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Date: Tue, 17 Feb 2009 16:38:20 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Edward Shishkin <edward.shishkin@gmail.com>
Cc: peterz@infradead.org, npiggin@suse.de, rmh3093@gmail.com,
       randy.dunlap@oracle.com, linux-kernel@vger.kernel.org,
       reiserfs-devel@vger.kernel.org
Subject: Re: [patch 2/4] vfs: add set_page_dirty_notag
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On Wed, 18 Feb 2009 03:26:16 +0300
Edward Shishkin <edward.shishkin@gmail.com> wrote:

> Andrew Morton wrote:
> > On Tue, 17 Feb 2009 01:43:28 +0300
> > Edward Shishkin <edward.shishkin@gmail.com> wrote:
> >
> >   
> >> + */
> >> +int set_page_dirty_notag(struct page *page)
> >> +{
> >> +	struct address_space *mapping = page->mapping;
> >> +
> >> +	if (!TestSetPageDirty(page)) {
> >> +		WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
> >> +		if (mapping_cap_account_dirty(mapping)) {
> >> +		        /*
> >> +			 * The accounting functions rely on
> >> +			 * being atomic wrt interrupts.
> >> +			 */
> >> +		        unsigned long flags;
> >> +			local_irq_save(flags);
> >> +			__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);
> >> +			local_irq_restore(flags);
> >> +		}
> >> +		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> >> +		return 1;
> >> +	}
> >> +	return 0;
> >> +}
> >>     
> >
> > I'll maintain this in -mm, alongside the resier4 patches which need it.
> >
> > Of course, this rather obviates the purpose - if someone changes, say,
> > __set_page_dirty_nobuffers() then they won't similarly update
> > set_page_dirty_notag().  Oh well.
> >
> > This problem would fix itself if those two functions were to
> > substantially share code.
> 
> It will fix the problem only partially:
> there is one more friend __set_page_dirty() in buffer.c

But all three functions do the same thing?

			if (mapping_cap_account_dirty(mapping)) {
				__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);
			}

?

> Maybe it makes sense to add comments with warnings
> in all such places, or create a header file with a static inline
> function update_page_accounting() ?

Could just uninline the helper function I guess - if you look, those
four statements already involve doing a heck of a lot of stuff.

Try it, see how it looks?