[Devel] Re: [PATCH 4/5] blk-throttle: track buffered and anonymous pages

[Vivek Goyal]

On Tue, Feb 22, 2011 at 06:12:55PM +0100, Andrea Righi wrote:
> Add the tracking of buffered (writeback) and anonymous pages.
> 
> Dirty pages in the page cache can be processed asynchronously by the
> per-bdi flusher kernel threads or by any other thread in the system,
> according to the writeback policy.
> 
> For this reason the real writes to the underlying block devices may
> occur in a different IO context respect to the task that originally
> generated the dirty pages involved in the IO operation. This makes
> the tracking and throttling of writeback IO more complicate respect to
> the synchronous IO from the blkio controller's point of view.
> 
> The idea is to save the cgroup owner of each anonymous page and dirty
> page in page cache. A page is associated to a cgroup the first time it
> is dirtied in memory (for file cache pages) or when it is set as
> swap-backed (for anonymous pages). This information is stored using the
> page_cgroup functionality.
> 
> Then, at the block layer, it is possible to retrieve the throttle group
> looking at the bio_page(bio). If the page was not explicitly associated
> to any cgroup the IO operation is charged to the current task/cgroup, as
> it was done by the previous implementation.
> 
> Signed-off-by: Andrea Righi <arighi at develer.com>
> ---
>  block/blk-throttle.c   |   87 +++++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/blkdev.h |   26 ++++++++++++++-
>  2 files changed, 111 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 9ad3d1e..a50ee04 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -8,6 +8,10 @@
>  #include <linux/slab.h>
>  #include <linux/blkdev.h>
>  #include <linux/bio.h>
> +#include <linux/memcontrol.h>
> +#include <linux/mm_inline.h>
> +#include <linux/pagemap.h>
> +#include <linux/page_cgroup.h>
>  #include <linux/blktrace_api.h>
>  #include <linux/blk-cgroup.h>
>  
> @@ -221,6 +225,85 @@ done:
>  	return tg;
>  }
>  
> +static inline bool is_kernel_io(void)
> +{
> +	return !!(current->flags & (PF_KTHREAD | PF_KSWAPD | PF_MEMALLOC));
> +}
> +
> +static int throtl_set_page_owner(struct page *page, struct mm_struct *mm)
> +{
> +	struct blkio_cgroup *blkcg;
> +	unsigned short id = 0;
> +
> +	if (blkio_cgroup_disabled())
> +		return 0;
> +	if (!mm)
> +		goto out;
> +	rcu_read_lock();
> +	blkcg = task_to_blkio_cgroup(rcu_dereference(mm->owner));
> +	if (likely(blkcg))
> +		id = css_id(&blkcg->css);
> +	rcu_read_unlock();
> +out:
> +	return page_cgroup_set_owner(page, id);
> +}
> +
> +int blk_throtl_set_anonpage_owner(struct page *page, struct mm_struct *mm)
> +{
> +	return throtl_set_page_owner(page, mm);
> +}
> +EXPORT_SYMBOL(blk_throtl_set_anonpage_owner);
> +
> +int blk_throtl_set_filepage_owner(struct page *page, struct mm_struct *mm)
> +{
> +	if (is_kernel_io() || !page_is_file_cache(page))
> +		return 0;
> +	return throtl_set_page_owner(page, mm);
> +}
> +EXPORT_SYMBOL(blk_throtl_set_filepage_owner);

Why are we exporting all these symbols?

Thanks
Vivek
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