Date: Fri, 16 May 1997 12:58:01 -0500 (EST) From: "John S. Dyson" <toor@dyson.iquest.net> To: terry@lambert.org (Terry Lambert) Cc: dyson@FreeBSD.ORG, james@westongold.com, freebsd-hackers@FreeBSD.ORG Subject: Re: mmap() Message-ID: <199705161758.MAA02020@dyson.iquest.net> In-Reply-To: <199705161744.KAA17629@phaeton.artisoft.com> from Terry Lambert at "May 16, 97 10:44:41 am"
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> > Okay!!! Firstly, the FFS FS dependent VOP_GETPAGES does do read-aheads iff > > the object is marked with MADV_SEQUENTIAL. Secondly, it would be fairly > > easy to detect sequential behavior automatically. Right now, there are > > much bigger fish to fry!!! :-) (The reason that it is in the FS dependent > > code, is that it is only optional that one uses the cluster read ahead > > code on a per filesystem basis.) It is likely that the FFS dependent > > VOP_GETPAGES code will work with other filesystem types (perhaps with > > minor mods.) > > It seems to me that the OBJ_SEQUENTIAL blocks the VOP_GETPAGE() caller > until all pages have been faulted, instead of asynchronously doing the > pages following the requested page, and returing immediately for the > requested page. This would introduce "bursty" behaviour, as sequential > access would incur a large latence for every read-ahead trigger. > The read-ahead isn't blocked for in that case. It only waits for the blocks that have been explicitly requested. John
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