linux-kernel - Re: [PATCH][RFC][BUG] updating the ctime and mtime time stamps in msync()

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Date:	Wed, 09 Jan 2008 16:06:17 -0500
From:	Valdis.Kletnieks@...edu
To:	Rik van Riel <riel@...hat.com>
Cc:	Anton Salikhmetov <salikhmetov@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC][BUG] updating the ctime and mtime time stamps in msync()

On Wed, 09 Jan 2008 15:50:15 EST, Rik van Riel said:

> Could you explain (using short words and simple sentences) what the
> exact problem is?
> 
> Eg.
> 
> 1) program mmaps file
> 2) program writes to mmaped area
> 3) ???                   <=== this part, in equally simple words :)
> 4) data loss

It's like this:

Monday  9:04AM:  System boots, database server starts up, mmaps file
Monday  9:06AM:  Database server writes to mmap area, updates mtime/ctime
Monday <many times> Database server writes to mmap area, no further update..
Monday 11:45PM:  Backup sees "file modified 9:06AM, let's back it up"
Tuesday 9:00AM-5:00PM: Database server touches it another 5,398 times, no mtime
Tuesday 11:45PM: Backup sees "file modified back on Monday, we backed this up..
Wed  9:00AM-5:00PM: More updates, more not touching the mtime
Wed  11:45PM: *yawn* It hasn't been touched in 2 days, no sense in backing it up..

Lather, rinse, repeat....

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