linux-kernel - Re: [PATCH 0/2] Updating ctime and mtime for memory-mapped files [try #4]

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Message-Id: <E1JEsNJ-00026T-7B@pomaz-ex.szeredi.hu>
Date:	Tue, 15 Jan 2008 21:27:09 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	salikhmetov@...il.com
CC:	linux-mm@...ck.org, jakob@...hought.net,
	linux-kernel@...r.kernel.org, valdis.kletnieks@...edu,
	riel@...hat.com, ksm@...dk, staubach@...hat.com,
	jesper.juhl@...il.com, torvalds@...ux-foundation.org,
	a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
	protasnb@...il.com, miklos@...redi.hu
Subject: Re: [PATCH 0/2] Updating ctime and mtime for memory-mapped files [try #4]

> 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.

Miklos
----

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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