linux-kernel - Re: [PATCH v5 5/5] mm: rmap: support batched unmapping for file large folios

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Message-ID: <46d0b6bf-db7e-418f-a497-983db4d4d786@kernel.org>
Date: Mon, 9 Feb 2026 10:38:02 +0100
From: "David Hildenbrand (Arm)" <david@...nel.org>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 catalin.marinas@....com, will@...nel.org
Cc: lorenzo.stoakes@...cle.com, ryan.roberts@....com,
 Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com,
 mhocko@...e.com, riel@...riel.com, harry.yoo@...cle.com, jannh@...gle.com,
 willy@...radead.org, baohua@...nel.org, dev.jain@....com,
 linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/5] mm: rmap: support batched unmapping for file large
 folios

On 12/26/25 07:07, Baolin Wang wrote:
> Similar to folio_referenced_one(), we can apply batched unmapping for file
> large folios to optimize the performance of file folios reclamation.
> 
> Barry previously implemented batched unmapping for lazyfree anonymous large
> folios[1] and did not further optimize anonymous large folios or file-backed
> large folios at that stage. As for file-backed large folios, the batched
> unmapping support is relatively straightforward, as we only need to clear
> the consecutive (present) PTE entries for file-backed large folios.
> 
> Performance testing:
> Allocate 10G clean file-backed folios by mmap() in a memory cgroup, and try to
> reclaim 8G file-backed folios via the memory.reclaim interface. I can observe
> 75% performance improvement on my Arm64 32-core server (and 50%+ improvement
> on my X86 machine) with this patch.
> 
> W/o patch:
> real    0m1.018s
> user    0m0.000s
> sys     0m1.018s
> 
> W/ patch:
> real	0m0.249s
> user	0m0.000s
> sys	0m0.249s
> 
> [1] https://lore.kernel.org/all/20250214093015.51024-4-21cnbao@gmail.com/T/#u
> Reviewed-by: Ryan Roberts <ryan.roberts@....com>
> Acked-by: Barry Song <baohua@...nel.org>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>   mm/rmap.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 985ab0b085ba..e1d16003c514 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1863,9 +1863,10 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio,
>   	end_addr = pmd_addr_end(addr, vma->vm_end);
>   	max_nr = (end_addr - addr) >> PAGE_SHIFT;
>   
> -	/* We only support lazyfree batching for now ... */
> -	if (!folio_test_anon(folio) || folio_test_swapbacked(folio))
> +	/* We only support lazyfree or file folios batching for now ... */
> +	if (folio_test_anon(folio) && folio_test_swapbacked(folio))
>   		return 1;

Right, the anon folio handling would require a bit more work in the


	} else if (folio_test_anon(folio)) {

branch.

Do you intend to tackle that one as well?


I'll reply to the fixup.

-- 
Cheers,

David