linux-kernel - Re: [PATCH v4 1/6] userfaultfd: convert mfill_atomic_pte

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Message-ID: <20230406212848.GA28429@monkey>
Date:   Thu, 6 Apr 2023 14:28:48 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Peng Zhang <zhangpeng362@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        vishal.moola@...il.com, muchun.song@...ux.dev,
        wangkefeng.wang@...wei.com, sunnanyong@...wei.com
Subject: Re: [PATCH v4 1/6] userfaultfd: convert mfill_atomic_pte_copy() to
 use a folio

On 03/30/23 19:02, Matthew Wilcox wrote:
> On Thu, Mar 30, 2023 at 10:02:52AM -0700, Sidhartha Kumar wrote:
> > On 3/30/23 6:40 AM, Peng Zhang wrote:
> > > From: ZhangPeng <zhangpeng362@...wei.com>
> > > 
> > > Call vma_alloc_folio() directly instead of alloc_page_vma(). Add an
> > > assertion that this is a single-page folio and removes several calls to
> > > compound_head().
> 
> There's no added assertion in this patch any more, so I'd drop that
> part of the description.
> 

I thought it was this.

>  
> -		flush_dcache_page(page);
> +		flush_dcache_folio(folio);
>  	} else {
> -		page = *pagep;
> +		folio = page_folio(*pagep);
> +		VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
>  		*pagep = NULL;
>  	}

I was wondering what that VM_BUG_ON_FOLIO was added?
-- 
Mike Kravetz