Subject: Re: [PATCH 0/2] Updating ctime and mtime for memory-mapped files
	[try #4]
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: salikhmetov@gmail.com, linux-mm@kvack.org, jakob@unthought.net,
       linux-kernel@vger.kernel.org, valdis.kletnieks@vt.edu, riel@redhat.com,
       ksm@42.dk, staubach@redhat.com, jesper.juhl@gmail.com,
       torvalds@linux-foundation.org, akpm@linux-foundation.org,
       protasnb@gmail.com
In-Reply-To: <E1JEsNJ-00026T-7B@pomaz-ex.szeredi.hu>
References: <12004129652397-git-send-email-salikhmetov@gmail.com>
	 <E1JEsNJ-00026T-7B@pomaz-ex.szeredi.hu>
Content-Type: text/plain
Date: Tue, 15 Jan 2008 21:32:47 +0100
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On Tue, 2008-01-15 at 21:27 +0100, Miklos Szeredi wrote:
> > 1. Introduction
> > 
> > This is the fourth version of my solution for the bug #2645:
> > 
> > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > 
> > Changes since the previous version:
> > 
> > 1) the case of retouching an already-dirty page pointed out
> >   by Miklos Szeredi has been addressed;
> 
> I'm a bit sceptical, as we've also pointed out, that this is not
> possible without messing with the page tables.
> 
> Did you try my test program on the patched kernel?
> 
> I've refreshed the patch, where we left this issue last time.  It
> should basically have equivalent functionality to your patch, and is a
> lot simpler.  There might be performance issues with it, but it's a
> good starting point.

It has the same problem as Anton's in that it won't get triggered again
for an already dirty mapped page.

But yeah, its simpler than fudging set_page_dirty().

> Index: linux/mm/memory.c
> ===================================================================
> --- linux.orig/mm/memory.c	2008-01-09 21:16:30.000000000 +0100
> +++ linux/mm/memory.c	2008-01-15 21:16:14.000000000 +0100
> @@ -1680,6 +1680,8 @@ gotten:
>  unlock:
>  	pte_unmap_unlock(page_table, ptl);
>  	if (dirty_page) {
> +		if (vma->vm_file)
> +			file_update_time(vma->vm_file);
>  		/*
>  		 * Yes, Virginia, this is actually required to prevent a race
>  		 * with clear_page_dirty_for_io() from clearing the page dirty
> @@ -2313,6 +2315,8 @@ out_unlocked:
>  	if (anon)
>  		page_cache_release(vmf.page);
>  	else if (dirty_page) {
> +		if (vma->vm_file)
> +			file_update_time(vma->vm_file);
>  		set_page_dirty_balance(dirty_page, page_mkwrite);
>  		put_page(dirty_page);
>  	}
> 

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