linux-kernel - Re: RFC: mincore: add a bit to indicate a page is dirty.

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Message-ID: <87pq06f5ee.fsf@rustcorp.com.au>
Date:	Tue, 12 Feb 2013 16:19:29 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nick Piggin" <npiggin@...nel.dk>,
	Stewart Smith <stewart@...mingspork.com>
Subject: Re: RFC: mincore: add a bit to indicate a page is dirty.

Johannes Weiner <hannes@...xchg.org> writes:

> On Mon, Feb 11, 2013 at 01:43:03PM +1030, Rusty Russell wrote:
>> I am writing an app which really wants to know if a file is on the
>> disk or not (ie. do I need to sync?).
>
> When the page is under writeback, it's not necessarily on disk yet,
> but you also don't need to sync.  Which semantics make more sense?
>
> I'm leaning toward checking both PG_dirty and PG_writeback.

If it's already under PG_writeback, you probably still need to wait for
it to finish if you're trying to ensure write ordering. ie. sync.

I've updated my patch by stealing your code.

Thanks!
Rusty.
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