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SubjectRe: [PATCH 2/8] writeback: move dirty inodes from super_block to backing_dev_info
On Thu, Sep 03, 2009 at 10:46:29PM -0400, Christoph Hellwig wrote:
> On Wed, Sep 02, 2009 at 10:42:41AM +0200, Jens Axboe wrote:
> > This is a first step at introducing per-bdi flusher threads. We should
> > have no change in behaviour, although sb_has_dirty_inodes() is now
> > ridiculously expensive, as there's no easy way to answer that question.
> > Not a huge problem, since it'll be deleted in subsequent patches.
>
> After this patch generic_sync_sb_inodes becomes pretty useless. We
> have two callers which each want to call bdi_writeback_all, and one of
> them wants to wait, so just split that into a separate helper.
>
> Also move wakeup_flusher_threads into fs-writeback.c, that allows us
> to make bdi_writeback_all static.
>
> Btw, I do not think implementing sync_inodes_sb/sync_inodes_sb_wait
> is a smart and efficient idea. Right now we have a n:1 superblock:bdi
> relation, so we really should make use of that instead of doing linear
> search of all bdis in the system. If we introduce multiple bdis per
> superblock we should add an efficient lookup data structure for them.

Sorry, that patch was pre-fixing and quilt refresh. Proper one below:


Index: linux-2.6/fs/fs-writeback.c
===================================================================
--- linux-2.6.orig/fs/fs-writeback.c 2009-09-03 23:35:30.544832785 -0300
+++ linux-2.6/fs/fs-writeback.c 2009-09-03 23:48:32.596833183 -0300
@@ -836,7 +836,7 @@ int bdi_writeback_task(struct bdi_writeb
* we are simply called for WB_SYNC_NONE, then writeback will merely be
* scheduled to run.
*/
-void bdi_writeback_all(struct writeback_control *wbc)
+static void bdi_writeback_all(struct writeback_control *wbc)
{
const bool must_wait = wbc->sync_mode == WB_SYNC_ALL;
struct backing_dev_info *bdi;
@@ -894,6 +894,25 @@ restart:
}
}

+/*
+ * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
+ * the whole world.
+ */
+void wakeup_flusher_threads(long nr_pages)
+{
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ .older_than_this = NULL,
+ .range_cyclic = 1,
+ };
+
+ if (nr_pages == 0)
+ nr_pages = global_page_state(NR_FILE_DIRTY) +
+ global_page_state(NR_UNSTABLE_NFS);
+ wbc.nr_to_write = nr_pages;
+ bdi_writeback_all(&wbc);
+}
+
static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
@@ -1012,81 +1031,53 @@ out:
EXPORT_SYMBOL(__mark_inode_dirty);

/*
- * Write out a superblock's list of dirty inodes. A wait will be performed
- * upon no inodes, all inodes or the final one, depending upon sync_mode.
- *
- * If older_than_this is non-NULL, then only write out inodes which
- * had their first dirtying at a time earlier than *older_than_this.
- *
- * If we're a pdlfush thread, then implement pdflush collision avoidance
- * against the entire list.
- *
- * If `bdi' is non-zero then we're being asked to writeback a specific queue.
- * This function assumes that the blockdev superblock's inodes are backed by
- * a variety of queues, so all inodes are searched. For other superblocks,
- * assume that all inodes are backed by the same queue.
- *
- * The inodes to be written are parked on bdi->b_io. They are moved back onto
- * bdi->b_dirty as they are selected for writing. This way, none can be missed
- * on the writer throttling path, and we get decent balancing between many
- * throttled threads: we don't want them all piling up on inode_sync_wait.
+ * For a data integrity sync we must wait for all pages under writeback,
+ * because there may have been pages dirtied before our sync call, but which
+ * had writeout started before we write it out. In which case, the inode
+ * may not be on the dirty list, but we still have to wait for that writeout.
*/
-static void generic_sync_sb_inodes(struct writeback_control *wbc)
+static void wait_sb_inodes(struct writeback_control *wbc)
{
- if (wbc->bdi)
- bdi_start_writeback(wbc);
- else
- bdi_writeback_all(wbc);
+ struct inode *inode, *old_inode = NULL;

- if (wbc->sync_mode == WB_SYNC_ALL) {
- struct inode *inode, *old_inode = NULL;
+ /*
+ * We need to be protected against the filesystem going from
+ * r/o to r/w or vice versa.
+ */
+ WARN_ON(!rwsem_is_locked(&wbc->sb->s_umount));

- /*
- * We need to be protected against the filesystem going from
- * r/o to r/w or vice versa.
- */
- WARN_ON(!rwsem_is_locked(&wbc->sb->s_umount));
+ spin_lock(&inode_lock);

- spin_lock(&inode_lock);
+ list_for_each_entry(inode, &wbc->sb->s_inodes, i_sb_list) {
+ struct address_space *mapping;
+
+ if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
+ continue;
+ mapping = inode->i_mapping;
+ if (mapping->nrpages == 0)
+ continue;
+ __iget(inode);
+ spin_unlock(&inode_lock);

