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

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Date:	Fri, 18 Jan 2008 12:36:08 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	a.p.zijlstra@...llo.nl
CC:	miklos@...redi.hu, 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,
	torvalds@...ux-foundation.org, 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

> Possibly, I didn't see a quick way to break that iteration.
> >From a quick glance at prio_tree.c the iterator isn't valid anymore
> after releasing i_mmap_lock. Fixing that would be,.. 'fun'.

Maybe i_mmap_lock isn't needed at all, since msync holds mmap_sem,
which protects the prio tree as well, no?

> I also realized I forgot to copy/paste the prio_tree_iter declaration
> and ought to make all these functions static.
> 
> But for a quick draft it conveys the idea pretty well, I guess :-)

Yes :)

There could also be nasty performance corner cases, like having a huge
file mapped thousands of times, and having only a couple of pages
dirtied between MS_ASYNC invocations.  Then most of that page table
walking would be just unnecessary overhead.

There's something to be said for walking only the dirty pages, and
doing page_mkclean on them, even if in some cases that would be
slower.

But I have a strong feeling of deja vu, and last time it ended with
Andrew not liking the whole thing...

Miklos
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