Messages in this thread |  | | Date | Fri, 28 Sep 2001 17:14:44 -0300 (BRST) | From | Rik van Riel <> | Subject | Re: 2.4.10 does not set accessed bit for readahead pages |
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On Fri, 28 Sep 2001, Marcelo Tosatti wrote:
> NOTE: I'm saying that it is _bad_ to throw away readahead pages > easily because I've seen it in practice. I'll try to test this > in real practice again soon (not this week) to make sure. > > Comments ?
Setting the referenced bit on not (yet) used readahead pages could have the damaging side effect of swapping out pages from the working set in preference to the readahead pages.
OTOH, without some special trick for linear access the VM will prefer to swap out the pages we're about to use (the readahead pages) instead of the pages we just used -- the absolute worst thing for sequential IO.
One simple solution which achieves both the effect of dropping the right pages in a sequential IO stream and making sure that not-used readahead pages aren't pushing out the working set would be drop-behind.
I know drop-behind isn't the prettiest thing, but it's simple and it works.
regards,
Rik -- IA64: a worthy successor to the i860.
http://www.surriel.com/ http://www.conectiva.com/ http://distro.conectiva.com/
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