Re: [PATCH v4] page cache: Store only head pages in i_pages

From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Hugh Dickins <hughd@google.com>,
	Jan Kara <jack@suse.cz>, Song Liu <liu.song.a23@gmail.com>
Subject: Re: [PATCH v4] page cache: Store only head pages in i_pages
Date: Wed, 12 Jun 2019 04:46:34 +0300	[thread overview]
Message-ID: <20190612014634.f23fjumw666jj52s@box> (raw)
In-Reply-To: <155951205528.18214.706102020945306720@skylake-alporthouse-com>

On Sun, Jun 02, 2019 at 10:47:35PM +0100, Chris Wilson wrote:
> Quoting Matthew Wilcox (2019-03-07 15:30:51)
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 404acdcd0455..aaf88f85d492 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -2456,6 +2456,9 @@ static void __split_huge_page(struct page *page, struct list_head *list,
> >                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
> >                                 shmem_uncharge(head->mapping->host, 1);
> >                         put_page(head + i);
> > +               } else if (!PageAnon(page)) {
> > +                       __xa_store(&head->mapping->i_pages, head[i].index,
> > +                                       head + i, 0);
> 
> Forgiving the ignorant copy'n'paste, this is required:
> 
> +               } else if (PageSwapCache(page)) {
> +                       swp_entry_t entry = { .val = page_private(head + i) };
> +                       __xa_store(&swap_address_space(entry)->i_pages,
> +                                  swp_offset(entry),
> +                                  head + i, 0);
>                 }
>         }
>  
> The locking is definitely wrong.

Does it help with the problem, or it's just a possible lead?

-- 
 Kirill A. Shutemov