diff options
| author | Eric Sandeen <sandeen@redhat.com> | 2010-05-16 04:00:00 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2010-05-16 04:00:00 -0400 |
| commit | c445e3e0a5c2804524dec6e55f66d63f6bc5bc3e (patch) | |
| tree | e4839825628b6d3aa3a9141e32370d5edebcc546 /fs/ext4 | |
| parent | a30eec2a8650a77f754e84b2e15f062fe652baa7 (diff) | |
ext4: don't scan/accumulate more pages than mballoc will allocate
There was a bug reported on RHEL5 that a 10G dd on a 12G box
had a very, very slow sync after that.
At issue was the loop in write_cache_pages scanning all the way
to the end of the 10G file, even though the subsequent call
to mpage_da_submit_io would only actually write a smallish amt; then
we went back to the write_cache_pages loop ... wasting tons of time
in calling __mpage_da_writepage for thousands of pages we would
just revisit (many times) later.
Upstream it's not such a big issue for sys_sync because we get
to the loop with a much smaller nr_to_write, which limits the loop.
However, talking with Aneesh he realized that fsync upstream still
gets here with a very large nr_to_write and we face the same problem.
This patch makes mpage_add_bh_to_extent stop the loop after we've
accumulated 2048 pages, by setting mpd->io_done = 1; which ultimately
causes the write_cache_pages loop to break.
Repeating the test with a dirty_ratio of 80 (to leave something for
fsync to do), I don't see huge IO performance gains, but the reduction
in cpu usage is striking: 80% usage with stock, and 2% with the
below patch. Instrumenting the loop in write_cache_pages clearly
shows that we are wasting time here.
Eventually we need to change mpage_da_map_pages() also submit its I/O
to the block layer, subsuming mpage_da_submit_io(), and then change it
call ext4_get_blocks() multiple times.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'fs/ext4')
| -rw-r--r-- | fs/ext4/inode.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 55bfcd94d1a..89a31e8869c 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2350,6 +2350,15 @@ static void mpage_add_bh_to_extent(struct mpage_da_data *mpd, sector_t next; int nrblocks = mpd->b_size >> mpd->inode->i_blkbits; + /* + * XXX Don't go larger than mballoc is willing to allocate + * This is a stopgap solution. We eventually need to fold + * mpage_da_submit_io() into this function and then call + * ext4_get_blocks() multiple times in a loop + */ + if (nrblocks >= 8*1024*1024/mpd->inode->i_sb->s_blocksize) + goto flush_it; + /* check if thereserved journal credits might overflow */ if (!(EXT4_I(mpd->inode)->i_flags & EXT4_EXTENTS_FL)) { if (nrblocks >= EXT4_MAX_TRANS_DATA) { |