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SubjectRe: [patch] swap-speedup-2.4.3-B3 (fwd)
On Thu, 26 Apr 2001, Rik van Riel wrote:

> On Thu, 26 Apr 2001, Mike Galbraith wrote:
>
> > > > > No. It livelocked on me with almost all active pages exausted.
> > > > Misspoke.. I didn't try the two mixed. Rik's patch livelocked me.
> > >
> > > Interesting. The semantics of my patch are practically the same as
> > > those of the stock kernel ... can you get the stock kernel to
> > > livelock on you, too ?
> >
> > Generally no. Let kswapd continue to run? Yes, but not always.
>
> OK, then I guess we should find out WHY the thing livelocked...

Hi Rik,

I decided to take a break from pondering input and see why the thing
ran itself into the ground. Methinks I was sent the wrooong patch :)

--- linux-2.4.4-pre7/mm/vmscan.c.orig Wed Apr 25 23:59:48 2001
+++ linux-2.4.4-pre7/mm/vmscan.c Thu Apr 26 00:31:31 2001
@@ -24,6 +24,8 @@

#include <asm/pgalloc.h>

+#define MAX(a,b) ((a) > (b) ? (a) : (b))
+
/*
* The swap-out function returns 1 if it successfully
* scanned all the pages it was asked to (`count').
@@ -631,17 +633,45 @@
/**
* refill_inactive_scan - scan the active list and find pages to deactivate
* @priority: the priority at which to scan
- * @oneshot: exit after deactivating one page
+ * @count: the number of pages to deactivate
*
* This function will scan a portion of the active list to find
* unused pages, those pages will then be moved to the inactive list.
*/
-int refill_inactive_scan(unsigned int priority, int oneshot)
+int refill_inactive_scan(unsigned int priority, int count)
{
struct list_head * page_lru;
struct page * page;
- int maxscan, page_active = 0;
- int ret = 0;
+ int maxscan = nr_active_pages >> priority;
+ int page_active = 0;
+
+ /*
+ * If no count was specified, we do background page aging.
+ * This is done so, after periods of little VM activity, we
+ * know which pages to swap out and we can handle load spikes.
+ * However, if we scan unlimited and deactivate all pages,
+ * we still wouldn't know which pages to swap ...
+ *
+ * The obvious solution is to do less background scanning when
+ * we have lots of inactive pages and to completely stop if we
+ * have tons of them...
+ */
+ if (!count) {
+ int nr_active, nr_inactive;
+
+ /* Active pages can be "hidden" in ptes, take a saner number. */
+ nr_active = MAX(nr_active_pages, num_physpages / 2);
+ nr_inactive = nr_inactive_dirty_pages + nr_free_pages() +
+ nr_inactive_clean_pages();
+
+ if (nr_inactive * 10 < nr_active) {
+ maxscan = nr_active_pages >> 4;
+ } else if (nr_inactive * 3 < nr_active_pages) {
+ maxscan = nr_active >> 8;
+ } else {
+ maxscan = 0;
+ }
+ }

/* Take the lock while messing with the list... */
spin_lock(&pagemap_lru_lock);
@@ -690,14 +720,13 @@
list_del(page_lru);
list_add(page_lru, &active_list);
} else {
- ret = 1;
- if (oneshot)
+ if (--count <= 0)
break;
}
}
spin_unlock(&pagemap_lru_lock);

- return ret;
+ return count;
}

/*
@@ -805,10 +834,9 @@
schedule();
}

- while (refill_inactive_scan(DEF_PRIORITY, 1)) {
- if (--count <= 0)
- goto done;
- }
+ count -= refill_inactive_scan(DEF_PRIORITY, count);
+ if (--count <= 0)
+ goto done;

/* If refill_inactive_scan failed, try to page stuff out.. */
swap_out(DEF_PRIORITY, gfp_mask);

-
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