lkml.org 
[lkml]   [2007]   [Sep]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] prevent kswapd from freeing excessive amounts of lowmem
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 <riel@redhat.com>
>
>> --- 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.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-09-08 22:23    [W:0.090 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site