Pavel Machek wrote:
Hi!
The current VM can get itself into trouble fairly easily
on systems
with a small ZONE_HIGHMEM, which is common on i686
computers with
1GB of memory.
On one side, page_alloc() will allocate down to
zone->pages_low,
while on the other side, kswapd() and balance_pgdat()
will try
to free memory from every zone, until every zone has
more free
pages than zone->pages_high.
Highmem can be filled up to zone->pages_low with page
tables,
ramfs, vmalloc allocations and other unswappable things
quite
easily and without many bad side effects, since we still
have
a huge ZONE_NORMAL to do future allocations from.
However, as long as the number of free pages in the
highmem
zone is below zone->pages_high, kswapd will continue
swapping
things out from ZONE_NORMAL, too!
Sami Farin managed to get his system into a stage where
kswapd
had freed about 700MB of low memory and was still "going
strong".
The attached patch will make kswapd stop paging out data
from
zones when there is more than enough memory free. We do
go above
zone->pages_high in order to keep pressure between zones
equal
in normal circumstances, but the patch should prevent
the kind
of excesses that made Sami's computer totally unusable.
Please merge this into -mm.
Signed-off-by: Rik van Riel <[email protected]>
--- linux-2.6.22.noarch/mm/vmscan.c.excessive 2007-09-05 12:19:49.000000000 -0400
+++ linux-2.6.22.noarch/mm/vmscan.c 2007-09-05 12:21:40.000000000 -0400
@@ -1371,7 +1371,13 @@ loop_again:
temp_priority[i] = priority;
sc.nr_scanned = 0;
note_zone_scanning_priority(zone, priority);
- nr_reclaimed += shrink_zone(priority, zone, &sc);
+ /*
+ * We put equal pressure on every zone, unless one
+ * zone has way too many pages free already.
+ */
That does not seem right. Having empty HIGHMEM and full LOWMEM would
be very bad, right? We may stop freeing when there's enough LOWMEM
free, but not if there's only HIGHMEM free.
Please read the code this patch applies to.
The check I add conditionalizes the individual
calls to shrink_zone(), so we do not call
shrink_zone() for a zone that has a ton of free
pages. We still call shrink_zone() for the
other zones.
--
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is. Each group
calls the other unpatriotic.
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