linux-kernel - Re: [PATCH 1/5] mm: rmap: fix cache flush on THP pages

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Date:   Mon, 24 Jan 2022 16:51:06 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>, apopple@...dia.com,
        Yang Shi <shy828301@...il.com>, rcampbell@...dia.com,
        Hugh Dickins <hughd@...gle.com>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        zwisler@...nel.org, linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        nvdimm@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH 1/5] mm: rmap: fix cache flush on THP pages

On Mon, Jan 24, 2022 at 3:34 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Fri, Jan 21, 2022 at 03:55:11PM +0800, Muchun Song wrote:
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index b0fd9dc19eba..65670cb805d6 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -974,7 +974,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
> >                       if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
> >                               continue;
> >
> > -                     flush_cache_page(vma, address, page_to_pfn(page));
> > +                     flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
>
> Do we need a flush_cache_folio here given that we must be dealing with
> what effectively is a folio here?

I think it is a future improvement. I suspect it will be easy if
someone wants to backport this patch. If we do not want
someone to do this, I think it is better to introduce
flush_cache_folio in this patch. What do you think?

>
> Also please avoid the overly long line.
>

OK.

Thanks.