linux-ext4 - Re: [PATCH 13/13] ext4: Support for synchronous DAX faults

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Message-ID: <20170824123615.GB6187@quack2.suse.cz>
Date:   Thu, 24 Aug 2017 14:36:15 +0200
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, Andy Lutomirski <luto@...nel.org>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Boaz Harrosh <boazh@...app.com>
Subject: Re: [PATCH 13/13] ext4: Support for synchronous DAX faults

On Thu 24-08-17 05:31:26, Christoph Hellwig wrote:
> On Thu, Aug 17, 2017 at 06:08:15PM +0200, Jan Kara wrote:
> > We return IOMAP_F_NEEDDSYNC flag from ext4_iomap_begin() for a
> > synchronous write fault when inode has some uncommitted metadata
> > changes. In the fault handler ext4_dax_fault() we then detect this case,
> > call vfs_fsync_range() to make sure all metadata is committed, and call
> > dax_pfn_mkwrite() to mark PTE as writeable. Note that this will also
> > dirty corresponding radix tree entry which is what we want - fsync(2)
> > will still provide data integrity guarantees for applications not using
> > userspace flushing. And applications using userspace flushing can avoid
> > calling fsync(2) and thus avoid the performance overhead.
> 
> Why is this only wiered up for the huge_fault handler and not the
> regular?

We do handle both. Just ext4 naming is a bit confusing and ext4_dax_fault()
uses ext4_dax_huge_fault() for handling.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR