linux-kernel - Re: [PATCH v2] page cache: Store only head pages in i

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Message-ID: <20190214222944.74ipvbnvo2lvfgnr@kshutemo-mobl1>
Date:   Fri, 15 Feb 2019 01:29:44 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>
Subject: Re: [PATCH v2] page cache: Store only head pages in i_pages

On Thu, Feb 14, 2019 at 04:30:04PM +0300, Kirill A. Shutemov wrote:
> On Tue, Feb 12, 2019 at 10:34:54AM -0800, Matthew Wilcox wrote:
> > Transparent Huge Pages are currently stored in i_pages as pointers to
> > consecutive subpages.  This patch changes that to storing consecutive
> > pointers to the head page in preparation for storing huge pages more
> > efficiently in i_pages.
> > 
> > Large parts of this are "inspired" by Kirill's patch
> > https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/
> > 
> > Signed-off-by: Matthew Wilcox <willy@...radead.org>
> 
> I believe I found few missing pieces:
> 
>  - page_cache_delete_batch() will blow up on
> 
> 			VM_BUG_ON_PAGE(page->index + HPAGE_PMD_NR - tail_pages
> 					!= pvec->pages[i]->index, page);
> 
>  - migrate_page_move_mapping() has to be converted too.

Other missing pieces are memfd_wait_for_pins() and memfd_tag_pins()
We need to call page_mapcount() for tail pages there.

-- 
 Kirill A. Shutemov