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Message-ID: <20110505181032.GA21360@parisc-linux.org>
Date: Thu, 5 May 2011 12:10:32 -0600
From: Matthew Wilcox <matthew@....cx>
To: Andreas Dilger <adilger@...ger.ca>
Cc: "Gao, Yunpeng" <yunpeng.gao@...el.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: Is it possible for the ext4/btrfs file system to pass some
context related info to low level block driver?
On Wed, May 04, 2011 at 08:51:39AM -0600, Andreas Dilger wrote:
> I was aware of REQ_META, but I didn't know there was any benefit to
> using it. I think it would be easy to set REQ_META on all ext4 metadata
> if there was a reason to do so.
The CFQ ioscheduler pays attention to it (prioritising metadata accesses
over data accesses), and blocktrace will print an 'M' for metadata
requests if it's set, so I think that's two excellent reasons to set
REQ_META today.
However, ext3, ext4, and XFS already use it:
fs/ext3/inode.c:1105: ll_rw_block(READ_META, 1, &bh);
fs/ext3/inode.c:2754: submit_bh(READ_META, bh);
fs/ext3/namei.c:924: ll_rw_block(READ_META, 1, &bh);
fs/ext4/inode.c:1500: ll_rw_block(READ_META, 1, &bh);
fs/ext4/inode.c:4775: submit_bh(READ_META, bh);
fs/ext4/namei.c:924: ll_rw_block(READ_META, 1, &bh);
fs/gfs2/log.c:597: submit_bh(WRITE_SYNC | REQ_META, bh);
fs/gfs2/log.c:599: submit_bh(WRITE_FLUSH_FUA | REQ_META, bh);
fs/gfs2/meta_io.c:39: int write_op = REQ_META |
fs/gfs2/meta_io.c:228: submit_bh(READ_SYNC | REQ_META, bh);
fs/gfs2/meta_io.c:435: ll_rw_block(READ_SYNC | REQ_META, 1, &first_bh);
fs/gfs2/ops_fstype.c:221: submit_bio(READ_SYNC | REQ_META, bio);
fs/gfs2/quota.c:710: ll_rw_block(READ_META, 1, &bh);
fs/xfs/linux-2.6/xfs_buf.c:1321: rw = (bp->b_flags & XBF_WRITE) ? WRITE_META : READ_META;
include/linux/fs.h:164:#define READ_META (READ | REQ_META)
include/linux/fs.h:168:#define WRITE_META (WRITE | REQ_META)
btrfs seems to not use REQ_META yet. *poke* *poke* :-)
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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