linux-kernel - Re: [PATCH -v8 3/4] Enable the MS_ASYNC functionality in sys

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Message-Id: <E1JHlh8-0003s8-Bb@pomaz-ex.szeredi.hu>
Date:	Wed, 23 Jan 2008 20:55:34 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	torvalds@...ux-foundation.org
CC:	a.p.zijlstra@...llo.nl, 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, miklos@...redi.hu,
	r.e.wolff@...wizard.nl, hidave.darkstar@...il.com,
	hch@...radead.org
Subject: Re: [PATCH -v8 3/4] Enable the MS_ASYNC functionality in
 sys_msync()

> > 
> > It would need some addition piece to not call msync_interval() for
> > MS_SYNC, and remove the balance_dirty_pages_ratelimited_nr() stuff.
> > 
> > But yeah, this pte walker is much better. 
> 
> Actually, I think this patch is much better. 
> 
> Anyway, it's better because:
>  - it actually honors the range
>  - it uses the same code for MS_ASYNC and MS_SYNC
>  - it just avoids doing the "wait for" for MS_ASYNC.
> 
> However, it's totally untested, of course. What did you expect? Clean code 
> _and_ testing? 
> 
> [ Side note: it is quite possible that we should not do the 
>   SYNC_FILE_RANGE_WAIT_BEFORE on MS_ASYNC, and just skip over pages that 
>   are busily under writeback already.

MS_ASYNC is not supposed to wait, so SYNC_FILE_RANGE_WAIT_BEFORE
probably should not be used in that case.

What would be perfect, is if we had a sync mode, that on encountering
a page currently under writeback, would just do a page_mkclean() on
it, so we still receive a page fault next time one of the mappings is
dirtied, so the times can be updated.

Would there be any difficulties with that?

Miklos
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