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Subject[PATCH v2 2/2] mm,thp,compaction,cma: allow THP migration for CMA allocations
Date
The code to implement THP migrations already exists, and the code
for CMA to clear out a region of memory already exists.

Only a few small tweaks are needed to allow CMA to move THP memory
when attempting an allocation from alloc_contig_range.

With these changes, migrating THPs from a CMA area works when
allocating a 1GB hugepage from CMA memory.

Signed-off-by: Rik van Riel <riel@surriel.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
---
mm/compaction.c | 22 +++++++++++++---------
mm/page_alloc.c | 9 +++++++--
2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 672d3c78c6ab..000ade085b89 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -894,12 +894,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,

/*
* Regardless of being on LRU, compound pages such as THP and
- * hugetlbfs are not to be compacted. We can potentially save
- * a lot of iterations if we skip them at once. The check is
- * racy, but we can consider only valid values and the only
- * danger is skipping too much.
+ * hugetlbfs are not to be compacted unless we are attempting
+ * an allocation much larger than the huge page size (eg CMA).
+ * We can potentially save a lot of iterations if we skip them
+ * at once. The check is racy, but we can consider only valid
+ * values and the only danger is skipping too much.
*/
- if (PageCompound(page)) {
+ if (PageCompound(page) && !cc->alloc_contig) {
const unsigned int order = compound_order(page);

if (likely(order < MAX_ORDER))
@@ -969,7 +970,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
* and it's on LRU. It can only be a THP so the order
* is safe to read and it's 0 for tail pages.
*/
- if (unlikely(PageCompound(page))) {
+ if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
low_pfn += compound_nr(page) - 1;
goto isolate_fail;
}
@@ -981,12 +982,15 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if (__isolate_lru_page(page, isolate_mode) != 0)
goto isolate_fail;

- VM_BUG_ON_PAGE(PageCompound(page), page);
+ /* The whole page is taken off the LRU; skip the tail pages. */
+ if (PageCompound(page))
+ low_pfn += compound_nr(page) - 1;

/* Successfully isolated */
del_page_from_lru_list(page, lruvec, page_lru(page));
- inc_node_page_state(page,
- NR_ISOLATED_ANON + page_is_file_cache(page));
+ mod_node_page_state(page_pgdat(page),
+ NR_ISOLATED_ANON + page_is_file_cache(page),
+ hpage_nr_pages(page));

isolate_success:
list_add(&page->lru, &cc->migratepages);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a36736812596..6257c849cc00 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8253,14 +8253,19 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,

/*
* Hugepages are not in LRU lists, but they're movable.
+ * THPs are on the LRU, but need to be counted as #small pages.
* We need not scan over tail pages because we don't
* handle each tail page individually in migration.
*/
- if (PageHuge(page)) {
+ if (PageHuge(page) || PageTransCompound(page)) {
struct page *head = compound_head(page);
unsigned int skip_pages;

- if (!hugepage_migration_supported(page_hstate(head)))
+ if (PageHuge(page) &&
+ !hugepage_migration_supported(page_hstate(head)))
+ return page;
+
+ if (!PageLRU(head) && !__PageMovable(head))
return page;

skip_pages = compound_nr(head) - (page - head);
--
2.24.1
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