Messages in this thread |  | | | Date | Thu, 19 Jan 2006 17:03:05 -0800 | | From | Andrew Morton <> | | Subject | Re: Out of Memory: Killed process 16498 (java). |
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Dave Jones <davej@redhat.com> wrote: > > On Thu, Jan 19, 2006 at 03:11:45PM -0000, Andy Chittenden wrote: > > DMA free:20kB min:24kB low:28kB high:36kB active:0kB inactive:0kB > > present:12740kB pages_scanned:4 all_unreclaimable? yes > > Note we only scanned 4 pages before we gave up. > Larry Woodman came up with this patch below that clears all_unreclaimable > when in two places where we've made progress at freeing up some pages > which has helped oom situations for some of our users. >
We already clear ->all_unreclaimable in free_pages_bulk, so I guess the changes here are a) bypass the per-cpu-pages magazining (fair enough I suppose) and b) clear all_unreclaimable earlier: as a page becomes reclaimable, not as we reclaim it.
I wonder if it really makes a difference. Given that various processes are currently scanning their little hearts out, if a reclaimable page pops up at the tail of the LRU, we'll reclaim it pretty much immediately and go off and, after the per-cpu batching, will clear ->all_unreclaimable.
> --- linux-2.6/mm/filemap.c~ 2005-12-10 01:47:15.000000000 -0500 > +++ linux-2.6/mm/filemap.c 2005-12-10 01:47:46.000000000 -0500 > @@ -471,11 +471,18 @@ EXPORT_SYMBOL(unlock_page); > */ > void end_page_writeback(struct page *page) > { > + struct zone *zone = page_zone(page); > if (!TestClearPageReclaim(page) || rotate_reclaimable_page(page)) { > if (!test_clear_page_writeback(page)) > BUG(); > } > smp_mb__after_clear_bit(); > + if (zone->all_unreclaimable) { > + spin_lock(&zone->lock); > + zone->all_unreclaimable = 0; > + zone->pages_scanned = 0; > + spin_unlock(&zone->lock); > + } > wake_up_page(page, PG_writeback); > }
Wouldn't it be better to only clear ->all_unreclaimable if the page was actually reclaimable? ie: inside rotate_reclaimable_page()?
Doing that would also fix the deadlock in the above code: zone.lock is supposed to be irq-safe.
> EXPORT_SYMBOL(end_page_writeback); > --- linux-2.6.15/mm/page_alloc.c~ 2006-01-09 13:40:03.000000000 -0500 > +++ linux-2.6.15/mm/page_alloc.c 2006-01-09 13:40:50.000000000 -0500 > @@ -722,6 +722,11 @@ static void fastcall free_hot_cold_page( > if (pcp->count >= pcp->high) { > free_pages_bulk(zone, pcp->batch, &pcp->list, 0); > pcp->count -= pcp->batch; > + } else if (zone->all_unreclaimable) { > + spin_lock(&zone->lock); > + zone->all_unreclaimable = 0; > + zone->pages_scanned = 0; > + spin_unlock(&zone->lock); > }
This is the bypass-the-batching patch. It's a reasonable thing to do, but I'd just do it unconditionally and remove the code which clears ->all_unreclaimable from free_pages_bulk(), if possible.
Has this patch been shown to have any effect? If so, what was it, and under what conditions?
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