linux-kernel - Re: [PATCH v2 4/5] mm/thp: allow drop THP from page cache

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Date:   Fri, 18 Oct 2019 16:32:31 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Yang Shi <shy828301@...il.com>
Cc:     Song Liu <songliubraving@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        matthew.wilcox@...cle.com, kernel-team@...com,
        william.kucharski@...cle.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v2 4/5] mm/thp: allow drop THP from page cache

On Thu, Oct 17, 2019 at 02:46:38PM -0700, Yang Shi wrote:
> On Thu, Oct 17, 2019 at 9:42 AM Song Liu <songliubraving@...com> wrote:
> >
> > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> >
> > Once a THP is added to the page cache, it cannot be dropped via
> > /proc/sys/vm/drop_caches. Fix this issue with proper handling in
> > invalidate_mapping_pages().
> >
> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Tested-by: Song Liu <songliubraving@...com>
> > Signed-off-by: Song Liu <songliubraving@...com>
> > ---
> >  mm/truncate.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/mm/truncate.c b/mm/truncate.c
> > index 8563339041f6..dd9ebc1da356 100644
> > --- a/mm/truncate.c
> > +++ b/mm/truncate.c
> > @@ -592,6 +592,16 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
> >                                         unlock_page(page);
> >                                         continue;
> >                                 }
> > +
> > +                               /* Take a pin outside pagevec */
> > +                               get_page(page);
> > +
> > +                               /*
> > +                                * Drop extra pins before trying to invalidate
> > +                                * the huge page.
> > +                                */
> > +                               pagevec_remove_exceptionals(&pvec);
> > +                               pagevec_release(&pvec);
> 
> Shall we skip the outer pagevec_remove_exceptions() if it has been done here?

It will be NOP and skipping would complicate the code.

-- 
 Kirill A. Shutemov