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gfs2: add flag REQ_PRIO for metadata I/O 

When gfs2 does metadata I/O, only REQ_META is used as a metadata hint of
the bio. But flag REQ_META is just a hint for block trace, not for block
layer code to handle a bio as metadata request.

For some of metadata I/Os of gfs2, A REQ_PRIO flag on the metadata bio
would be very informative to block layer code. For example, if bcache is
used as a I/O cache for gfs2, it will be possible for bcache code to get
the hint and cache the pre-fetched metadata blocks on cache device. This
behavior may be helpful to improve metadata I/O performance if the
following requests hit the cache.

Here are the locations in gfs2 code where a REQ_PRIO flag should be added,
- All places where REQ_READAHEAD is used, gfs2 code uses this flag for
  metadata read ahead.
- In gfs2_meta_rq() where the first metadata block is read in.
- In gfs2_write_buf_to_page(), read in quota metadata blocks to have them
  up to date.
These metadata blocks are probably to be accessed again in future, adding
a REQ_PRIO flag may have bcache to keep such metadata in fast cache
device. For system without a cache layer, REQ_PRIO can still provide hint
to block layer to handle metadata requests more properly.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
This commit is contained in:
Coly Li 2017-07-21 07:48:22 -05:00 committed by Bob Peterson
parent e7cb550d79
commit e477b24b50
4 changed files with 11 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
fs/gfs2/bmap.c
View File

@ -291,8 +291,9 @@ static void gfs2_metapath_ra(struct gfs2_glock *gl,
if (trylock_buffer(rabh)) {
if (!buffer_uptodate(rabh)) {
rabh->b_end_io = end_buffer_read_sync;
submit_bh(REQ_OP_READ, REQ_RAHEAD | REQ_META,
rabh);
submit_bh(REQ_OP_READ,
REQ_RAHEAD | REQ_META | REQ_PRIO,
rabh);
continue;
}
unlock_buffer(rabh);

4
fs/gfs2/dir.c
View File

@ -1514,7 +1514,9 @@ static void gfs2_dir_readahead(struct inode *inode, unsigned hsize, u32 index,
continue;
}
bh->b_end_io = end_buffer_read_sync;
submit_bh(REQ_OP_READ, REQ_RAHEAD | REQ_META, bh);
submit_bh(REQ_OP_READ,
REQ_RAHEAD | REQ_META | REQ_PRIO,
bh);
continue;
}
brelse(bh);

6
fs/gfs2/meta_io.c
View File

@ -453,7 +453,7 @@ struct buffer_head *gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
if (buffer_uptodate(first_bh))
goto out;
if (!buffer_locked(first_bh))
ll_rw_block(REQ_OP_READ, REQ_META, 1, &first_bh);
ll_rw_block(REQ_OP_READ, REQ_META | REQ_PRIO, 1, &first_bh);
dblock++;
extlen--;
@ -462,7 +462,9 @@ struct buffer_head *gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
bh = gfs2_getbuf(gl, dblock, CREATE);
if (!buffer_uptodate(bh) && !buffer_locked(bh))
ll_rw_block(REQ_OP_READ, REQ_RAHEAD | REQ_META, 1, &bh);
ll_rw_block(REQ_OP_READ,
REQ_RAHEAD | REQ_META | REQ_PRIO,
1, &bh);
brelse(bh);
dblock++;
extlen--;

2
fs/gfs2/quota.c
View File

@ -730,7 +730,7 @@ static int gfs2_write_buf_to_page(struct gfs2_inode *ip, unsigned long index,
if (PageUptodate(page))
set_buffer_uptodate(bh);
if (!buffer_uptodate(bh)) {
ll_rw_block(REQ_OP_READ, REQ_META, 1, &bh);
ll_rw_block(REQ_OP_READ, REQ_META | REQ_PRIO, 1, &bh);
wait_on_buffer(bh);
if (!buffer_uptodate(bh))
goto unlock_out;