Date: Fri, 29 Oct 2010 18:05:26 +0300 From: Andriy Gapon <avg@icyb.net.ua> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-stable@freebsd.org, Alexander Zagrebin <alexz@visp.ru> Subject: Re: 8.1-STABLE: zfs and sendfile: problem still exists Message-ID: <4CCAE2B6.1050906@icyb.net.ua> In-Reply-To: <20101029145349.GX2392@deviant.kiev.zoral.com.ua> References: <4CCACDC0.7050802@icyb.net.ua> <1BDB4D1B02274CC8AA2DD5E68190CB5D@vosz.local> <20101029145349.GX2392@deviant.kiev.zoral.com.ua>
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on 29/10/2010 17:53 Kostik Belousov said the following: > Could it be the priming of the vm object pages content ? Sorry, not familiar with this term. Do you mean prepopulation of vm object with valid pages? > Due to double-buffering, and (possibly false) optimization to only What optimization? > perform double-buffering when vm object already has some data cached, > reads can prime vm object page list before file is mmapped or > sendfile-ed. > No double-buffering is done to optimize anything. Double-buffering is a consequence of having page cache and ARC. The special "double-buffering code" is to just handle that fact - e.g. making sure that VOP_READ reads data from page cache instead of ARC if it's possible that the data in them differs (i.e. page cache has more recent data). So, if I understood the term 'priming' correctly, no priming should ever occur. -- Andriy Gapon
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