writeback: make writeback_control.nr_to_write straight
Pass struct wb_writeback_work all the way down to writeback_sb_inodes(),
and initialize the struct writeback_control there.
struct writeback_control is basically designed to control writeback of a
single file, but we keep abuse it for writing multiple files in
writeback_sb_inodes() and its callers.
It immediately clean things up, e.g. suddenly wbc.nr_to_write vs
work->nr_pages starts to make sense, and instead of saving and restoring
pages_skipped in writeback_sb_inodes it can always start with a clean
zero value.
It also makes a neat IO pattern change: large dirty files are now
written in the full 4MB writeback chunk size, rather than whatever
remained quota in wbc->nr_to_write.
Acked-by: Jan Kara <jack@suse.cz>
Proposed-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 6caa982..2c947da 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -30,11 +30,21 @@
#include "internal.h"
/*
+ * The maximum number of pages to writeout in a single bdi flush/kupdate
+ * operation. We do this so we don't hold I_SYNC against an inode for
+ * enormous amounts of time, which would block a userspace task which has
+ * been forced to throttle against that inode. Also, the code reevaluates
+ * the dirty each time it has written this many pages.
+ */
+#define MAX_WRITEBACK_PAGES 1024L
+
+/*
* Passed into wb_writeback(), essentially a subset of writeback_control
*/
struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
+ unsigned long *older_than_this;
enum writeback_sync_modes sync_mode;
unsigned int tagged_writepages:1;
unsigned int for_kupdate:1;
@@ -472,7 +482,6 @@
* No need to add it back to the LRU.
*/
list_del_init(&inode->i_wb_list);
- wbc->inodes_written++;
}
}
inode_sync_complete(inode);
@@ -506,6 +515,31 @@
return false;
}
+static long writeback_chunk_size(struct wb_writeback_work *work)
+{
+ long pages;
+
+ /*
+ * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
+ * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
+ * here avoids calling into writeback_inodes_wb() more than once.
+ *
+ * The intended call sequence for WB_SYNC_ALL writeback is:
+ *
+ * wb_writeback()
+ * writeback_sb_inodes() <== called only once
+ * write_cache_pages() <== called once for each inode
+ * (quickly) tag currently dirty pages
+ * (maybe slowly) sync all tagged pages
+ */
+ if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
+ pages = LONG_MAX;
+ else
+ pages = min(MAX_WRITEBACK_PAGES, work->nr_pages);
+
+ return pages;
+}
+
/*
* Write a portion of b_io inodes which belong to @sb.
*
@@ -513,18 +547,30 @@
* inodes. Otherwise write only ones which go sequentially
* in reverse order.
*
- * Return 1, if the caller writeback routine should be
- * interrupted. Otherwise return 0.
+ * Return the number of pages and/or inodes written.
*/
-static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
- struct writeback_control *wbc, bool only_this_sb)
+static long writeback_sb_inodes(struct super_block *sb,
+ struct bdi_writeback *wb,
+ struct wb_writeback_work *work)
{
+ struct writeback_control wbc = {
+ .sync_mode = work->sync_mode,
+ .tagged_writepages = work->tagged_writepages,
+ .for_kupdate = work->for_kupdate,
+ .for_background = work->for_background,
+ .range_cyclic = work->range_cyclic,
+ .range_start = 0,
+ .range_end = LLONG_MAX,
+ };
+ unsigned long start_time = jiffies;
+ long write_chunk;
+ long wrote = 0; /* count both pages and inodes */
+
while (!list_empty(&wb->b_io)) {
- long pages_skipped;
struct inode *inode = wb_inode(wb->b_io.prev);
if (inode->i_sb != sb) {
- if (only_this_sb) {
+ if (work->sb) {
/*
* We only want to write back data for this
* superblock, move all inodes not belonging
@@ -539,7 +585,7 @@
* Bounce back to the caller to unpin this and
* pin the next superblock.
*/
- return 0;
+ break;
}
/*
@@ -553,12 +599,18 @@
requeue_io(inode, wb);
continue;
}
-
__iget(inode);
+ write_chunk = writeback_chunk_size(work);
+ wbc.nr_to_write = write_chunk;
+ wbc.pages_skipped = 0;
- pages_skipped = wbc->pages_skipped;
- writeback_single_inode(inode, wb, wbc);
- if (wbc->pages_skipped != pages_skipped) {
+ writeback_single_inode(inode, wb, &wbc);
+
+ work->nr_pages -= write_chunk - wbc.nr_to_write;
+ wrote += write_chunk - wbc.nr_to_write;
+ if (!(inode->i_state & I_DIRTY))
+ wrote++;
+ if (wbc.pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
@@ -570,17 +622,25 @@
iput(inode);
cond_resched();
spin_lock(&wb->list_lock);
- if (wbc->nr_to_write <= 0)
- return 1;
+ /*
+ * bail out to wb_writeback() often enough to check
+ * background threshold and other termination conditions.
