Re: [PATCH v1 1/2] mm/page_alloc: conditionally split > pageblock_order pages in free_one_page() and move_freepages_block_isolate()

[Yu Zhao <yuzhao@google.com>]

On Fri, Dec 6, 2024 at 3:00 AM David Hildenbrand <david@redhat.com> wrote:
>
> Let's special-case for the common scenarios that:
>
> (a) We are freeing pages <= pageblock_order
> (b) We are freeing a page <= MAX_PAGE_ORDER and all pageblocks match
>     (especially, no mixture of isolated and non-isolated pageblocks)
>
> When we encounter a > MAX_PAGE_ORDER page, it can only come from
> alloc_contig_range(), and we can process MAX_PAGE_ORDER chunks.
>
> When we encounter a >pageblock_order <= MAX_PAGE_ORDER page,
> check whether all pageblocks match, and if so (common case), don't
> split them up just for the buddy to merge them back.
>
> This makes sure that when we free MAX_PAGE_ORDER chunks to the buddy,
> for example during system startups, memory onlining, or when isolating
> consecutive pageblocks via alloc_contig_range()/memory offlining, that
> we don't unnecessarily split up what we'll immediately merge again,
> because the migratetypes match.
>
> Rename split_large_buddy() to __free_one_page_maybe_split(), to make it
> clearer what's happening, and handle in it only natural buddy orders,
> not the alloc_contig_range(__GFP_COMP) special case: handle that in
> free_one_page() only.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Yu Zhao <yuzhao@google.com>