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List:       linux-kernel
Subject:    Re: clustering page-ins
From:       Chuck Lever <cel () monkey ! org>
Date:       1999-08-10 22:57:04
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On Fri, 6 Aug 1999, Jamie Lokier wrote:
> Intuitively I'd go for clearing the "accessed" bits on all ptes you fill
> in except the one that really faulted.
> 
> Conclusion: I don't think you should put it in do_no_page.  Rather,
> write a new function preload_page in memory.c, and have filemap_nopage
> call that for each page in a cluster that is a cache hit during the
> read-ahead scan.
> 
> preload_page() should duplicate some of the code in do_no_page(): it
> should fill in a pte, but only if the pte is "not present" already, and
> the new pte should be marked "old" not "young".  If any memory
> allocation is required (for pgds and pmds) it should simply return
> without doing the allocation.

actually, i think you'd want to do just the opposite.  allocating the
extra pmds and ptes during read-ahead is exactly what you want to do,
while diddling the entries in already existing pte's will just break page
faulting in subtle ways.

so i see two different approaches.  1 is minimal, and leaves the existing
code intact, while 2 substantially changes generic file mapping.

1.  pre-allocate pte's during read-ahead, and do read-ahead just as we've
discussed.

2.  fault in and map in entire clusters at a time.  if the page fault
happens on the first page in a cluster, then watch for sequential cluster
faults, and do read-ahead.

	- Chuck Lever
--
corporate:	<chuckl@netscape.com>
personal:	<chucklever@netscape.net> or <cel@monkey.org>

The Linux Scalability project:
	http://www.citi.umich.edu/projects/linux-scalability/


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