Bruce Evans didn't write:] >>> In addition, making the file contiguous in LBA space doesn't >>> improve the access times from flash devices because they have no seek >>> time. >> >> This is not exactly true, like Bruce pointed out too. Maybe there >> should be a check, that if the block is too small reallocate it, else >> leave it for the sake of the flash. Doing 1K accesses versus 64K >> accesses will typically show up in the performance benchmark >> regardless of how fast the underlying medium is. > > Now I don't unerstand the whole point of the change. Anything that reduces > i/o's is good, but AFAIK ffs_doreallocblks() is all in software. Writes > should be delayed so that it doesn't have to do extra i/o's to back out of > committed writes. Often it reduces the number of writes and increases > their size by making blocks contiguous so that the write can be clustered. > Increasing the write size is especially good for flash devices, but maybe > ffs's default block size is already large enough. > I agree with Bruce: reallocation (which our ext2fs also does) happens in memory, before it hits the disk. By the nature of their load, Netflix doesn't care about fragmentation, but even in that case reallocblk doesn't hurt, and I don't see anything inherent in SSDs that makes fragmentation desirable. Of course, no one understands reallocblk better than Kirk, and Warner knows SSD's pretty well so I must be missing something. :). Pedro.