From: Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH] mm: replace FAULT_FLAG_SIZE with parameter to huge_fault
Date: Mon, 6 Feb 2017 08:24:48 -0800
Message-ID: <CAPcyv4jHYR2-_SgD7a6ab5vWigYsDoSb7FZdTchP8Xg+BF-2yg@mail.gmail.com>
References: <148615748258.43180.1690152053774975329.stgit@djiang5-desk3.ch.intel.com>
 <20170206143648.GA461@infradead.org>
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Cc: Dave Jiang <dave.jiang@intel.com>, 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>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Jan Kara <jack@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>, linux-ext4 <linux-ext4@vger.kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>
To: Christoph Hellwig <hch@infradead.org>
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In-Reply-To: <20170206143648.GA461@infradead.org>
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On Mon, Feb 6, 2017 at 6:36 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Fri, Feb 03, 2017 at 02:31:22PM -0700, Dave Jiang wrote:
>> Since the introduction of FAULT_FLAG_SIZE to the vm_fault flag, it has
>> been somewhat painful with getting the flags set and removed at the
>> correct locations. More than one kernel oops was introduced due to
>> difficulties of getting the placement correctly. Removing the flag
>> values and introducing an input parameter to huge_fault that indicates
>> the size of the page entry. This makes the code easier to trace and
>> should avoid the issues we see with the fault flags where removal of the
>> flag was necessary in the fallback paths.
>
> Why is this not in struct vm_fault?

Because this is easier to read and harder to get wrong. Same arguments
as getting rid of struct blk_dax_ctl.

> Also can be use this opportunity
> to fold ->huge_fault into ->fault?

Hmm, yes, just need a scheme to not attempt huge_faults on pte-only handlers.

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