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writeback: make writeback_control.nr_to_write straight
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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>
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Wu Fengguang committed Jul 10, 2011
1 parent 36715ce commit d46db3d
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Showing 6 changed files with 148 additions and 129 deletions.
2 changes: 0 additions & 2 deletions fs/btrfs/extent_io.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2551,7 +2551,6 @@ int extent_write_full_page(struct extent_io_tree *tree, struct page *page,
};
struct writeback_control wbc_writepages = {
.sync_mode = wbc->sync_mode,
.older_than_this = NULL,
.nr_to_write = 64,
.range_start = page_offset(page) + PAGE_CACHE_SIZE,
.range_end = (loff_t)-1,
Expand Down Expand Up @@ -2584,7 +2583,6 @@ int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode,
};
struct writeback_control wbc_writepages = {
.sync_mode = mode,
.older_than_this = NULL,
.nr_to_write = nr_pages * 2,
.range_start = start,
.range_end = end + 1,
Expand Down
196 changes: 111 additions & 85 deletions fs/fs-writeback.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -29,12 +29,22 @@
#include <linux/tracepoint.h>
#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;
Expand Down Expand Up @@ -472,7 +482,6 @@ writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
* No need to add it back to the LRU.
*/
list_del_init(&inode->i_wb_list);
wbc->inodes_written++;
}
}
inode_sync_complete(inode);
Expand Down Expand Up @@ -506,25 +515,62 @@ static bool pin_sb_for_writeback(struct super_block *sb)
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.
*
* If @only_this_sb is true, then find and write all such
* 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
Expand All @@ -539,7 +585,7 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
* Bounce back to the caller to unpin this and
* pin the next superblock.
*/
return 0;
break;
}

/*
Expand All @@ -553,12 +599,18 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
requeue_io(inode, wb);
continue;
}

__iget(inode);
write_chunk = writeback_chunk_size(work);
wbc.nr_to_write = write_chunk;
wbc.pages_skipped = 0;

writeback_single_inode(inode, wb, &wbc);

pages_skipped = wbc->pages_skipped;
writeback_single_inode(inode, wb, wbc);
if (wbc->pages_skipped != pages_skipped) {
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.
Expand All @@ -570,17 +622,25 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
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);
Expand All @@ -590,33 +650,37 @@ static void __writeback_inodes_wb(struct bdi_writeback *wb,
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)
{
Expand Down Expand Up @@ -646,42 +710,13 @@ static inline bool over_bground_thresh(void)
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 (;;) {
Expand Down Expand Up @@ -711,24 +746,17 @@ static long wb_writeback(struct bdi_writeback *wb,
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
Expand All @@ -738,9 +766,7 @@ static long wb_writeback(struct bdi_writeback *wb,
* 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
Expand All @@ -753,16 +779,16 @@ static long wb_writeback(struct bdi_writeback *wb,
* 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);
}
}
spin_unlock(&wb->list_lock);

return wrote;
return nr_pages - work->nr_pages;
}

/*
Expand Down
6 changes: 1 addition & 5 deletions include/linux/writeback.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,12 +24,9 @@ enum writeback_sync_modes {
*/
struct writeback_control {
enum writeback_sync_modes sync_mode;
unsigned long *older_than_this; /* If !NULL, only write back inodes
older than this */
long nr_to_write; /* Write this many pages, and decrement
this for each page written */
long pages_skipped; /* Pages which were not written */
long inodes_written; /* # of inodes written (at least) */

/*
* For a_ops->writepages(): is start or end are non-zero then this is
Expand All @@ -56,8 +53,7 @@ void writeback_inodes_sb_nr(struct super_block *, unsigned long nr);
int writeback_inodes_sb_if_idle(struct super_block *);
int writeback_inodes_sb_nr_if_idle(struct super_block *, unsigned long nr);
void sync_inodes_sb(struct super_block *);
void writeback_inodes_wb(struct bdi_writeback *wb,
struct writeback_control *wbc);
long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages);
long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
void wakeup_flusher_threads(long nr_pages);

Expand Down
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