On Tue, 11 Dec 2001, Marcelo Tosatti wrote:
> > I'll take a stab at completely removing the use-once stuff as an
> > emergency measure.
>
> Could you please make a patch without use-once and post the patch to
> lkml ?
>
> This way people can test it and report performance results.
OK, here's a quick hack to migrate 2.4 to second-chance
replacement. In this implementation that means:
1) for pages in the working set of processes, we keep
the pages resident whenever we find a referenced
bit in the page table
2) for pages which are not mapped, we unconditionally
move the page to the inactive list; the page only
gets reactivated if it is referenced while on the
inactive list
This should give us some small protection against use-once
data, since the referenced bit doesn't count, while allowing
us to protect the working set of processes.
It also makes shrinking of the slab-based filesystem caches
unconditional, to prevent bad effects there.
Note that I'm still compiling and haven't tested it yet,
please give it a spin.
regards,
Rik
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--- linux-2.4.17-pre8/mm/filemap.c.orig Tue Dec 11 16:11:16 2001 +++ linux-2.4.17-pre8/mm/filemap.c Tue Dec 11 16:27:44 2001 @@ -1249,23 +1249,20 @@ }
/* - * Mark a page as having seen activity. - * - * If it was already so marked, move it - * to the active queue and drop the referenced - * bit. Otherwise, just mark it for future - * action.. + * Simple second-chance replacement. + * As long as a page is on the active list, further references + * are ignored so used-once pages get replaced quickly. + * If a page on the inactive list gets referenced or has a + * referenced bit in the page table page, it gets moved back + * to the far end of the active list. */ void mark_page_accessed(struct page *page) { - if (!PageActive(page) && PageReferenced(page)) { + if (PageLRU(page) && !PageActive(page)) { activate_page(page); ClearPageReferenced(page); return; } - - /* Mark the page referenced, AFTER checking for previous usage.. */ - SetPageReferenced(page); }
/* --- linux-2.4.17-pre8/mm/swap.c.orig Tue Dec 11 16:11:16 2001 +++ linux-2.4.17-pre8/mm/swap.c Tue Dec 11 16:13:11 2001 @@ -59,7 +59,7 @@ { if (!TestSetPageLRU(page)) { spin_lock(&pagemap_lru_lock); - add_page_to_inactive_list(page); + add_page_to_active_list(page); spin_unlock(&pagemap_lru_lock); } } --- linux-2.4.17-pre8/mm/vmscan.c.orig Tue Dec 11 16:11:16 2001 +++ linux-2.4.17-pre8/mm/vmscan.c Tue Dec 11 16:43:10 2001 @@ -526,10 +526,14 @@
/* * This moves pages from the active list to - * the inactive list. + * the inactive list. If they get referenced + * while on the inactive list, they will be + * activated again. * - * We move them the other way when we see the - * reference bit on the page. + * Note that we cannot (and don't want to) + * clear the referenced bits in the page tables + * of pages, so the working sets of processes + * have an edge on cache pages. */ static void refill_inactive(int nr_pages) { @@ -542,15 +546,10 @@
page = list_entry(entry, struct page, lru); entry = entry->prev; - if (PageTestandClearReferenced(page)) { - list_del(&page->lru); - list_add(&page->lru, &active_list); - continue; - }
del_page_from_active_list(page); add_page_to_inactive_list(page); - SetPageReferenced(page); + ClearPageReferenced(page); } spin_unlock(&pagemap_lru_lock); } @@ -570,16 +569,16 @@ ratio = (unsigned long) nr_pages * nr_active_pages / ((nr_inactive_pages + 1) * 2); refill_inactive(ratio);
- nr_pages = shrink_cache(nr_pages, classzone, gfp_mask, priority); - if (nr_pages <= 0) - return 0; - shrink_dcache_memory(priority, gfp_mask); shrink_icache_memory(priority, gfp_mask); #ifdef CONFIG_QUOTA shrink_dqcache_memory(DEF_PRIORITY, gfp_mask); #endif
+ nr_pages = shrink_cache(nr_pages, classzone, gfp_mask, priority); + + if (nr_pages <= 0) + return 0; return nr_pages; }
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This archive was generated by hypermail 2b29 : Sat Dec 15 2001 - 21:00:21 EST