Re: [PATCH 6.6 05/60] mm: migrate: remove PageTransHuge check in numamigrate_isolate_page()

[Hugh Dickins]

On Wed, 13 Mar 2024, Sasha Levin wrote:

> From: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> 
> [ Upstream commit a8ac4a767dcd9d87d8229045904d9fe15ea5e0e8 ]
> 
> Patch series "mm: migrate: more folio conversion and unification", v3.
> 
> Convert more migrate functions to use a folio, it is also a preparation
> for large folio migration support when balancing numa.
> 
> This patch (of 8):
> 
> The assert VM_BUG_ON_PAGE(order && !PageTransHuge(page), page) is not very
> useful,
> 
>    1) for a tail/base page, order = 0, for a head page, the order > 0 &&
>       PageTransHuge() is true
>    2) there is a PageCompound() check and only base page is handled in
>       do_numa_page(), and do_huge_pmd_numa_page() only handle PMD-mapped
>       THP
>    3) even though the page is a tail page, isolate_lru_page() will post
>       a warning, and fail to isolate the page
>    4) if large folio/pte-mapped THP migration supported in the future,
>       we could migrate the entire folio if numa fault on a tail page
> 
> so just remove the check.
> 
> Link: https://lkml.kernel.org/r/20230913095131.2426871-1-wangkefeng.wang@xxxxxxxxxx
> Link: https://lkml.kernel.org/r/20230913095131.2426871-2-wangkefeng.wang@xxxxxxxxxx
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> Suggested-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Stable-dep-of: 2774f256e7c0 ("mm/vmscan: fix a bug calling wakeup_kswapd() with a wrong zone index")

No it is not: that one is appropriate to include, this one is not.

Hugh

> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  mm/migrate.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index b4d972d80b10c..6f8ad6b64c9bc 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2506,8 +2506,6 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>  	int nr_pages = thp_nr_pages(page);
>  	int order = compound_order(page);
>  
> -	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
> -
>  	/* Do not migrate THP mapped by multiple processes */
>  	if (PageTransHuge(page) && total_mapcount(page) > 1)
>  		return 0;
> -- 
> 2.43.0
> 
>