linux-kernel - Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache

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Date:   Tue, 28 Sep 2021 09:59:49 -0700
From:   Song Liu <song@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Rongwei Wang <rongwei.wang@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        William Kucharski <william.kucharski@...cle.com>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache

On Tue, Sep 28, 2021 at 5:07 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Mon, Sep 27, 2021 at 03:24:47PM -0700, Song Liu wrote:
> > OTOH, does it make sense to block writes within khugepaged, like:
> > @@ -1652,6 +1653,11 @@ static void collapse_file(struct mm_struct *mm,
> >         /* Only allocate from the target node */
> >         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
> >
> > +       if (deny_write_access(file)) {
> > +               result = SCAN_BUSY_WRITE;
> > +               return;
> > +       }
>
> The problem is that it denies, rather than blocking.  That means that the
> writer gets ETXTBSY instead of waiting until khugepaged is done.
>

Yes, I was thinking about the same problem last night and this morning.
Unfortunately, I haven't got a good solution yet. Do you have some
suggestions on this?

Thanks,
Song