Re: [PATCH v4 3/3] mm/compaction: optimize >0 order folio compaction with free page split.

From: Yu Zhao
Date: Mon Feb 12 2024 - 13:28:27 EST


On Mon, Feb 12, 2024 at 9:35 AM Zi Yan <zi.yan@xxxxxxxx> wrote:
>
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> During migration in a memory compaction, free pages are placed in an array
> of page lists based on their order. But the desired free page order
> (i.e., the order of a source page) might not be always present, thus
> leading to migration failures and premature compaction termination. Split
> a high order free pages when source migration page has a lower order to
> increase migration successful rate.
>
> Note: merging free pages when a migration fails and a lower order free
> page is returned via compaction_free() is possible, but there is too much
> work. Since the free pages are not buddy pages, it is hard to identify
> these free pages using existing PFN-based page merging algorithm.
>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: Adam Manzanares <a.manzanares@xxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
> Cc: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
> ---
> mm/compaction.c | 36 +++++++++++++++++++++++++++++++-----
> 1 file changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index d0a05a621b67..25908e36b97c 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1832,15 +1832,41 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
> struct compact_control *cc = (struct compact_control *)data;
> struct folio *dst;
> int order = folio_order(src);
> + bool has_isolated_pages = false;
> + int start_order;
> + struct page *freepage;
> + unsigned long size;
> +
> +again:
> + for (start_order = order; start_order < NR_PAGE_ORDERS; start_order++)
> + if (!list_empty(&cc->freepages[start_order]))
> + break;
>
> - if (list_empty(&cc->freepages[order])) {
> - isolate_freepages(cc);
> - if (list_empty(&cc->freepages[order]))
> + /* no free pages in the list */
> + if (start_order == NR_PAGE_ORDERS) {
> + if (!has_isolated_pages) {
> + isolate_freepages(cc);
> + has_isolated_pages = true;
> + goto again;
> + } else
> return NULL;

Nit: remove the "else" above, or just:

if (has_isolated_pages)
return NULL;
isolate_freepages(cc);
has_isolated_pages = true;
goto again;