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Date: Wed, 20 May 2020 12:40:50 -0700 From: Ira Weiny <ira.weiny@...el.com> To: Jan Kara <jack@...e.cz> Cc: linux-ext4@...r.kernel.org, Andreas Dilger <adilger.kernel@...ger.ca>, "Theodore Y. Ts'o" <tytso@....edu>, 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 Wed, May 20, 2020 at 03:37:28PM +0200, Jan Kara wrote: > 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, ...). Sounds reasonable. Not sure which flags are appropriate. So add it here? diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 1a3daf2d18ef..0b4db9ce7756 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1979,6 +1979,7 @@ static inline bool ext4_has_incompat_features(struct super_block *sb) */ #define EXT4_FLAGS_RESIZING 0 #define EXT4_FLAGS_SHUTDOWN 1 +#define EXT4_FLAGS_BDEV_IS_DAX 2 static inline int ext4_forced_shutdown(struct ext4_sb_info *sbi) {
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