linux-kernel - Re: [PATCH v5 1/8] mm/huge_memory: only split PMD mapping when necessary in unmap

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Message-ID: <99334898-0f5d-4ba1-af38-a510fae473a5@redhat.com>
Date: Wed, 28 Feb 2024 11:30:40 +0100
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>, "Pankaj Raghav (Samsung)"
 <kernel@...kajraghav.com>, linux-mm@...ck.org
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Yang Shi <shy828301@...il.com>, Yu Zhao <yuzhao@...gle.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Ryan Roberts <ryan.roberts@....com>, Michal Koutný
 <mkoutny@...e.com>, Roman Gushchin <roman.gushchin@...ux.dev>,
 Zach O'Keefe <zokeefe@...gle.com>, Hugh Dickins <hughd@...gle.com>,
 Luis Chamberlain <mcgrof@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 1/8] mm/huge_memory: only split PMD mapping when
 necessary in unmap_folio()

On 26.02.24 21:55, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> As multi-size THP support is added, not all THPs are PMD-mapped, thus
> during a huge page split, there is no need to always split PMD mapping
> in unmap_folio(). Make it conditional.
> 
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
>   mm/huge_memory.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 28341a5067fb..b20e535e874c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2727,11 +2727,14 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
>   
>   static void unmap_folio(struct folio *folio)
>   {
> -	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD |
> -		TTU_SYNC | TTU_BATCH_FLUSH;
> +	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC |
> +		TTU_BATCH_FLUSH;
>   
>   	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>   
> +	if (folio_test_pmd_mappable(folio))
> +		ttu_flags |= TTU_SPLIT_HUGE_PMD;
> +
>   	/*
>   	 * Anon pages need migration entries to preserve them, but file
>   	 * pages can simply be left unmapped, then faulted back on demand.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb