Re: [PATCH][5/?] count writeback pages in nr_scanned

[Andrew Morton]

Andrea Arcangeli <andrea@xxxxxxx> wrote:
>
> The fix is very simple and it is to call wait_on_page_writeback on one
>  of the pages under writeback.

eek, no.  That was causing waits of five seconds or more.  Fixing this
caused the single greatest improvement in page allocator latency in early
2.5.  We're totally at the mercy of the elevator algorithm this way.

If we're to improve things in there we want to wait on _any_ eligible page
becoming reclaimable, not on a particular page.
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