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Date: Wed, 10 Dec 2014 15:38:40 +0900
From: Joonsoo Kim <iamjoonsoo.kim@....com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mgorman@...e.de>,
David Rientjes <rientjes@...gle.com>,
Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mm/page_alloc: expands broken freepage to proper
buddy list when steal
On Mon, Dec 08, 2014 at 10:29:44AM +0100, Vlastimil Babka wrote:
> On 12/08/2014 08:16 AM, Joonsoo Kim wrote:
> >There is odd behaviour when we steal freepages from other migratetype
> >buddy list. In try_to_steal_freepages(), we move all freepages in
> >the pageblock that founded freepage is belong to to the request
> >migratetype in order to mitigate fragmentation. If the number of moved
> >pages are enough to change pageblock migratetype, there is no problem. If
> >not enough, we don't change pageblock migratetype and add broken freepages
> >to the original migratetype buddy list rather than request migratetype
> >one. For me, this is odd, because we already moved all freepages in this
> >pageblock to the request migratetype. This patch fixes this situation to
> >add broken freepages to the request migratetype buddy list in this case.
>
> I'd rather split the fix from the refactoring. And maybe my
> description is longer, but easier to understand? (I guess somebody
> else should judge this)
Your patch is much better to understand than mine. :)
No need to judge from somebody else.
After your patch is merged, I will resubmit these on top of it.
>
> >This patch introduce new function that can help to decide if we can
> >steal the page without resulting in fragmentation. It will be used in
> >following patch for compaction finish criteria.
> >
> >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> >---
> > include/trace/events/kmem.h | 7 +++--
> > mm/page_alloc.c | 72 +++++++++++++++++++++++++------------------
> > 2 files changed, 46 insertions(+), 33 deletions(-)
> >
> >diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> >index aece134..4ad10ba 100644
> >--- a/include/trace/events/kmem.h
> >+++ b/include/trace/events/kmem.h
> >@@ -268,11 +268,11 @@ TRACE_EVENT(mm_page_alloc_extfrag,
> >
> > TP_PROTO(struct page *page,
> > int alloc_order, int fallback_order,
> >- int alloc_migratetype, int fallback_migratetype, int new_migratetype),
> >+ int alloc_migratetype, int fallback_migratetype),
> >
> > TP_ARGS(page,
> > alloc_order, fallback_order,
> >- alloc_migratetype, fallback_migratetype, new_migratetype),
> >+ alloc_migratetype, fallback_migratetype),
> >
> > TP_STRUCT__entry(
> > __field( struct page *, page )
> >@@ -289,7 +289,8 @@ TRACE_EVENT(mm_page_alloc_extfrag,
> > __entry->fallback_order = fallback_order;
> > __entry->alloc_migratetype = alloc_migratetype;
> > __entry->fallback_migratetype = fallback_migratetype;
> >- __entry->change_ownership = (new_migratetype == alloc_migratetype);
> >+ __entry->change_ownership = (alloc_migratetype ==
> >+ get_pageblock_migratetype(page));
> > ),
> >
> > TP_printk("page=%p pfn=%lu alloc_order=%d fallback_order=%d pageblock_order=%d alloc_migratetype=%d fallback_migratetype=%d fragmenting=%d change_ownership=%d",
> >diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >index 7c46d0f..7b4c9aa 100644
> >--- a/mm/page_alloc.c
> >+++ b/mm/page_alloc.c
> >@@ -1139,44 +1139,50 @@ static void change_pageblock_range(struct page *pageblock_page,
> > * Returns the new migratetype of the pageblock (or the same old migratetype
> > * if it was unchanged).
> > */
> >-static int try_to_steal_freepages(struct zone *zone, struct page *page,
> >- int start_type, int fallback_type)
> >+static void try_to_steal_freepages(struct zone *zone, struct page *page,
> >+ int target_mt)
> > {
> >+ int pages;
> > int current_order = page_order(page);
> >
> >- /*
> >- * When borrowing from MIGRATE_CMA, we need to release the excess
> >- * buddy pages to CMA itself. We also ensure the freepage_migratetype
> >- * is set to CMA so it is returned to the correct freelist in case
> >- * the page ends up being not actually allocated from the pcp lists.
