ext4: implement writeback livelock avoidance using page tagging
This is analogous to Jan Kara's commit,
f446daaea9d4a420d16c606f755f3689dcb2d0ce
mm: implement writeback livelock avoidance using page tagging
but since we forked write_cache_pages, we need to reimplement
it there (and in ext4_da_writepages, since range_cyclic handling
was moved to there)
If you start a large buffered IO to a file, and then set
fsync after it, you'll find that fsync does not complete
until the other IO stops.
If you continue re-dirtying the file (say, putting dd
with conv=notrunc in a loop), when fsync finally completes
(after all IO is done), it reports via tracing that
it has written many more pages than the file contains;
in other words it has synced and re-synced pages in
the file multiple times.
This then leads to problems with our writeback_index
update, since it advances it by pages written, and
essentially sets writeback_index off the end of the
file...
With the following patch, we only sync as much as was
dirty at the time of the sync.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 6671fcb..c9ea95b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2809,16 +2809,21 @@
pgoff_t index;
pgoff_t end; /* Inclusive */
long nr_to_write = wbc->nr_to_write;
+ int tag;
pagevec_init(&pvec, 0);
index = wbc->range_start >> PAGE_CACHE_SHIFT;
end = wbc->range_end >> PAGE_CACHE_SHIFT;
+ if (wbc->sync_mode == WB_SYNC_ALL)
+ tag = PAGECACHE_TAG_TOWRITE;
+ else
+ tag = PAGECACHE_TAG_DIRTY;
+
while (!done && (index <= end)) {
int i;
- nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
- PAGECACHE_TAG_DIRTY,
+ nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
if (nr_pages == 0)
break;
@@ -2923,6 +2928,7 @@
long desired_nr_to_write, nr_to_writebump = 0;
loff_t range_start = wbc->range_start;
struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
+ pgoff_t end;
trace_ext4_da_writepages(inode, wbc);
@@ -2958,8 +2964,11 @@
wbc->range_start = index << PAGE_CACHE_SHIFT;
wbc->range_end = LLONG_MAX;
wbc->range_cyclic = 0;
- } else
+ end = -1;
+ } else {
index = wbc->range_start >> PAGE_CACHE_SHIFT;
+ end = wbc->range_end >> PAGE_CACHE_SHIFT;
+ }
/*
* This works around two forms of stupidity. The first is in
@@ -3000,6 +3009,9 @@
pages_skipped = wbc->pages_skipped;
retry:
+ if (wbc->sync_mode == WB_SYNC_ALL)
+ tag_pages_for_writeback(mapping, index, end);
+
while (!ret && wbc->nr_to_write > 0) {
/*