On 06/21/2016 12:27 AM, David Rientjes wrote:
If the memory compaction free scanner cannot successfully split a free
page (only possible due to per-zone low watermark), terminate the free
scanner rather than continuing to scan memory needlessly.
If the per-zone watermark is insufficient for a free page of
order <= cc->order, then terminate the scanner since future splits will
also likely fail.
This prevents the compaction freeing scanner from scanning all memory on
very large zones (very noticeable for zones > 128GB, for instance) when
all splits will likely fail.
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
But some notes below.
---
mm/compaction.c | 49 +++++++++++++++++++++++++++++--------------------
1 file changed, 29 insertions(+), 20 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -494,24 +494,22 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
/* Found a free page, will break it into order-0 pages */
order = page_order(page);
- isolated = __isolate_free_page(page, page_order(page));
+ isolated = __isolate_free_page(page, order);
+ if (!isolated)
+ break;
This seems to fix as a side-effect a bug in Joonsoo's mmotm patch
mm-compaction-split-freepages-without-holding-the-zone-lock.patch, that
Minchan found: http://marc.info/?l=linux-mm&m=146607176528495&w=2
So it should be noted somewhere so they are merged together. Or Joonsoo
posts an isolated fix and this patch has to rebase.
set_page_private(page, order);
total_isolated += isolated;
list_add_tail(&page->lru, freelist);
- /* If a page was split, advance to the end of it */
- if (isolated) {
- cc->nr_freepages += isolated;
- if (!strict &&
- cc->nr_migratepages <= cc->nr_freepages) {
- blockpfn += isolated;
- break;
- }
-
- blockpfn += isolated - 1;
- cursor += isolated - 1;
- continue;
+ /* Advance to the end of split page */
+ cc->nr_freepages += isolated;
+ if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
+ blockpfn += isolated;
+ break;
}
+ blockpfn += isolated - 1;
+ cursor += isolated - 1;
+ continue;
isolate_fail:
if (strict)
@@ -521,6 +519,9 @@ isolate_fail:
}
+ if (locked)
+ spin_unlock_irqrestore(&cc->zone->lock, flags);
+
/*
* There is a tiny chance that we have read bogus compound_order(),
* so be careful to not go outside of the pageblock.
@@ -542,9 +543,6 @@ isolate_fail:
if (strict && blockpfn < end_pfn)
total_isolated = 0;
- if (locked)
- spin_unlock_irqrestore(&cc->zone->lock, flags);
-
/* Update the pageblock-skip if the whole pageblock was scanned */
if (blockpfn == end_pfn)
update_pageblock_skip(cc, valid_page, total_isolated, false);
@@ -622,7 +620,7 @@ isolate_freepages_range(struct compact_control *cc,
*/
}
- /* split_free_page does not map the pages */
+ /* __isolate_free_page() does not map the pages */
map_pages(&freelist);
if (pfn < end_pfn) {
@@ -1071,6 +1069,7 @@ static void isolate_freepages(struct compact_control *cc)
block_end_pfn = block_start_pfn,
block_start_pfn -= pageblock_nr_pages,
isolate_start_pfn = block_start_pfn) {
+ unsigned long isolated;
/*
* This can iterate a massively long zone without finding any
@@ -1095,8 +1094,12 @@ static void isolate_freepages(struct compact_control *cc)
continue;
/* Found a block suitable for isolating free pages from. */
- isolate_freepages_block(cc, &isolate_start_pfn,
- block_end_pfn, freelist, false);
+ isolated = isolate_freepages_block(cc, &isolate_start_pfn,
+ block_end_pfn, freelist, false);
+ /* If free page split failed, do not continue needlessly */
More accurately, free page isolation failed?
+ if (!isolated && isolate_start_pfn < block_end_pfn &&
+ cc->nr_freepages <= cc->nr_migratepages)
+ break;
/*
* If we isolated enough freepages, or aborted due to async
@@ -1124,7 +1127,7 @@ static void isolate_freepages(struct compact_control *cc)
}
}
- /* split_free_page does not map the pages */
+ /* __isolate_free_page() does not map the pages */
map_pages(freelist);
/*
@@ -1703,6 +1706,12 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
continue;
}
+ /* Don't attempt compaction if splitting free page will fail */
+ if (!zone_watermark_ok(zone, 0,
+ low_wmark_pages(zone) + (1 << order),
+ 0, 0))
+ continue;
+
Please don't add this, compact_zone already checks this via
compaction_suitable() (and the usual 2 << order gap), so this is adding
yet another watermark check with a different kind of gap.
Thanks.
status = compact_zone_order(zone, order, gfp_mask, mode,
&zone_contended, alloc_flags,
ac_classzone_idx(ac));
--
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