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Date:      Thu, 5 Sep 1996 16:51:25 +0900 (KST)
From:      Heo Sung-Gwan <heo@cslsun10.sogang.ac.kr>
To:        freebsd-hackers@FreeBSD.ORG
Subject:   Questions about cluster read buffer cache
Message-ID:  <Pine.SUN.3.93.960905164903.19739A-100000@cslsun10>

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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
 




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