> >- */
> >- if (is_migrate_cma(fallback_type))
> >- return fallback_type;
> >-
> > /* Take ownership for orders >= pageblock_order */
> > if (current_order >= pageblock_order) {
> >- change_pageblock_range(page, current_order, start_type);
> >- return start_type;
> >+ change_pageblock_range(page, current_order, target_mt);
> >+ return;
>
> So here's a (current_order >= pageblock_order) check.
>
> > }
> >
> >- if (current_order >= pageblock_order / 2 ||
> >- start_type == MIGRATE_RECLAIMABLE ||
> >- page_group_by_mobility_disabled) {
> >- int pages;
> >+ pages = move_freepages_block(zone, page, target_mt);
> >
> >- pages = move_freepages_block(zone, page, start_type);
> >+ /* Claim the whole block if over half of it is free */
> >+ if (pages >= (1 << (pageblock_order-1)) ||
> >+ page_group_by_mobility_disabled) {
> >
> >- /* Claim the whole block if over half of it is free */
> >- if (pages >= (1 << (pageblock_order-1)) ||
> >- page_group_by_mobility_disabled) {
> >+ set_pageblock_migratetype(page, target_mt);
> >+ }
> >+}
> >
> >- set_pageblock_migratetype(page, start_type);
> >- return start_type;
> >- }
> >+static bool can_steal_freepages(unsigned int order,
> >+ int start_mt, int fallback_mt)
> >+{
> >+ /*
> >+ * When borrowing from MIGRATE_CMA, we need to release the excess
> >+ * buddy pages to CMA itself. We also ensure the freepage_migratetype
> >+ * is set to CMA so it is returned to the correct freelist in case
> >+ * the page ends up being not actually allocated from the pcp lists.
> >+ */
> >+ if (is_migrate_cma(fallback_mt))
> >+ return false;
> >
> >- }
> >+ /* Can take ownership for orders >= pageblock_order */
> >+ if (order >= pageblock_order)
> >+ return true;
>
> And another check.
>
> >+
> >+ if (order >= pageblock_order / 2 ||
> >+ start_mt == MIGRATE_RECLAIMABLE ||
> >+ page_group_by_mobility_disabled)
> >+ return true;
> >
> >- return fallback_type;
> >+ return false;
> > }
> >
> > /* Remove an element from the buddy allocator from the fallback list */
> >@@ -1187,6 +1193,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
> > unsigned int current_order;
> > struct page *page;
> > int migratetype, new_type, i;
> >+ bool can_steal;
> >
> > /* Find the largest possible block of pages in the other list */
> > for (current_order = MAX_ORDER-1;
> >@@ -1194,6 +1201,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
> > --current_order) {
> > for (i = 0;; i++) {
> > migratetype = fallbacks[start_migratetype][i];
> >+ new_type = migratetype;
> >
> > /* MIGRATE_RESERVE handled later if necessary */
> > if (migratetype == MIGRATE_RESERVE)
> >@@ -1207,9 +1215,13 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
> > struct page, lru);
> > area->nr_free--;
>
> So wouldn't it be better to handle the "order >= pageblock_order"
> case separately at this level? I think it would be better also for
> the compaction case (I'll comment on the later patch why).
I will also comment on the later patch.
Thanks.
>
> >- new_type = try_to_steal_freepages(zone, page,
> >- start_migratetype,
> >- migratetype);
> >+ can_steal = can_steal_freepages(current_order,
> >+ start_migratetype, migratetype);
> >+ if (can_steal) {
> >+ new_type = start_migratetype;
> >+ try_to_steal_freepages(zone, page,
> >+ start_migratetype);
> >+ }
> >
> > /* Remove the page from the freelists */
> > list_del(&page->lru);
> >@@ -1225,7 +1237,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
> > set_freepage_migratetype(page, new_type);
> >
> > trace_mm_page_alloc_extfrag(page, order, current_order,
> >- start_migratetype, migratetype, new_type);
> >+ start_migratetype, migratetype);
> >
> > return page;
> > }
> >
>
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