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

[Andrea Righi]

On Tue, Feb 22, 2011 at 07:07:19PM -0500, Vivek Goyal wrote:
> On Wed, Feb 23, 2011 at 12:05:34AM +0100, Andrea Righi wrote:
> > On Tue, Feb 22, 2011 at 04:00:30PM -0500, Vivek Goyal wrote:
> > > 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?
> > 
> > Right. Probably a single one is enough:
> > 
> >  int blk_throtl_set_page_owner(struct page *page,
> > 			struct mm_struct *mm, bool anon);
> 
> Who is going to use this single export? Which module?
> 

I was actually thinking at some filesystem modules, but I was wrong,
because at the moment no one needs the export. I'll remove it in the
next version of the patch.

Thanks,
-Andrea
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