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

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Message-ID: <CAGsJ_4yACo0YVmQG4i1cr_w2unEt+SnpbFPg=O79g-2Asho1dA@mail.gmail.com>
Date: Fri, 16 Jan 2026 23:23:09 +0800
From: Barry Song <21cnbao@...il.com>
To: Dev Jain <dev.jain@....com>
Cc: Wei Yang <richard.weiyang@...il.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	akpm@...ux-foundation.org, david@...nel.org, catalin.marinas@....com, 
	will@...nel.org, 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, 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

>
> Thanks for catching this, Dev. I already filter out some of the more
> complex cases, for example:
> if (pte_unused(pte))
>         return 1;
>
> Since the userfaultfd write-protection case is also a corner case,
> could we filter it out as well?
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index c86f1135222b..6bb8ba6f046e 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1870,6 +1870,9 @@ static inline unsigned int
> folio_unmap_pte_batch(struct folio *folio,
>         if (pte_unused(pte))
>                 return 1;
>
> +       if (userfaultfd_wp(vma))
> +               return 1;
> +
>         return folio_pte_batch(folio, pvmw->pte, pte, max_nr);
> }
>
> Just offering a second option — yours is probably better.

Sorry for replying in the wrong place. The above reply was actually meant
for your fix-patch below[1]:

"mm: Fix uffd-wp bit loss when batching file folio unmapping"

[1] https://lore.kernel.org/linux-mm/20260116082721.275178-1-dev.jain@arm.com/

Thanks
Barry