On 21 Aug 2023, at 14:33, Johannes Weiner wrote:
> The buddy allocator coalesces compatible blocks during freeing, but it
> doesn't update the types of the subblocks to match. When an allocation
> later breaks the chunk down again, its pieces will be put on freelists
> of the wrong type. This encourages incompatible page mixing (ask for
> one type, get another), and thus long-term fragmentation.
>
> Update the subblocks when merging a larger chunk, such that a later
> expand() will maintain freelist type hygiene.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> mm/page_alloc.c | 37 ++++++++++++++++++++++---------------
> 1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a5e36d186893..6c9f565b2613 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -438,6 +438,17 @@ void set_pageblock_migratetype(struct page *page, int migratetype)
> page_to_pfn(page), MIGRATETYPE_MASK);
> }
>
> +static void change_pageblock_range(struct page *pageblock_page,
> + int start_order, int migratetype)
> +{
> + int nr_pageblocks = 1 << (start_order - pageblock_order);
> +
> + while (nr_pageblocks--) {
> + set_pageblock_migratetype(pageblock_page, migratetype);
> + pageblock_page += pageblock_nr_pages;
> + }
> +}
> +
Is this code move included by accident?
> #ifdef CONFIG_DEBUG_VM
> static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
> {
> @@ -808,10 +819,17 @@ static inline void __free_one_page(struct page *page,
> */
> int buddy_mt = get_pfnblock_migratetype(buddy, buddy_pfn);
>
> - if (migratetype != buddy_mt
> - && (!migratetype_is_mergeable(migratetype) ||
> - !migratetype_is_mergeable(buddy_mt)))
> - goto done_merging;
> + if (migratetype != buddy_mt) {
> + if (!migratetype_is_mergeable(migratetype) ||
> + !migratetype_is_mergeable(buddy_mt))
> + goto done_merging;
> + /*
> + * Match buddy type. This ensures that
> + * an expand() down the line puts the
> + * sub-blocks on the right freelists.
> + */
> + set_pageblock_migratetype(buddy, migratetype);
> + }
> }
>
> /*
> @@ -1687,17 +1705,6 @@ int move_freepages_block(struct zone *zone, struct page *page,
> num_movable);
> }
>
> -static void change_pageblock_range(struct page *pageblock_page,
> - int start_order, int migratetype)
> -{
> - int nr_pageblocks = 1 << (start_order - pageblock_order);
> -
> - while (nr_pageblocks--) {
> - set_pageblock_migratetype(pageblock_page, migratetype);
> - pageblock_page += pageblock_nr_pages;
> - }
> -}
> -
> /*
> * When we are falling back to another migratetype during allocation, try to
> * steal extra free pages from the same pageblocks to satisfy further
> --
> 2.41.0
--
Best Regards,
Yan, Zi
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