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Message-ID: <20130216023251.GA11195@gmail.com> Date: Sat, 16 Feb 2013 10:32:51 +0800 From: Zheng Liu <gnehzuil.liu@...il.com> To: Theodore Ts'o <tytso@....edu> Cc: Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com> Subject: Re: [PATCH 05/10 v5] ext4: lookup block mapping in extent status tree On Fri, Feb 15, 2013 at 12:25:49PM -0500, Theodore Ts'o wrote: > On Fri, Feb 15, 2013 at 03:06:26PM +0800, Zheng Liu wrote: > > > > I am planning to refine the get_block_t and *map_blocks functions. At > > that time I will try to fix this problem. > > Note that get_block_t can't be changed without disrupting the Direct > I/O functions which are generic VFS functions. There's been talk of > trying to clean up DIO, but it will probably require building a > parallel infrastructure in the generic layer, and then transitioning > individual file systems over to it. It is definitely a mess, but it's > going to be a very tricky problem. I suspect we'll be talking about > it at LSF/MM. > > One thing thing which might be an interesting thing to do that > wouldn't require wholesale changes to generic code would be to > transition ext4_readpages() to use fs/ext4/page-io.c. Not for this > merge window, in all likelihood, but right now we are calling > ext4_get_block() for every single page that we read in, while is > wasteful. It would be nice if ext4_readpages() called > ext4_map_blocks() for each extent, and then submitted it using the > page-io.c functions so we don't end up calling into ext4_map_blocks() > quite as much. > > That will ease our scalability and remove locking overhead, in > addition to saving CPU for the buffered I/O readpages path. > Eventually it would be good to do this for DIO as well, but that's > going to require a lot more work, and coordination with the developers > of btrfs, xfs, etc. To be honest, my initial idea is only to split ext4_map_blocks into ext4_map_blocks_read and ext4_map_blocks_write, and do some cleanups. Thanks for your suggestions. I will look at it carefully after the patch series of extent status tree has been applied. Thanks, - Zheng -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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