From owner-freebsd-hackers Thu Sep 5 00:57:12 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id AAA29605 for hackers-outgoing; Thu, 5 Sep 1996 00:57:12 -0700 (PDT) Received: from ccs.sogang.ac.kr (ccs.sogang.ac.kr [163.239.1.1]) by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id AAA29359 for ; Thu, 5 Sep 1996 00:52:43 -0700 (PDT) Received: from cslsun10.sogang.ac.kr by ccs.sogang.ac.kr (8.7.5/Sogang) id QAA06378; Thu, 5 Sep 1996 16:48:46 +0900 (KST) Received: from localhost by cslsun10.sogang.ac.kr (4.1/SMI-4.1) id AA19762; Thu, 5 Sep 96 16:51:26 KST Date: Thu, 5 Sep 1996 16:51:25 +0900 (KST) From: Heo Sung-Gwan X-Sender: heo@cslsun10 To: freebsd-hackers@FreeBSD.ORG Subject: Questions about cluster read buffer cache Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk Hi, I have some questions about cluster read-ahead buffer cache. When a file is read sequentially, one cluster is always prefetched that is not requested yet. At least vp->v_ralen blocks are already in buffer. If the difference between the most recently accessed block and the most recently prefetched block is greater than vp->v_ralen, next cluster is read ahead into buffer. During reading a file sequentially the value of vp->v_ralen is 7. Why is it? And if the blocks in a cluster is requested before the completion of asynchronous read-ahead of the cluster, how is this situation handled? Which part of vfs_cluster.c does handle this? -- Heo Sung-Gwan O.S. Lab. Dept. of Computer Science, Sogang University, Seoul, Korea. E-mail: heo@oslab.sogang.ac.kr