> On Wed, 05 Sep 2007 19:01:25 -0400 Rik van Riel <[EMAIL PROTECTED]> wrote: > 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!
crap. I guess suitably-fashioned mlock could do the same thing. > 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. hm. Did highmem's all_unreclaimable get set? If so perhaps we could use that in some way. > 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-excessive-pageout.patch text/x-patch (715B)] > --- 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. > + */ > + if (!zone_watermark_ok(zone, order, 8*zone->pages_high, > + end_zone, 0)) > + nr_reclaimed += shrink_zone(priority, zone, > &sc); > reclaim_state->reclaimed_slab = 0; > nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL, > lru_pages); I guess for a very small upper zone and a very large lower zone this could still put the scan balancing out of whack, fixable by a smarter version of "8*zone->pages_high" but it doesn't seem very likely that this will affect things much. Why doesn't direct reclaim need similar treatment? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
