linux-ext4 - Re: [PATCHv6 08/37] filemap: handle huge pages in do_generic_file

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Date:   Mon, 13 Feb 2017 08:01:17 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>,
        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: [PATCHv6 08/37] filemap: handle huge pages in
 do_generic_file_read()

On Mon, Feb 13, 2017 at 06:33:42PM +0300, Kirill A. Shutemov wrote:
> No. pagecache_get_page() returns subpage. See description of the first
> patch.

Your description says:

> We also change interface for page-cache lookup function:
> 
>   - functions that lookup for pages[1] would return subpages of THP
>     relevant for requested indexes;
> 
>   - functions that lookup for entries[2] would return one entry per-THP
>     and index will point to index of head page (basically, round down to
>     HPAGE_PMD_NR);
> 
> This would provide balanced exposure of multi-order entires to the rest
> of the kernel.
> 
> [1] find_get_pages(), pagecache_get_page(), pagevec_lookup(), etc.
> [2] find_get_entry(), find_get_entries(), pagevec_lookup_entries(), etc.

I'm saying:

> > We got this page from find_get_page(), which gets it from
> > pagecache_get_page(), which gets it from find_get_entry() ... which
> > (unless I'm lost in your patch series) returns the head page.

Am I guilty of debugging documentation rather than code?