Re: [PATCH v5 10/12] mm/page_alloc: retry alloc_contig_pages() when the zonelist is rebuilt

["Zi Yan" <ziy@nvidia.com>]

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: stable@vger.kernel.org
> Signed-off-by: Gregory Price (Meta) <gourry@gourry.net >
> Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> ---
>  mm/page_alloc.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>

LGTM.

Acked-by: Zi Yan <ziy@nvidia.com>

-- 
Best Regards,
Yan, Zi