linux-ext4 - Re: [PATCH V8 4/8] mm/fs: add hooks to support cleancache

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Message-Id: <20110415081054.79a164d3.akpm@linux-foundation.org>
Date:	Fri, 15 Apr 2011 08:10:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
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

On Fri, 15 Apr 2011 07:47:57 -0700 (PDT) Dan Magenheimer <dan.magenheimer@...cle.com> wrote:

> Hi Minchan --
> 
> > First of all, thanks for resolving conflict with my patch.
> 
> You're welcome!  As I pointed out offlist, yours was the first
> change in MM that caused any semantic changes to the cleancache
> core hooks patch since before 2.6.18.
>  
> > 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.  
--
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