Rik van Riel writes:
> The special cases in the use-once code have annoyed me for a while,
> and I'd like to see if replacing them with something simpler could
> be worthwhile.
>
> I haven't actually benchmarked (or even tested) this code yet, but
> the basic idea is that we want to ignore multiple references to the
> same page if they happen really close to each other, and only keep
> a page on the active list if it got accessed again on a time scale
> that matters to the pageout code. In other words, filtering out
> correlated references in a simpler way.
>
> Opinions ?
[...]
> - * active,unreferenced -> active,referenced
> */
> void fastcall mark_page_accessed(struct page *page)
> {
> - if (!PageActive(page) && PageReferenced(page) && PageLRU(page)) {
> - activate_page(page);
> - ClearPageReferenced(page);
> - } else if (!PageReferenced(page)) {
> + if (!PageReferenced(page))
> SetPageReferenced(page);
> - }
> }
So file system pages never get to the active list? Hmm... this doesn't
sound right.
>
> EXPORT_SYMBOL(mark_page_accessed);
> @@ -157,6 +149,7 @@ void fastcall lru_cache_add_active(struc
> if (!pagevec_add(pvec, page))
[...]
> goto keep_locked;
>
> referenced = page_referenced(page, 1, sc->priority <= 0);
> - /* In active use or really unfreeable? Activate it. */
> - if (referenced && page_mapping_inuse(page))
> +
> + if (referenced) {
> + /* New page. Let's see if it'll get used again... */
> + if (TestClearPageNew(page))
> + goto keep_locked;
> goto activate_locked;
> + }
This will screw scanning most likely: no referenced page is ever
reclaimed unless lowest scanning priority is reached---this looks like
sure way to oom and has capacity to increase CPU consumption
significantly.
>
> #ifdef CONFIG_SWAP
Nikita.
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