Date: Mon, 31 Jan 2005 13:01:04 -0800
From: Andrew Morton <akpm@osdl.org>
To: linux-kernel@vger.kernel.org
Cc: timur.tabi@ammasso.com, roland@topspin.com
Subject: Re: Correct way to release get_user_pages()?
Message-Id: <20050131130104.4ac732e5.akpm@osdl.org>
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Timur Tabi <timur.tabi@ammasso.com> wrote:
>
> Andrew Morton wrote:
> 
> > no...  You should only dirty the page if it was modified, and then use
> > set_page_dirty() or set_page_dirty_lock().
> 
> If the page was modified, then shouldn't it already be marked dirty?

If the page is modified by a DMA transfer or by the CPU via the kernel's
page mappings then there is no record of its having been altered.  Which is
why we must do it in software.

> Also, should I always use set_page_dirty_lock() if I haven't already 
> locked the page?

If you don't have a reference on the page's inode, yes, you should use
set_page_dirty_lock().  If the page came from get_user_pages() then surely
you don't have a ref on the inode.
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