linux-kernel - RE: [PATCH V8 4/8] mm/fs: add hooks to support cleancache

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Message-ID: <36009196-0fe9-43f2-8d16-4cc58232195f@default>
Date:	Fri, 15 Apr 2011 08:32:21 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Chris Mason <chris.mason@...cle.com>, viro@...iv.linux.org.uk,
	adilger.kernel@...ger.ca, tytso@....edu, mfasheh@...e.com,
	jlbec@...lplan.org, matthew@....cx, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org, ocfs2-devel@....oracle.com,
	linux-mm@...ck.org, hch@...radead.org, ngupta@...are.org,
	jeremy@...p.org, JBeulich@...ell.com,
	Kurt Hackel <kurt.hackel@...cle.com>, npiggin@...nel.dk,
	Dave Mccracken <dave.mccracken@...cle.com>, riel@...hat.com,
	avi@...hat.com, Konrad Wilk <konrad.wilk@...cle.com>,
	mel@....ul.ie, yinghan@...gle.com, gthelen@...gle.com,
	torvalds@...ux-foundation.org
Subject: RE: [PATCH V8 4/8] mm/fs: add hooks to support cleancache

> From: Andrew Morton [mailto:akpm@...ux-foundation.org]
> On Fri, 15 Apr 2011 07:47:57 -0700 (PDT) Dan Magenheimer
> <dan.magenheimer@...cle.com> wrote:
> 
> > Hi Minchan --
> >
> > > Before I suggested a thing about cleancache_flush_page,
> > > cleancache_flush_inode.
> > >
> > > what's the meaning of flush's semantic?
> > > I thought it means invalidation.
> > > AFAIC, how about change flush with invalidate?
> >
> > I'm not sure the words "flush" and "invalidate" are defined
> > precisely or used consistently everywhere in computer
> > science, but I think that "invalidate" is to destroy
> > a "pointer" to some data, but not necessarily destroy the
> > data itself.   And "flush" means to actually remove
> > the data.  So one would "invalidate a mapping" but one
> > would "flush a cache".
> >
> > Since cleancache_flush_page and cleancache_flush_inode
> > semantically remove data from cleancache, I think flush
> > is a better name than invalidate.
> >
> > Does that make sense?
> 
> nope ;)
> 
> Kernel code freely uses "flush" to refer to both invalidation and to
> writeback, sometimes in confusing ways.  In this case,
> cleancache_flush_inode and cleancache_flush_page rather sound like they
> might write those things to backing store.

OK, I guess I am displaying my kernel-newbie-ness... though,
in this case, writeback of a cleancache page to backing store
doesn't make much sense either (since cleancache pages are
by definition "clean").

I'm happy to rename the hooks, though will probably not
repost a V9 unless/until more substantive changes collect...
unless someone considers this an unmergeable offense.

Thanks for the feedback, Minchan and Andrew!
Dan
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