On Tue, Jul 12, 2016 at 10:29:09AM -0400, Johannes Weiner wrote: > > + /* > > + * If the number of buffer_heads in the machine exceeds the > > + * maximum allowed level then reclaim from all zones. This is > > + * not specific to highmem as highmem may not exist but it is > > + * it is expected that buffer_heads are stripped in writeback. > > The mention of highmem in this comment make only sense within the > context of this diff; it'll be pretty confusing in the standalone > code. > > Also, double "it is" :)
Is this any better? Note that it's marked as a fix to a later patch to reduce collisions in mmotm. It's not a bisection risk so I saw little need to cause unnecessary conflicts for Andrew. ---8<--- mm, vmscan: Have kswapd reclaim from all zones if reclaiming and buffer_heads_over_limit -fix 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]> 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 + * go ahead if all eligible zones for the original allocation + * request are balanced to avoid excessive reclaim from kswapd. */ if (buffer_heads_over_limit) { for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
