linux-kernel - Re: RFC: mincore: add a bit to indicate a page is dirty.

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Message-Id: <20130211141239.f4decf03.akpm@linux-foundation.org>
Date:	Mon, 11 Feb 2013 14:12:39 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Stewart Smith <stewart@...mingspork.com>
Subject: Re: RFC: mincore: add a bit to indicate a page is dirty.

On Mon, 11 Feb 2013 11:27:01 -0500
Johannes Weiner <hannes@...xchg.org> wrote:

> > Is PG_dirty the right choice?  Is that right for huge pages?  Should I
> > assume is_migration_entry(entry) means it's not dirty, or is there some
> > other check here?
> 
> If your only consequence of finding dirty pages is to sync, would you
> be better off using fsync/fdatasync maybe?

Yes, if the data is all on disk then an fsync() will be a no-op.  IOW,

	if (I need to fsync)
		fsync();

is equivalent to

	fsync();


Methinks we need to understand the requirement better.


Also, having to mmap the file to be able to query pagecache state is a
hack.  Whatever happened to the fincore() patch?

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