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SubjectRe: [PATCH 8/8] blk-throttle: enable throttling of task while dirtying pages
On Tue, Jun 28, 2011 at 11:35:09AM -0400, Vivek Goyal wrote:
> Put the blk_throtl_dirty_pages() hook in
> balance_dirty_pages_ratelimited_nr() to enable task throttling.
>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---
> include/linux/blkdev.h | 5 +++++
> mm/page-writeback.c | 3 +++
> 2 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 4ce6e68..5d4a57e 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1180,12 +1180,17 @@ static inline uint64_t rq_io_start_time_ns(struct request *req)
> extern int blk_throtl_init(struct request_queue *q);
> extern void blk_throtl_exit(struct request_queue *q);
> extern int blk_throtl_bio(struct request_queue *q, struct bio **bio);
> +extern void blk_throtl_dirty_pages(struct address_space *mapping,
> + unsigned long nr_dirty);
> #else /* CONFIG_BLK_DEV_THROTTLING */
> static inline int blk_throtl_bio(struct request_queue *q, struct bio **bio)
> {
> return 0;
> }
>
> +static inline void blk_throtl_dirty_pages(struct address_space *mapping,
> + unsigned long nr_dirty) {}
> +
> static inline int blk_throtl_init(struct request_queue *q) { return 0; }
> static inline int blk_throtl_exit(struct request_queue *q) { return 0; }
> #endif /* CONFIG_BLK_DEV_THROTTLING */
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 31f6988..943e551 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -629,6 +629,9 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
> unsigned long ratelimit;
> unsigned long *p;
>
> + /* Subject writes to IO controller throttling */
> + blk_throtl_dirty_pages(mapping, nr_pages_dirtied);
> +

mmmh.. in this way we throttle also tasks that are re-writing dirty pages
multiple times.

From the controller perspective what is actually generating I/O on block
devices is the generation of _new_ dirty pages. Multiple re-writes in page
cache should never be throttled IMHO.

I would re-write this patch in the following way. What do you think?

Thanks,
-Andrea

---
Subject: [PATCH 8/8] blk-throttle: enable throttling of task while dirtying pages
From: Andrea Righi <andrea@betterlinux.com>

Put the blk_throtl_dirty_pages() hook in balance_dirty_pages_ratelimited_nr()
to enable task throttling.

Moreover, modify balance_dirty_pages_ratelimited_nr() to accept the additional
parameter "redirty". This parameter can be used to notify if the pages have
been dirtied for the first time or re-dirtied.

This information can be used by the blkio.throttle controller to distinguish
between a WRITE in the page cache, that will eventually generates I/O activity
on block device by the writeback code, and a re-WRITE operation that most of
the time will not generate additional I/O activity.

This means that a task that re-writes multiple times the same blocks of a file
is affected by the blkio limitations only for the actual I/O that will be
performed to the underlying block devices during the writeback process.

Signed-off-by: Andrea Righi <andrea@betterlinux.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
include/linux/writeback.h | 8 ++++++--
mm/filemap.c | 4 +++-
mm/page-writeback.c | 11 +++++++----
3 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 17e7ccc..82d69c9 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -129,8 +129,12 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,
unsigned long dirty);

void page_writeback_init(void);
-void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
- unsigned long nr_pages_dirtied);
+
+#define balance_dirty_pages_ratelimited_nr(__mapping, __nr) \
+ __balance_dirty_pages_ratelimited_nr(__mapping, __nr, false)
+void __balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
+ unsigned long nr_pages_dirtied,
+ bool redirty);

static inline void
balance_dirty_pages_ratelimited(struct address_space *mapping)
diff --git a/mm/filemap.c b/mm/filemap.c
index a8251a8..ff4bdc5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2377,6 +2377,7 @@ static ssize_t generic_perform_write(struct file *file,
unsigned long bytes; /* Bytes to write to page */
size_t copied; /* Bytes copied from user */
void *fsdata;
+ unsigned int dirty;

offset = (pos & (PAGE_CACHE_SIZE - 1));
bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
@@ -2412,6 +2413,7 @@ again:
pagefault_enable();
flush_dcache_page(page);

+ dirty = PageDirty(page);
mark_page_accessed(page);
status = a_ops->write_end(file, mapping, pos, bytes, copied,
page, fsdata);
@@ -2438,7 +2440,7 @@ again:
pos += copied;
written += copied;

- balance_dirty_pages_ratelimited(mapping);
+ __balance_dirty_pages_ratelimited_nr(mapping, 1, dirty);

} while (iov_iter_count(i));

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 943e551..4ca505d 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -613,6 +613,7 @@ static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
* balance_dirty_pages_ratelimited_nr - balance dirty memory state
* @mapping: address_space which was dirtied
* @nr_pages_dirtied: number of pages which the caller has just dirtied
+ * @redirty: false if the pages have been dirtied for the first time
*
* Processes which are dirtying memory should call in here once for each page
* which was newly dirtied. The function will periodically check the system's
@@ -623,14 +624,16 @@ static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
* limit we decrease the ratelimiting by a lot, to prevent individual processes
* from overshooting the limit by (ratelimit_pages) each.
*/
-void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
- unsigned long nr_pages_dirtied)
+void __balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
+ unsigned long nr_pages_dirtied,
+ bool redirty)
{
unsigned long ratelimit;
unsigned long *p;

/* Subject writes to IO controller throttling */
- blk_throtl_dirty_pages(mapping, nr_pages_dirtied);
+ if (!redirty)
+ blk_throtl_dirty_pages(mapping, nr_pages_dirtied);

ratelimit = ratelimit_pages;
if (mapping->backing_dev_info->dirty_exceeded)
@@ -652,7 +655,7 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
}
preempt_enable();
}
-EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
+EXPORT_SYMBOL(__balance_dirty_pages_ratelimited_nr);

void throttle_vm_writeout(gfp_t gfp_mask)
{

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