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Date: Wed, 23 Jan 2002 12:55:28 -0800
From: Andrew Morton <akpm@zip.com.au>
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To: "Stephen C. Tweedie" <sct@redhat.com>
CC: Rik van Riel <riel@conectiva.com.br>, Hans Reiser <reiser@namesys.com>,
        Andreas Dilger <adilger@turbolabs.com>, Chris Mason <mason@suse.com>,
        Shawn Starr <spstarr@sh0n.net>, linux-kernel@vger.kernel.org,
        ext2-devel@lists.sourceforge.net
Subject: Re: [Ext2-devel] Re: Possible Idea with filesystem buffering.
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		<Pine.LNX.4.33L.0201221649430.32617-100000@imladris.surriel.com>; from riel@conectiva.com.br on Tue, Jan 22, 2002 at 05:03:02PM -0200 <20020123203500.L1930@redhat.com>
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"Stephen C. Tweedie" wrote:
> 
> Hi,
> 
> On Tue, Jan 22, 2002 at 05:03:02PM -0200, Rik van Riel wrote:
> > On Tue, 22 Jan 2002, Andrew Morton wrote:
> > > Hans Reiser wrote:
> > >
> > > Note that writepage() doesn't get used much.  Most VM-initiated
> > > filesystem writeback activity is via try_to_release_page(), which
> > > has somewhat more vague and flexible semantics.
> >
> > We may want to change this though, or at the very least get
> > rid of the horrible interplay between ->writepage and
> > try_to_release_page() ...
> 
> This is actually really important --- writepage on its own cannot
> distinguish between requests to flush something to disk (eg. msync or
> fsync), and requests to evict dirty data from memory.
> 
> This is really important for ext3's data journaling mode --- syncing
> to disk only requires flushing as far as the journal, but evicting
> dirty pages requires a full writeback too.  That's one place where our
> traditional VM notion of writepage just isn't quite fine-grained
> enough.

And we use currently use PF_MEMALLOC to work out which context
we're being called from.  Sigh.

I wish I'd taken better notes of all the square pegs which
ext3 had to push into the kernel's round holes.  But there
were so many :)

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