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authorJan Kara <jack@suse.cz>2017-04-30 18:29:10 -0400
committerTheodore Ts'o <tytso@mit.edu>2017-04-30 18:29:10 -0400
commitdddbd6ac8f25b2d61e3e1c7134e3b3e1b9cd8670 (patch)
tree0c7faeba079cc793bee59b1c265e01c777cf9f70 /fs/ext4
parent85c8f176a6111ecde9c158109989dbd445a0e59a (diff)
ext4: avoid unnecessary transaction stalls during writeback
Currently ext4_writepages() submits all pages with transaction started. When no page needs block allocation or extent conversion we can submit all dirty pages in the inode while holding a single transaction handle and when device is congested this can take significant amount of time. Thus ext4_writepages() can block transaction commits for extended periods of time. Take for example a simple benchmark simulating PostgreSQL database (pgioperf in mmtest). The benchmark runs 16 processes doing random reads from a huge file, one process doing random writes to the huge file, and one process doing sequential writes to a small files and frequently running fsync. With unpatched kernel transaction commits take on average ~18s with standard deviation of ~41s, top 5 commit times are: 274.466639s, 126.467347s, 86.992429s, 34.351563s, 31.517653s. After this patch transaction commits take on average 0.1s with standard deviation of 0.15s, top 5 commit times are: 0.563792s, 0.519980s, 0.509841s, 0.471700s, 0.469899s [ Modified so we use an explicit do_map flag instead of relying on io_end not being allocated, the since io_end->inode is needed for I/O error handling. -- tytso ] Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'fs/ext4')
-rw-r--r--fs/ext4/inode.c35
1 files changed, 35 insertions, 0 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 88203ae5b154..2a4507deb925 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1643,6 +1643,7 @@ struct mpage_da_data {
*/
struct ext4_map_blocks map;
struct ext4_io_submit io_submit; /* IO submission data */
+ unsigned int do_map:1;
};
static void mpage_release_unused_pages(struct mpage_da_data *mpd,
@@ -2179,6 +2180,9 @@ static bool mpage_add_bh_to_extent(struct mpage_da_data *mpd, ext4_lblk_t lblk,
/* First block in the extent? */
if (map->m_len == 0) {
+ /* We cannot map unless handle is started... */
+ if (!mpd->do_map)
+ return false;
map->m_lblk = lblk;
map->m_len = 1;
map->m_flags = bh->b_state & BH_FLAGS;
@@ -2231,6 +2235,9 @@ static int mpage_process_page_bufs(struct mpage_da_data *mpd,
/* Found extent to map? */
if (mpd->map.m_len)
return 0;
+ /* Buffer needs mapping and handle is not started? */
+ if (!mpd->do_map)
+ return 0;
/* Everything mapped so far and we hit EOF */
break;
}
@@ -2747,6 +2754,29 @@ retry:
tag_pages_for_writeback(mapping, mpd.first_page, mpd.last_page);
done = false;
blk_start_plug(&plug);
+
+ /*
+ * First writeback pages that don't need mapping - we can avoid
+ * starting a transaction unnecessarily and also avoid being blocked
+ * in the block layer on device congestion while having transaction
+ * started.
+ */
+ mpd.do_map = 0;
+ mpd.io_submit.io_end = ext4_init_io_end(inode, GFP_KERNEL);
+ if (!mpd.io_submit.io_end) {
+ ret = -ENOMEM;
+ goto unplug;
+ }
+ ret = mpage_prepare_extent_to_map(&mpd);
+ /* Submit prepared bio */
+ ext4_io_submit(&mpd.io_submit);
+ ext4_put_io_end_defer(mpd.io_submit.io_end);
+ mpd.io_submit.io_end = NULL;
+ /* Unlock pages we didn't use */
+ mpage_release_unused_pages(&mpd, false);
+ if (ret < 0)
+ goto unplug;
+
while (!done && mpd.first_page <= mpd.last_page) {
/* For each extent of pages we use new io_end */
mpd.io_submit.io_end = ext4_init_io_end(inode, GFP_KERNEL);
@@ -2775,8 +2805,10 @@ retry:
wbc->nr_to_write, inode->i_ino, ret);
/* Release allocated io_end */
ext4_put_io_end(mpd.io_submit.io_end);
+ mpd.io_submit.io_end = NULL;
break;
}
+ mpd.do_map = 1;
trace_ext4_da_write_pages(inode, mpd.first_page, mpd.wbc);
ret = mpage_prepare_extent_to_map(&mpd);
@@ -2807,6 +2839,7 @@ retry:
if (!ext4_handle_valid(handle) || handle->h_sync == 0) {
ext4_journal_stop(handle);
handle = NULL;
+ mpd.do_map = 0;
}
/* Submit prepared bio */
ext4_io_submit(&mpd.io_submit);
@@ -2824,6 +2857,7 @@ retry:
ext4_journal_stop(handle);
} else
ext4_put_io_end(mpd.io_submit.io_end);
+ mpd.io_submit.io_end = NULL;
if (ret == -ENOSPC && sbi->s_journal) {
/*
@@ -2839,6 +2873,7 @@ retry:
if (ret)
break;
}
+unplug:
blk_finish_plug(&plug);
if (!ret && !cycled && wbc->nr_to_write > 0) {
cycled = 1;