Re: Thoughts about streaming from disk and VM
Re: Thoughts about streaming from disk and VM
- Subject: Re: Thoughts about streaming from disk and VM
- From: Bill Stewart <email@hidden>
- Date: Thu, 13 Mar 2003 12:32:27 -0800
On Thursday, March 13, 2003, at 01:32 AM, Herbie Robinson wrote:
At 1:02 PM -0600 3/12/03, Eric Huffman wrote:
Multiple Files (VM) -
Under a VM OS, the above approach for multiple files seems to have
non-optimal runtime behavior since the VM manager has to perform
additional memory management for the buffer memory (e.g. possibly
paging
out memory for the allocation of the buffers, possibly paging in the
buffers if they were paged out since the last file IO, and possibly
paging out the buffers after the file IO).
I haven't actually tried this in OS X; so, I may be blowing smoke, but
many Unix implementations optimize the case where the memory and disk
addresses both start on a page boundary.
Yes INDEED - you will get much better disk performance if the following
are page aligned:
(1) The start address of your buffer
(2) the num bytes you read or write to that buffer
(3) the offset within the file itself that you are reading or writing
to.
In short - if all three are page aligned you win...
Bill
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