linux-kernel - Re: [PATCH v3 0/2] mm,thp: Add filemap_huge

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Message-ID: <20190731102053.GZ7689@dread.disaster.area>
Date:   Wed, 31 Jul 2019 20:20:53 +1000
From:   Dave Chinner <david@...morbit.com>
To:     William Kucharski <william.kucharski@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Bob Kasten <robert.a.kasten@...el.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Chad Mynhier <chad.mynhier@...cle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Johannes Weiner <jweiner@...com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v3 0/2] mm,thp: Add filemap_huge_fault() for THP

On Wed, Jul 31, 2019 at 02:25:11AM -0600, William Kucharski wrote:
> This set of patches is the first step towards a mechanism for automatically
> mapping read-only text areas of appropriate size and alignment to THPs
> whenever possible.
> 
> For now, the central routine, filemap_huge_fault(), amd various support
> routines are only included if the experimental kernel configuration option
> 
> 	RO_EXEC_FILEMAP_HUGE_FAULT_THP
> 
> is enabled.
> 
> This is because filemap_huge_fault() is dependent upon the
> address_space_operations vector readpage() pointing to a routine that will
> read and fill an entire large page at a time without poulluting the page
> cache with PAGESIZE entries

How is the readpage code supposed to stuff a THP page into a bio?

i.e. Do bio's support huge pages, and if not, what is needed to
stuff a huge page in a bio chain?

Once you can answer that question, you should be able to easily
convert the iomap_readpage/iomap_readpage_actor code to support THP
pages without having to care about much else as iomap_readpage()
is already coded in a way that will iterate IO over the entire THP
for you....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com