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Date: Wed, 20 May 2020 15:37:28 +0200 From: Jan Kara <jack@...e.cz> To: ira.weiny@...el.com Cc: linux-ext4@...r.kernel.org, Andreas Dilger <adilger.kernel@...ger.ca>, "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>, Eric Biggers <ebiggers@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Dan Williams <dan.j.williams@...el.com>, Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>, "Darrick J. Wong" <darrick.wong@...cle.com>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH V3 4/8] fs/ext4: Update ext4_should_use_dax() On Tue 19-05-20 22:57:49, ira.weiny@...el.com wrote: > From: Ira Weiny <ira.weiny@...el.com> > > S_DAX should only be enabled when the underlying block device supports > dax. > > Change ext4_should_use_dax() to check for device support prior to the > over riding mount option. > > While we are at it change the function to ext4_should_enable_dax() as > this better reflects the ask as well as matches xfs. > > Reviewed-by: Jan Kara <jack@...e.cz> > Signed-off-by: Ira Weiny <ira.weiny@...el.com> ... > @@ -4412,7 +4410,13 @@ static bool ext4_should_use_dax(struct inode *inode) > return false; > if (ext4_test_inode_flag(inode, EXT4_INODE_VERITY)) > return false; > - return true; > + if (!bdev_dax_supported(inode->i_sb->s_bdev, > + inode->i_sb->s_blocksize)) > + return false; > + if (test_opt(inode->i_sb, DAX_ALWAYS)) > + return true; > + > + return false; > } Now that I think about it - shouldn't we rather cache the result of bdev_dax_supported() in sb on mount and then just check the flag here? Because bdev_dax_supported() isn't exactly cheap (it does a lot of checks and mappings, tries to read from the pmem, ...). Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
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