On Wed, Jul 13, 2016 at 11:00:01AM +0100, Mel Gorman wrote: > Johannes reported that the comment about buffer_heads_over_limit in > balance_pgdat only made sense in the context of the patch. This patch > clarifies the reasoning and how it applies to 32 and 64 bit systems. > > This is a fix to the mmotm patch > mm-vmscan-have-kswapd-reclaim-from-all-zones-if-reclaiming-and-buffer_heads_over_limit.patch > > Suggested-by: Johannes Weiner <[email protected]> > Signed-off-by: Mel Gorman <[email protected]> > --- > mm/vmscan.c | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index d079210d46ee..21eae17ee730 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3131,12 +3131,13 @@ static int balance_pgdat(pg_data_t *pgdat, int order, > int classzone_idx) > > /* > * If the number of buffer_heads exceeds the maximum allowed > - * then consider reclaiming from all zones. This is not > - * specific to highmem which may not exist but it is it is > - * expected that buffer_heads are stripped in writeback. > - * Reclaim may still not go ahead if all eligible zones > - * for the original allocation request are balanced to > - * avoid excessive reclaim from kswapd. > + * then consider reclaiming from all zones. This has a dual > + * purpose -- on 64-bit systems it is expected that > + * buffer_heads are stripped during active rotation. On 32-bit > + * systems, highmem pages can pin lowmem memory and shrinking > + * buffers can relieve lowmem pressure. Reclaim may still not
It's good but I hope we can make it more clear. On 32-bit systems, highmem pages can pin lowmem pages storing buffer_heads so shrinking highmem pages can relieve lowmem pressure. If you don't think it's much readable compared to yours, feel free to drop. Thanks.
