From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH] mm: replace FAULT_FLAG_SIZE with parameter to huge_fault
Date: Tue, 7 Feb 2017 20:40:42 +0300
Message-ID: <20170207174042.GB5578@node.shutemov.name>
References: <148615748258.43180.1690152053774975329.stgit@djiang5-desk3.ch.intel.com>
 <20170206143648.GA461@infradead.org>
 <CAPcyv4jHYR2-_SgD7a6ab5vWigYsDoSb7FZdTchP8Xg+BF-2yg@mail.gmail.com>
 <20170206172731.GA17515@infradead.org>
 <CAPcyv4hiwWebCT=qPccKqaQKAHydMYsg9+=pYh=SPkNzakLc1A@mail.gmail.com>
 <20170207084411.GA527@node.shutemov.name>
 <CAPcyv4h1LvbEqBi=F=BTtLrHHOvAH3MU2OBDs444-dzwNyupFQ@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Christoph Hellwig <hch@infradead.org>,
	Matthew Wilcox <mawilcox@microsoft.com>,
	"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	linux-xfs@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
	Vlastimil Babka <vbabka@suse.cz>, Jan Kara <jack@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-ext4 <linux-ext4@vger.kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Return-path: <owner-linux-mm@kvack.org>
Content-Disposition: inline
In-Reply-To: <CAPcyv4h1LvbEqBi=F=BTtLrHHOvAH3MU2OBDs444-dzwNyupFQ@mail.gmail.com>
Sender: owner-linux-mm@kvack.org
List-Id: linux-ext4.vger.kernel.org

On Tue, Feb 07, 2017 at 08:56:56AM -0800, Dan Williams wrote:
> On Tue, Feb 7, 2017 at 12:44 AM, Kirill A. Shutemov
> <kirill@shutemov.name> wrote:
> > On Mon, Feb 06, 2017 at 09:30:22AM -0800, Dan Williams wrote:
> >> On Mon, Feb 6, 2017 at 9:27 AM, Christoph Hellwig <hch@infradead.org> wrote:
> >> > On Mon, Feb 06, 2017 at 08:24:48AM -0800, Dan Williams wrote:
> >> >> > Also can be use this opportunity
> >> >> > to fold ->huge_fault into ->fault?
> >
> > BTW, for tmpfs we already use ->fault for both small and huge pages.
> > If ->fault returned THP, core mm look if it's possible to map the page as
> > huge in this particular VMA (due to size/alignment). If yes mm maps the
> > page with PMD, if not fallback to PTE.
> >
> > I think it would be nice to do the same for DAX: filesystem provides core
> > mm with largest page this part of file can be mapped with (base aligned
> > address + lenght for DAX) and core mm sort out the rest.
> 
> For DAX we would need plumb pfn_t into the core mm so that we have the
> PFN_DEV and PFN_MAP flags beyond the raw pfn.

Sounds good to me.

> >> >> Hmm, yes, just need a scheme to not attempt huge_faults on pte-only handlers.
> >> >
> >> > Do we need anything more than checking vma->vm_flags for VM_HUGETLB?
> >>
> >> s/VM_HUGETLB/VM_HUGEPAGE/
> >>
> >> ...but yes as long as we specify that a VM_HUGEPAGE handler must
> >> minimally handle pud and pmd.
> >
> > VM_HUGEPAGE is result of MADV_HUGEPAGE. It's not required to have THP in
> > the VMA.
> 
> Filesystem-DAX and Device-DAX specify VM_HUGEPAGE by default.

But why? Looks like abuse of the flag.

-- 
 Kirill A. Shutemov

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>