> > Then writeback_sb_inodes can do something like
> >
> > if (wbc.sync_mode == WB_SYNC_NONE)
> > wbc.nr_to_write = min(MAX_WRITEBACK_PAGES, work->nr_pages);
>
> I like the min() idea. However it have the side effect of (very possible)
> smallish IO from balance_dirty_pages(), which may call us with small
> ->nr_pages.
>
> We may explicitly do "write_chunk = max(MAX_WRITEBACK_PAGES, write_chunk)"
> in balance_dirty_pages() to retain the old behavior.
Sorry I was confused and please ignore the above. At least VFS won't
enlarge the writeback request from balance_dirty_pages()..
Here is the scratch patch. I'll need to double check it tomorrow, but
it's already running fine in the dd+tar+sync test and get pretty good
performance numbers.
# test-tar-dd.sh
[...]
246.62 1941.38
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 11.4383 s, 91.7 MB/s
dd if=/dev/zero of=/fs/zero bs=1M count=1000 0.00s user 2.57s system 22% cpu 11.499 total
tar jxf /dev/shm/linux-2.6.38.3.tar.bz2 12.03s user 4.36s system 56% cpu 28.770 total
286.04 2204.50
elapsed: 263.23000000000025
Thanks,
Fengguang
---
Subject: writeback: make writeback_control.nr_to_write straight
Date: Wed May 04 19:54:37 CST 2011
As suggested by Christoph:
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.
change set:
- move writeback_control from wb_writeback() down to writeback_sb_inodes()
- change return value of writeback_sb_inodes()/__writeback_inodes_wb()
to enum writeback_progress
- move MAX_WRITEBACK_PAGES and wb_writeback_work definitions to writeback.h
- add wb_writeback_work.older_than_this
- remove writeback_control.inodes_cleaned
- remove wbc_writeback_* trace events for now
CC: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
fs/fs-writeback.c | 187 +++++++++++++++---------------------
include/linux/writeback.h | 29 +++++
mm/backing-dev.c | 6 -
mm/page-writeback.c | 11 --
4 files changed, 116 insertions(+), 117 deletions(-)
--- linux-next.orig/fs/fs-writeback.c 2011-05-04 21:30:32.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2011-05-04 23:40:59.000000000 +0800
@@ -30,22 +30,6 @@
#include "internal.h"
/*
- * Passed into wb_writeback(), essentially a subset of writeback_control
- */
-struct wb_writeback_work {
- long nr_pages;
- struct super_block *sb;
- enum writeback_sync_modes sync_mode;
- unsigned int tagged_sync:1;
- unsigned int for_kupdate:1;
- unsigned int range_cyclic:1;
- unsigned int for_background:1;
-
- struct list_head list; /* pending work list */
- struct completion *done; /* set if the caller waits */
-};
-
-/*
* Include the creation of the trace points after defining the
* wb_writeback_work structure so that the definition remains local to this
* file.
@@ -463,7 +447,6 @@ writeback_single_inode(struct inode *ino
* No need to add it back to the LRU.
*/
list_del_init(&inode->i_wb_list);
- wbc->inodes_cleaned++;
}
}
inode_sync_complete(inode);
@@ -502,19 +485,53 @@ static bool pin_sb_for_writeback(struct
* 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.
*/
-static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
- struct writeback_control *wbc, bool only_this_sb)
+enum writeback_progress {
+ WROTE_FULL_CHUNK,
+ WROTE_SOME_PAGES,
+ WROTE_SOME_INODES,
+ WROTE_NOTHING,
+};
+
+static int 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_sync = work->tagged_sync,
+ .older_than_this = work->older_than_this,
+ .for_kupdate = work->for_kupdate,
+ .for_background = work->for_background,
+ .range_cyclic = work->range_cyclic,
+ .range_start = 0;
+ .range_end = LLONG_MAX;
+ };
+ long write_chunk = MAX_WRITEBACK_PAGES;
+ long wrote = 0;
+ bool inode_cleaned = false;
+
+ /*
+ * 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_sync)
+ write_chunk = LONG_MAX;
+
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
@@ -529,7 +546,7 @@ static int writeback_sb_inodes(struct su
* Bounce back to the caller to unpin this and
* pin the next superblock.
