On Mon, 10 Dec 2001, Rik van Riel wrote:
> On Mon, 10 Dec 2001, Andrew Morton wrote:
>
> > A fix may be to just remove the use-once stuff. It is one of the
> > sources of this problem, because it's overpopulating the inactive list.
>
> Absolutely. Use-once is an inherently unstable system, suitable
> for things like a database load (where you know you want to spend
> a certain percentage of your RAM on caching the index), but not
> suitable for a general-purpose VM, where you have no idea how
> large the working set will be.
>
> I'll take a stab at completely removing the use-once stuff as an
> emergency measure.
Rik,
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.
I really would prefer to remove use-once as I also think its an
optimization which breaks some workloads, but I want to know what happens
in practice if we do that.
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;
}