[v2,0/2] mm/page_alloc: rework conditional splitting >= pageblock_order pages when freeing

Message

David Hildenbrand Dec. 10, 2024, 10:29 a.m. UTC

Now based on [1].

Looking into recent alloc_contig_range(__GFP_COMP) support, I realized that
we now unconditionally split up high-order pages on the page freeing path
to free in pageblock granularity, just to immediately let the buddy merge
them again in the common case.

Let's optimize for the common case (all pageblock migratetypes match), and
enable it only in configs where this is strictly required. Further, add
some comments that explain why this special casing is required at all.

Alongside, a fix for a stale comment in page isolation code.

Tested with runtime allocation of gigantic pages and virtio-mem.

v1 -> v2:
* "mm/page_alloc: conditionally split > pageblock_order pages in
   free_one_page() and move_freepages_block_isolate()"
 -> Similarly avoid pfn_to_page() on something that might not be a valid pfn
 -> Add a comment regarding using "zone->nr_isolate_pageblock" in the
    future to the patch description

Cc: Andrew Morton <[e-mail]>
Cc: Zi Yan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Yu Zhao <[e-mail]>

[1] https://lkml.kernel.org/r/[e-mail]

David Hildenbrand (2):
  mm/page_alloc: conditionally split > pageblock_order pages in
    free_one_page() and move_freepages_block_isolate()
  mm/page_isolation: fixup isolate_single_pageblock() comment regarding
    splitting free pages

 mm/page_alloc.c     | 73 ++++++++++++++++++++++++++++++++++++---------
 mm/page_isolation.c |  9 +++---
 2 files changed, 63 insertions(+), 19 deletions(-)