/*
- * Data integrity sync. Must wait for all pages under writeback,
- * because there may have been pages dirtied before our sync
- * call, but which had writeout started before we write it out.
- * In which case, the inode may not be on the dirty list, but
- * we still have to wait for that writeout.
+ * We hold a reference to 'inode' so it couldn't have
+ * been removed from s_inodes list while we dropped the
+ * inode_lock. We cannot iput the inode now as we can
+ * be holding the last reference and we cannot iput it
+ * under inode_lock. So we keep the reference and iput
+ * it later.
*/
- list_for_each_entry(inode, &wbc->sb->s_inodes, i_sb_list) {
- struct address_space *mapping;
-
- if (inode->i_state &
- (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
- continue;
- mapping = inode->i_mapping;
- if (mapping->nrpages == 0)
- continue;
- __iget(inode);
- spin_unlock(&inode_lock);
- /*
- * We hold a reference to 'inode' so it couldn't have
- * been removed from s_inodes list while we dropped the
- * inode_lock. We cannot iput the inode now as we can
- * be holding the last reference and we cannot iput it
- * under inode_lock. So we keep the reference and iput
- * it later.
- */
- iput(old_inode);
- old_inode = inode;
+ iput(old_inode);
+ old_inode = inode;

- filemap_fdatawait(mapping);
+ filemap_fdatawait(mapping);

- cond_resched();
+ cond_resched();

- spin_lock(&inode_lock);
- }
- spin_unlock(&inode_lock);
- iput(old_inode);
+ spin_lock(&inode_lock);
}
+ spin_unlock(&inode_lock);
+ iput(old_inode);
}

/**
@@ -1112,7 +1103,7 @@ long sync_inodes_sb(struct super_block *
(inodes_stat.nr_inodes - inodes_stat.nr_unused);

wbc.nr_to_write = nr_to_write;
- generic_sync_sb_inodes(&wbc);
+ bdi_writeback_all(&wbc);
return nr_to_write - wbc.nr_to_write;
}
EXPORT_SYMBOL(sync_inodes_sb);
@@ -1132,10 +1123,11 @@ long sync_inodes_sb_wait(struct super_bl
.range_start = 0,
.range_end = LLONG_MAX,
};
- long nr_to_write = LLONG_MAX; /* doesn't actually matter */
+ long nr_to_write = LONG_MAX; /* doesn't actually matter */

wbc.nr_to_write = nr_to_write;
- generic_sync_sb_inodes(&wbc);
+ bdi_writeback_all(&wbc);
+ wait_sb_inodes(&wbc);
return nr_to_write - wbc.nr_to_write;
}
EXPORT_SYMBOL(sync_inodes_sb_wait);
Index: linux-2.6/include/linux/backing-dev.h
===================================================================
--- linux-2.6.orig/include/linux/backing-dev.h 2009-09-03 23:42:42.968834087 -0300
+++ linux-2.6/include/linux/backing-dev.h 2009-09-03 23:42:45.124832763 -0300
@@ -99,7 +99,6 @@ int bdi_register_dev(struct backing_dev_
void bdi_unregister(struct backing_dev_info *bdi);
void bdi_start_writeback(struct writeback_control *wbc);
int bdi_writeback_task(struct bdi_writeback *wb);
-void bdi_writeback_all(struct writeback_control *wbc);
int bdi_has_dirty_io(struct backing_dev_info *bdi);

extern spinlock_t bdi_lock;
Index: linux-2.6/include/linux/writeback.h
===================================================================
--- linux-2.6.orig/include/linux/writeback.h 2009-09-03 23:42:11.956834796 -0300
+++ linux-2.6/include/linux/writeback.h 2009-09-03 23:42:32.708832476 -0300
@@ -85,6 +85,7 @@ long sync_inodes_sb(struct super_block *
long sync_inodes_sb_wait(struct super_block *);
void sync_inodes_wbc(struct writeback_control *wbc);
long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
+void wakeup_flusher_threads(long nr_pages);

/* writeback.h requires fs.h; it, too, is not included from here. */
static inline void wait_on_inode(struct inode *inode)
@@ -104,7 +105,6 @@ static inline void inode_sync_wait(struc
/*
* mm/page-writeback.c
*/
-void wakeup_flusher_threads(long nr_pages);
void laptop_io_completion(void);
void laptop_sync_completion(void);
void throttle_vm_writeout(gfp_t gfp_mask);
Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c 2009-09-03 23:41:42.724833252 -0300
+++ linux-2.6/mm/page-writeback.c 2009-09-03 23:41:51.368832827 -0300
@@ -674,25 +674,6 @@ void throttle_vm_writeout(gfp_t gfp_mask
}
}

-/*
- * Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
- * the whole world.
- */
-void wakeup_flusher_threads(long nr_pages)
-{
- struct writeback_control wbc = {
- .sync_mode = WB_SYNC_NONE,
- .older_than_this = NULL,
- .range_cyclic = 1,
- };
-
- if (nr_pages == 0)
- nr_pages = global_page_state(NR_FILE_DIRTY) +
- global_page_state(NR_UNSTABLE_NFS);
- wbc.nr_to_write = nr_pages;
- bdi_writeback_all(&wbc);
-}
-
static void laptop_timer_fn(unsigned long unused);

static DEFINE_TIMER(laptop_mode_wb_timer, laptop_timer_fn, 0, 0);

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