Date: Mon, 6 Jun 2005 01:05:51 -0400 From: Suleiman Souhlal <ssouhlal@FreeBSD.org> To: Scott Long <scottl@samsco.org> Cc: Maxim Sobolev <sobomax@portaone.com>, current@FreeBSD.org, fs@FreeBSD.org Subject: Re: [PATCH] IFS: Inode FileSystem Message-ID: <0A6C1F19-A734-4EC8-BE97-2D000D189968@FreeBSD.org> In-Reply-To: <42A3D6CF.2000504@samsco.org> References: <82ACAD58-B179-44E2-852F-60F25C0BBBC1@FreeBSD.org> <20050606033145.GA80739@www.portaone.com> <42A3D6CF.2000504@samsco.org>
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Hi, On Jun 6, 2005, at 12:53 AM, Scott Long wrote: > Maxim Sobolev wrote: > >> Are there any real users of this FS? If my memory serves, >> Adrian's plan was to add IFS support into the squid. I >> wonder if it had happened and whether or not it actually >> provides any real performance benefit. >> -Maxim >> > > IFS is centered around the observation that most apps already keep a > metamapping of 'filename ABC = data XYZ', where the filename is really > nothing more than a unique identifier for the data. Expressive > filenames and file hierachies are useful for humans, but matter > little to computers. The name "squid/cache/a/b/abc" has as much > meaning to a computer as the name "12345" (which might be the inode > number of the file). So taking this into account, you can strip > out all the overhead of recursive namei lookups, directory data reads, > directory hashing, etc, and just use the inode number directly as the > identifier for inodes. Looking up by inode is a O(1) operation > consisting of merely using the number to index into a inode array in a > particular cylinder group. It's a huge win for CPU overhead in the > filesystem, especially when we start talking about increasing the size > of m_links field and possibly going to 64-bit inode numbers. Talking about going to 64-bit inode numbers, how would we deal with the change in stat(2)? -- Suleiman Souhlal | ssouhlal@vt.edu The FreeBSD Project | ssouhlal@FreeBSD.org
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