:
:ask for 8k, but the system will fetch the next 64k of data. Problem is
:the system does nothing until you read the next 8k past the 64k
:alreqady read in, then it jumps up and grabs the next 64k. You're
:still waiting on I/O every 8th read. Ideally it would do an async
:..
:--
: Dan Nelson
: [EMAIL PROTECTED]
No, this isn't true. The system places a marker 8K or 16K before the
last read block and initiates the next read-ahead before you exhaust the
first one.
For mapped data the system intentionally does not map the page table entry
for a page or two before the end of the read ahead in order to force a
page fault so it can initiate the next read ahead.
For read data the system marks a buffer near the end of the read ahead
so when read encounters it the system knows to queue then next read-ahead.
Also, for that matter, remember that the hard drives themselves generally
cache whole tracks and do their own read-ahead. This is why dd'ing a
large file usually results in the maximum transfer rate the hard drive
can do.
-Matt
Matthew Dillon
<[EMAIL PROTECTED]>
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