Commit 6e6938b6 authored by Wu Fengguang's avatar Wu Fengguang

writeback: introduce .tagged_writepages for the WB_SYNC_NONE sync stage

sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
WB_SYNC_ALL sync. Identify the first stage with .tagged_writepages and
do livelock prevention for it, too.

Jan's commit f446daae ("mm: implement writeback livelock avoidance
using page tagging") is a partial fix in that it only fixed the
WB_SYNC_ALL phase livelock.

Although ext4 is tested to no longer livelock with commit f446daae,
it may due to some "redirty_tail() after pages_skipped" effect which
is by no means a guarantee for _all_ the file systems.

Note that writeback_inodes_sb() is called by not only sync(), they are
treated the same because the other callers also need livelock prevention.

Impact:  It changes the order in which pages/inodes are synced to disk.
Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
until finished with the current inode.
Acked-by: default avatarJan Kara <jack@suse.cz>
CC: Dave Chinner <david@fromorbit.com>
Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
parent 59c5f46f
......@@ -2741,7 +2741,7 @@ static int write_cache_pages_da(struct address_space *mapping,
index = wbc->range_start >> PAGE_CACHE_SHIFT;
end = wbc->range_end >> PAGE_CACHE_SHIFT;
if (wbc->sync_mode == WB_SYNC_ALL)
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
......@@ -2973,7 +2973,7 @@ static int ext4_da_writepages(struct address_space *mapping,
}
retry:
if (wbc->sync_mode == WB_SYNC_ALL)
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag_pages_for_writeback(mapping, index, end);
while (!ret && wbc->nr_to_write > 0) {
......
......@@ -36,6 +36,7 @@ struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
enum writeback_sync_modes sync_mode;
unsigned int tagged_writepages:1;
unsigned int for_kupdate:1;
unsigned int range_cyclic:1;
unsigned int for_background:1;
......@@ -650,6 +651,7 @@ static long wb_writeback(struct bdi_writeback *wb,
{
struct writeback_control wbc = {
.sync_mode = work->sync_mode,
.tagged_writepages = work->tagged_writepages,
.older_than_this = NULL,
.for_kupdate = work->for_kupdate,
.for_background = work->for_background,
......@@ -657,7 +659,7 @@ static long wb_writeback(struct bdi_writeback *wb,
};
unsigned long oldest_jif;
long wrote = 0;
long write_chunk;
long write_chunk = MAX_WRITEBACK_PAGES;
struct inode *inode;
if (wbc.for_kupdate) {
......@@ -683,9 +685,7 @@ static long wb_writeback(struct bdi_writeback *wb,
* (quickly) tag currently dirty pages
* (maybe slowly) sync all tagged pages
*/
if (wbc.sync_mode == WB_SYNC_NONE)
write_chunk = MAX_WRITEBACK_PAGES;
else
if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_writepages)
write_chunk = LONG_MAX;
wbc.wb_start = jiffies; /* livelock avoidance */
......@@ -1188,10 +1188,11 @@ void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr)
{
DECLARE_COMPLETION_ONSTACK(done);
struct wb_writeback_work work = {
.sb = sb,
.sync_mode = WB_SYNC_NONE,
.done = &done,
.nr_pages = nr,
.sb = sb,
.sync_mode = WB_SYNC_NONE,
.tagged_writepages = 1,
.done = &done,
.nr_pages = nr,
};
WARN_ON(!rwsem_is_locked(&sb->s_umount));
......
......@@ -47,6 +47,7 @@ struct writeback_control {
unsigned encountered_congestion:1; /* An output: a queue is full */
unsigned for_kupdate:1; /* A kupdate writeback */
unsigned for_background:1; /* A background writeback */
unsigned tagged_writepages:1; /* tag-and-write to avoid livelock */
unsigned for_reclaim:1; /* Invoked from the page allocator */
unsigned range_cyclic:1; /* range_start is cyclic */
unsigned more_io:1; /* more io to be dispatched */
......
......@@ -892,12 +892,12 @@ int write_cache_pages(struct address_space *mapping,
range_whole = 1;
cycled = 1; /* ignore range_cyclic tests */
}
if (wbc->sync_mode == WB_SYNC_ALL)
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
retry:
if (wbc->sync_mode == WB_SYNC_ALL)
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag_pages_for_writeback(mapping, index, end);
done_index = index;
while (!done && (index <= end)) {
......
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