linux-kernel - Re: [PATCHv3 13/41] truncate: make sure invalidate_mapping

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Message-ID: <20161011155815.GM6952@quack2.suse.cz>
Date:   Tue, 11 Oct 2016 17:58:15 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-block@...r.kernel.org
Subject: Re: [PATCHv3 13/41] truncate: make sure invalidate_mapping_pages()
 can discard huge pages

On Thu 15-09-16 14:54:55, Kirill A. Shutemov wrote:
> invalidate_inode_page() has expectation about page_count() of the page
> -- if it's not 2 (one to caller, one to radix-tree), it will not be
> dropped. That condition almost never met for THPs -- tail pages are
> pinned to the pagevec.
> 
> Let's drop them, before calling invalidate_inode_page().
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  mm/truncate.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/mm/truncate.c b/mm/truncate.c
> index a01cce450a26..ce904e4b1708 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -504,10 +504,21 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
>  				/* 'end' is in the middle of THP */
>  				if (index ==  round_down(end, HPAGE_PMD_NR))
>  					continue;
> +				/*
> +				 * invalidate_inode_page() expects
> +				 * page_count(page) == 2 to drop page from page
> +				 * cache -- drop tail pages references.
> +				 */
> +				get_page(page);
> +				pagevec_release(&pvec);

I'm not quite sure why this is needed. When you have multiorder entry in
the radix tree for your huge page, then you should not get more entries in
the pagevec for your huge page. What do I miss?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR