On 21 Feb 2020, at 16:53, Rik van Riel wrote:
> 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@xxxxxxxxxxx>
> ---
> mm/compaction.c | 16 +++++++++-------
> mm/page_alloc.c | 6 ++++--
> 2 files changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 672d3c78c6ab..f3e05c91df62 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -894,12 +894,12 @@ 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 most of the time. 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.
> */
Maybe add “we do want to move them when allocating contiguous memory using CMA” to help
people understand the context of using cc->alloc_contig?
> - if (PageCompound(page)) {
> + if (PageCompound(page) && !cc->alloc_contig) {
> const unsigned int order = compound_order(page);
>
> if (likely(order < MAX_ORDER))
> @@ -969,7 +969,7 @@ 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;
> }
> @@ -981,7 +981,9 @@ 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));
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a36736812596..38c8ddfcecc8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8253,14 +8253,16 @@ 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 (PageTransHuge(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;
>
> skip_pages = compound_nr(head) - (page - head);
> --
> 2.24.1
Everything else looks good to me.
Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
--
Best Regards,
Yan Zi
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