+ */
+ if (wrote) {
+ if (time_is_before_jiffies(start_time + HZ / 10UL))
+ break;
+ if (work->nr_pages <= 0)
+ break;
+ }
}
- /* b_io is empty */
- return 1;
+ return wrote;
}
-static void __writeback_inodes_wb(struct bdi_writeback *wb,
- struct writeback_control *wbc)
+static long __writeback_inodes_wb(struct bdi_writeback *wb,
+ struct wb_writeback_work *work)
{
- int ret = 0;
+ unsigned long start_time = jiffies;
+ long wrote = 0;
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
@@ -590,33 +650,37 @@
requeue_io(inode, wb);
continue;
}
- ret = writeback_sb_inodes(sb, wb, wbc, false);
+ wrote += writeback_sb_inodes(sb, wb, work);
drop_super(sb);
- if (ret)
- break;
+ /* refer to the same tests at the end of writeback_sb_inodes */
+ if (wrote) {
+ if (time_is_before_jiffies(start_time + HZ / 10UL))
+ break;
+ if (work->nr_pages <= 0)
+ break;
+ }
}
/* Leave any unwritten inodes on b_io */
+ return wrote;
}
-void writeback_inodes_wb(struct bdi_writeback *wb,
- struct writeback_control *wbc)
+long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages)
{
+ struct wb_writeback_work work = {
+ .nr_pages = nr_pages,
+ .sync_mode = WB_SYNC_NONE,
+ .range_cyclic = 1,
+ };
+
spin_lock(&wb->list_lock);
if (list_empty(&wb->b_io))
- queue_io(wb, wbc->older_than_this);
- __writeback_inodes_wb(wb, wbc);
+ queue_io(wb, NULL);
+ __writeback_inodes_wb(wb, &work);
spin_unlock(&wb->list_lock);
-}
-/*
- * The maximum number of pages to writeout in a single bdi flush/kupdate
- * operation. We do this so we don't hold I_SYNC against an inode for
- * enormous amounts of time, which would block a userspace task which has
- * been forced to throttle against that inode. Also, the code reevaluates
- * the dirty each time it has written this many pages.
- */
-#define MAX_WRITEBACK_PAGES 1024
+ return nr_pages - work.nr_pages;
+}
static inline bool over_bground_thresh(void)
{
@@ -646,42 +710,13 @@
static long wb_writeback(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
- 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,
- .range_cyclic = work->range_cyclic,
- };
+ long nr_pages = work->nr_pages;
unsigned long oldest_jif;
- long wrote = 0;
- long write_chunk = MAX_WRITEBACK_PAGES;
struct inode *inode;
-
- if (!wbc.range_cyclic) {
- wbc.range_start = 0;
- wbc.range_end = LLONG_MAX;
- }
-
- /*
- * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
- * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
- * here avoids calling into writeback_inodes_wb() more than once.
- *
- * The intended call sequence for WB_SYNC_ALL writeback is:
- *
- * wb_writeback()
- * writeback_sb_inodes() <== called only once
- * write_cache_pages() <== called once for each inode
- * (quickly) tag currently dirty pages
- * (maybe slowly) sync all tagged pages
- */
- if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_writepages)
- write_chunk = LONG_MAX;
+ long progress;
oldest_jif = jiffies;
- wbc.older_than_this = &oldest_jif;
+ work->older_than_this = &oldest_jif;
spin_lock(&wb->list_lock);
for (;;) {
@@ -711,24 +746,17 @@
if (work->for_kupdate) {
oldest_jif = jiffies -
msecs_to_jiffies(dirty_expire_interval * 10);
- wbc.older_than_this = &oldest_jif;
+ work->older_than_this = &oldest_jif;
}
- wbc.nr_to_write = write_chunk;
- wbc.pages_skipped = 0;
- wbc.inodes_written = 0;
-
- trace_wbc_writeback_start(&wbc, wb->bdi);
+ trace_writeback_start(wb->bdi, work);
if (list_empty(&wb->b_io))
- queue_io(wb, wbc.older_than_this);
+ queue_io(wb, work->older_than_this);
if (work->sb)
- writeback_sb_inodes(work->sb, wb, &wbc, true);
+ progress = writeback_sb_inodes(work->sb, wb, work);
else
- __writeback_inodes_wb(wb, &wbc);
- trace_wbc_writeback_written(&wbc, wb->bdi);
-
- work->nr_pages -= write_chunk - wbc.nr_to_write;
- wrote += write_chunk - wbc.nr_to_write;
+ progress = __writeback_inodes_wb(wb, work);
+ trace_writeback_written(wb->bdi, work);
/*
* Did we write something? Try for more
@@ -738,9 +766,7 @@
* mean the overall work is done. So we keep looping as long
* as made some progress on cleaning pages or inodes.
*/
- if (wbc.nr_to_write < write_chunk)
- continue;
- if (wbc.inodes_written)
+ if (progress)
continue;
/*
* No more inodes for IO, bail
@@ -753,8 +779,8 @@
* we'll just busyloop.
*/
if (!list_empty(&wb->b_more_io)) {
+ trace_writeback_wait(wb->bdi, work);
inode = wb_inode(wb->b_more_io.prev);
- trace_wbc_writeback_wait(&wbc, wb->bdi);
spin_lock(&inode->i_lock);
inode_wait_for_writeback(inode, wb);
spin_unlock(&inode->i_lock);
@@ -762,7 +788,7 @@
}
spin_unlock(&wb->list_lock);
- return wrote;
+ return nr_pages - work->nr_pages;
}
/*