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SubjectRe: 2.4.8/2.4.9 VM problems

On Tue, 21 Aug 2001, Daniel Phillips wrote:

> On August 20, 2001 11:50 pm, Marcelo Tosatti wrote:
> > On Tue, 21 Aug 2001, Daniel Phillips wrote:
>
> > > If you've seen streaming IO pages getting evicted before being used,
> > > I'd like to know about it because something is broken in that case.
> >
> > I've seen the first page read by "swapin_readahead()" (which is the actual
> > page we want to swapin) be evicted _before_ we could actually use it (so
> > the read_swap_cache_async() call had to read the same page _again_ from
> > disk).
>
> It's not streaming IO, but whoops,

It does not matter. It just tells you that you're dropping pages too
early. That is even more valid for streaming IO.

I understand that having readahead pages to apply too much pressure
on really used pages is bad.

However, considering readaheaded pages as a "special case" (and drop them
previously, or whatever) will _always_ potentially fuckup streaming IO (so
yes, I think the old drop behind code is bad too).

> is that even with yesterday's SetPageReferenced patch to do_swap_page?

No. It will not help: the call to read_swap_cache_async() is before the
SetPageReferenced call.


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