linux-kernel - Re: [PATCH -v6 2/2] Updating ctime and mtime for memory-mapped files

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Date:	Fri, 18 Jan 2008 20:22:32 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	torvalds@...ux-foundation.org
CC:	miklos@...redi.hu, peterz@...radead.org, salikhmetov@...il.com,
	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, akpm@...ux-foundation.org,
	protasnb@...il.com, r.e.wolff@...wizard.nl,
	hidave.darkstar@...il.com, hch@...radead.org
Subject: Re: [PATCH -v6 2/2] Updating ctime and mtime for memory-mapped
 files

> > 
> > But then background writeout, sync(2), etc, wouldn't update the times.
> 
> Sure it would, but only when doing the final unmap.
> 
> Did you miss the "on unmap and msync" part?

No :)

What I'm saying is that the times could be left un-updated for a long
time if program doesn't do munmap() or msync(MS_SYNC) for a long time.

If program has this pattern:

mmap()
write to map
msync(MS_ASYNC)
sleep(long)
write to map
msync(MS_ASYNC)
sleep(long)
...

Then we'd never see time updates (until the program exits, but that
could be years).

Maybe this doesn't matter, I'm just saying this is a disadvantage
compared to the "update on first dirtying" approach, which would
ensure, that times are updated at least once per 30s.

Miklos
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