linux-kernel - Re: [patch] mm: task dirty accounting fix

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Date:	Thu, 12 Feb 2009 02:43:58 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch] mm: task dirty accounting fix

On Tue, Feb 10, 2009 at 10:12:51AM +0100, Peter Zijlstra wrote:
> On Tue, 2009-02-10 at 05:39 +0100, Nick Piggin wrote:
> > Hi,
> > 
> > This is based from an earlier patch from YAMAMOTO-san which I have
> > somewhat simplified. What do you think?
> 
> Looks nice. Was a bit surprised we never actually merged the previous
> one though..

So was I, it was always in the back of my mind because I didn't
want to lose a good fix. I was going to just resend it, but I
decided it should actually be more consistent to do this accounting
with the other ones, and the patch ended up being much smaller as
a result too.

But credit to YAMAMOTO san for the core fix.

> 
> > Thanks,
> > Nick
> > 
> > --
> > YAMAMOTO-san noticed that task_dirty_inc doesn't seem to be called properly for
> > cases where set_page_dirty is not used to dirty a page (eg. mark_buffer_dirty).
> > 
> > Additionally, there is some inconsistency about when task_dirty_inc is
> > called. It is used for dirty balancing, however it even gets called for
> > __set_page_dirty_no_writeback.
> > 
> > So rather than increment it in a set_page_dirty wrapper, move it down to
> > exactly where the dirty page accounting stats are incremented.
> > 
> > Cc: YAMAMOTO Takashi <yamamoto@...inux.co.jp>
> > Signed-off-by: Nick Piggin <npiggin@...e.de>
> 
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> 
> > ---
> >  fs/buffer.c         |    1 +
> >  include/linux/mm.h  |    1 +
> >  mm/page-writeback.c |   13 +++----------
> >  3 files changed, 5 insertions(+), 10 deletions(-)
> > 
> > Index: linux-2.6/include/linux/mm.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/mm.h
> > +++ linux-2.6/include/linux/mm.h
> > @@ -1162,6 +1162,7 @@ extern int filemap_fault(struct vm_area_
> >  
> >  /* mm/page-writeback.c */
> >  int write_one_page(struct page *page, int wait);
> > +void task_dirty_inc(struct task_struct *tsk);
> >  
> >  /* readahead.c */
> >  #define VM_MAX_READAHEAD	128	/* kbytes */
> > Index: linux-2.6/mm/page-writeback.c
> > ===================================================================
> > --- linux-2.6.orig/mm/page-writeback.c
> > +++ linux-2.6/mm/page-writeback.c
> > @@ -241,7 +241,7 @@ void bdi_writeout_inc(struct backing_dev
> >  }
> >  EXPORT_SYMBOL_GPL(bdi_writeout_inc);
> >  
> > -static inline void task_dirty_inc(struct task_struct *tsk)
> > +void task_dirty_inc(struct task_struct *tsk)
> >  {
> >  	prop_inc_single(&vm_dirties, &tsk->dirties);
> >  }
> > @@ -1228,6 +1228,7 @@ int __set_page_dirty_nobuffers(struct pa
> >  				__inc_zone_page_state(page, NR_FILE_DIRTY);
> >  				__inc_bdi_stat(mapping->backing_dev_info,
> >  						BDI_RECLAIMABLE);
> > +				task_dirty_inc(current);
> >  				task_io_account_write(PAGE_CACHE_SIZE);
> >  			}
> >  			radix_tree_tag_set(&mapping->page_tree,
> > @@ -1263,7 +1264,7 @@ EXPORT_SYMBOL(redirty_page_for_writepage
> >   * If the mapping doesn't provide a set_page_dirty a_op, then
> >   * just fall through and assume that it wants buffer_heads.
> >   */
> > -static int __set_page_dirty(struct page *page)
> > +int set_page_dirty(struct page *page)
> >  {
> >  	struct address_space *mapping = page_mapping(page);
> >  
> > @@ -1281,14 +1282,6 @@ static int __set_page_dirty(struct page
> >  	}
> >  	return 0;
> >  }
> > -
> > -int set_page_dirty(struct page *page)
> > -{
> > -	int ret = __set_page_dirty(page);
> > -	if (ret)
> > -		task_dirty_inc(current);
> > -	return ret;
> > -}
> >  EXPORT_SYMBOL(set_page_dirty);
> >  
> >  /*
> > Index: linux-2.6/fs/buffer.c
> > ===================================================================
> > --- linux-2.6.orig/fs/buffer.c
> > +++ linux-2.6/fs/buffer.c
> > @@ -628,6 +628,7 @@ static int __set_page_dirty(struct page
> >  			__inc_zone_page_state(page, NR_FILE_DIRTY);
> >  			__inc_bdi_stat(mapping->backing_dev_info,
> >  					BDI_RECLAIMABLE);
> > +			task_dirty_inc(current);
> >  			task_io_account_write(PAGE_CACHE_SIZE);
> >  		}
> >  		radix_tree_tag_set(&mapping->page_tree,
--
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