Re: 2.4.23aa2 (bugfixes and important VM improvements for the highend)

[Nikita Danilov]

Rik van Riel writes:

[...]

 > 
 > Duh, I forgot all about the rotate_reclaimable_page() stuff.
 > That may well fix all problems 2.6 would have otherwise had
 > in this area.
 > 
 > I really hope we won't need anything like the O(1) VM stuff
 > in 2.6, since that would leave me more time to work on other
 > cool stuff (like resource management ;)).

Page-out from end of the inactive list is not efficient, because pages
are submitted for IO in more or less random order and this results in
a lot of seeks. Test-case: replace ->writepage() with

int foofs_writepage(struct page *page)
{
        SetPageDirty(page);
        unlock_page(page);
        return 0;
}

and run

$ time cp /tmpfs/huge-data-set /foofs

File systems (and anonymous memory) want clustered write-out and VM
designs with separate write-out queue (like O(1) VM) are better suited
for this.

Nikita.
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