*/
- return 0;
+ break;
}
/*
@@ -543,34 +560,44 @@ static int writeback_sb_inodes(struct su
requeue_io(inode, wb);
continue;
}
-
__iget(inode);
+ write_chunk = min(write_chunk, work->nr_pages);
+ 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 (wbc.pages_skipped) {
/*
* writeback is not making progress due to locked
* buffers. Skip this inode for now.
*/
redirty_tail(inode, wb);
- }
+ } else if (!(inode->i_state & I_DIRTY))
+ inode_cleaned = true;
spin_unlock(&inode->i_lock);
spin_unlock(&wb->list_lock);
iput(inode);
cond_resched();
spin_lock(&wb->list_lock);
- if (wbc->nr_to_write <= 0)
- return 1;
+ if (wrote >= MAX_WRITEBACK_PAGES)
+ return WROTE_FULL_CHUNK;
+ if (work->nr_pages <= 0)
+ return WROTE_FULL_CHUNK;
}
- /* b_io is empty */
- return 1;
+ if (wrote)
+ return WROTE_SOME_PAGES;
+ if (inode_cleaned)
+ return WROTE_SOME_INODES;
+ return WROTE_NOTHING;
}
-static void __writeback_inodes_wb(struct bdi_writeback *wb,
- struct writeback_control *wbc)
+static int __writeback_inodes_wb(struct bdi_writeback *wb,
+ struct wb_writeback_work *work)
{
- int ret = 0;
+ int ret = WROTE_NOTHING;
while (!list_empty(&wb->b_io)) {
struct inode *inode = wb_inode(wb->b_io.prev);
@@ -580,34 +607,26 @@ static void __writeback_inodes_wb(struct
requeue_io(inode, wb);
continue;
}
- ret = writeback_sb_inodes(sb, wb, wbc, false);
+ ret = writeback_sb_inodes(sb, wb, work);
drop_super(sb);
- if (ret)
+ if (ret == WROTE_FULL_CHUNK)
break;
}
/* Leave any unwritten inodes on b_io */
+ return ret;
}
void writeback_inodes_wb(struct bdi_writeback *wb,
- struct writeback_control *wbc)
+ struct wb_writeback_work *work)
{
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, work->older_than_this);
+ __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
-
static inline bool over_bground_thresh(void)
{
unsigned long background_thresh, dirty_thresh;
@@ -636,42 +655,12 @@ static inline bool over_bground_thresh(v
static long wb_writeback(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
- struct writeback_control wbc = {
- .sync_mode = work->sync_mode,
- .tagged_sync = work->tagged_sync,
- .older_than_this = NULL,
- .for_kupdate = work->for_kupdate,
- .for_background = work->for_background,
- .range_cyclic = work->range_cyclic,
- };
- unsigned long oldest_jif;
- long wrote = 0;
- long write_chunk = MAX_WRITEBACK_PAGES;
+ long nr_pages = work->nr_pages;
+ unsigned long oldest_jif = jiffies;
struct inode *inode;
+ int progress;
- 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_sync) {
- write_chunk = LONG_MAX;
- oldest_jif = jiffies;
- wbc.older_than_this = &oldest_jif;
- }
+ work->older_than_this = &oldest_jif;
for (;;) {
/*
@@ -700,27 +689,18 @@ static long wb_writeback(struct bdi_writ
if (work->for_kupdate || work->for_background) {
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_cleaned = 0;
-
retry:
- trace_wbc_writeback_start(&wbc, wb->bdi);
spin_lock(&wb->list_lock);
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);
+ progress = __writeback_inodes_wb(wb, work);
spin_unlock(&wb->list_lock);
- trace_wbc_writeback_written(&wbc, wb->bdi);
-
- work->nr_pages -= write_chunk - wbc.nr_to_write;
- wrote += write_chunk - wbc.nr_to_write;
/*
* Did we write something? Try for more
@@ -730,9 +710,7 @@ retry:
* 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_cleaned)
+ if (progress != WROTE_NOTHING)
continue;
/*
* background writeback will start with expired inodes, and
@@ -741,10 +719,10 @@ retry:
* lists and cause trouble to the page reclaim.
