On Sat Oct 31, 2026 at 10:13 PM EDT, Gregory Price (Meta) wrote:
> Onlining the first block of a zone rebuilds every zonelist in place,
> shifting the slots after the new zone.
> alloc_contig_frozen_pages_noprof() approves a slot by the caller's gfp
> and nodemask, then loads the zone from it:
>
> CPU 0 CPU 1
> alloc_contig_frozen_pages_noprof(GFP_HIGHUSER | __GFP_THISNODE)
> slot 0 (NORMAL1) approved
> online_pages()
> build_all_zonelists()
> [NORMAL1]
> -> [MOVABLE1, NORMAL1]
> zone = zonelist_zone(slot 0) /* MOVABLE1 */
> alloc_contig_frozen_range(MOVABLE1 pfns)
>
> A gigantic hugetlb page can then land in ZONE_MOVABLE, and a nodemask
> caller can get a range from another node. Gigantic pages are kept out
> of ZONE_MOVABLE since commit 79b63f12abcb ("mm, hugetlb: do not allocate
> non-migrateable gigantic pages from movable zones").
>
> Check zonelist_update_seq before using each zone, and restart the walk
> if it changed, as the hugetlb pool walk does. Check again before
> escalating to the pass that may migrate hugetlb pages, so a pass a
> rebuild cut short is redone rather than escalated.
>
> With kprobes holding the walk across the online, the base kernel put the
> 1G page in ZONE_MOVABLE in 3 of 3 runs, and this change put it in
> ZONE_NORMAL in 3 of 3. Direct GFP_KERNEL calls with nodemask {1} and
> {2} got a ZONE_MOVABLE range and a node 1 range on base, 3 of 3 each,
> and neither with this change.
>
> Fixes: 5e27a2df03b8 ("mm/page_alloc: add alloc_contig_pages()")
> Cc: [email protected]
> Signed-off-by: Gregory Price (Meta) <[email protected] >
> Reviewed-by: Vlastimil Babka (SUSE) <[email protected]>
> ---
> mm/page_alloc.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
LGTM.
Acked-by: Zi Yan <[email protected]>
--
Best Regards,
Yan, Zi