*/
if (work->for_background &&
- wbc.older_than_this &&
+ work->older_than_this &&
list_empty(&wb->b_io) &&
list_empty(&wb->b_more_io)) {
- wbc.older_than_this = NULL;
+ work->older_than_this = NULL;
goto retry;
}
/*
@@ -760,7 +738,6 @@ retry:
spin_lock(&wb->list_lock);
if (!list_empty(&wb->b_more_io)) {
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);
@@ -768,7 +745,7 @@ retry:
spin_unlock(&wb->list_lock);
}
- return wrote;
+ return nr_pages - work->nr_pages;
}
/*
--- linux-next.orig/mm/backing-dev.c 2011-05-04 21:30:22.000000000 +0800
+++ linux-next/mm/backing-dev.c 2011-05-04 21:49:07.000000000 +0800
@@ -262,14 +262,14 @@ int bdi_has_dirty_io(struct backing_dev_
static void bdi_flush_io(struct backing_dev_info *bdi)
{
- struct writeback_control wbc = {
+ struct wb_writeback_work work = {
.sync_mode = WB_SYNC_NONE,
.older_than_this = NULL,
.range_cyclic = 1,
- .nr_to_write = 1024,
+ .nr_pages = 1024,
};
- writeback_inodes_wb(&bdi->wb, &wbc);
+ writeback_inodes_wb(&bdi->wb, &work);
}
/*
--- linux-next.orig/mm/page-writeback.c 2011-05-04 21:30:22.000000000 +0800
+++ linux-next/mm/page-writeback.c 2011-05-04 21:57:25.000000000 +0800
@@ -494,10 +494,10 @@ static void balance_dirty_pages(struct a
return;
for (;;) {
- struct writeback_control wbc = {
+ struct wb_writeback_work work = {
.sync_mode = WB_SYNC_NONE,
.older_than_this = NULL,
- .nr_to_write = write_chunk,
+ .nr_pages = write_chunk,
.range_cyclic = 1,
};
@@ -562,15 +562,12 @@ static void balance_dirty_pages(struct a
* threshold otherwise wait until the disk writes catch
* up.
*/
- trace_wbc_balance_dirty_start(&wbc, bdi);
if (bdi_nr_reclaimable > bdi_thresh) {
- writeback_inodes_wb(&bdi->wb, &wbc);
- pages_written += write_chunk - wbc.nr_to_write;
- trace_wbc_balance_dirty_written(&wbc, bdi);
+ writeback_inodes_wb(&bdi->wb, &work);
+ pages_written += write_chunk - work.nr_pages;
if (pages_written >= write_chunk)
break; /* We've done our duty */
}
- trace_wbc_balance_dirty_wait(&wbc, bdi);
__set_current_state(TASK_UNINTERRUPTIBLE);
io_schedule_timeout(pause);
--- linux-next.orig/include/linux/writeback.h 2011-05-04 21:30:41.000000000 +0800
+++ linux-next/include/linux/writeback.h 2011-05-04 21:43:04.000000000 +0800
@@ -7,6 +7,15 @@
#include <linux/sched.h>
#include <linux/fs.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 1024
+
struct backing_dev_info;
/*
@@ -29,7 +38,6 @@ struct writeback_control {
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_cleaned; /* # of inodes cleaned */
/*
* For a_ops->writepages(): is start or end are non-zero then this is
@@ -49,6 +57,23 @@ struct writeback_control {
};
/*
+ * Passed into wb_writeback(), essentially a subset of writeback_control
+ */
+struct wb_writeback_work {
+ long nr_pages;
+ struct super_block *sb;
+ enum writeback_sync_modes sync_mode;
+ unsigned long *older_than_this;
+ unsigned int tagged_sync:1;
+ unsigned int for_kupdate:1;
+ unsigned int range_cyclic:1;
+ unsigned int for_background:1;
+
+ struct list_head list; /* pending work list */
+ struct completion *done; /* set if the caller waits */
+};
+
+/*
* fs/fs-writeback.c
*/
struct bdi_writeback;
@@ -59,7 +84,7 @@ int writeback_inodes_sb_if_idle(struct s
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);
+ struct wb_writeback_work *work);
long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
void wakeup_flusher_threads(long nr_pages);
--
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