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

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Message-ID: <871v135xvj.fsf@devron.myhome.or.jp>
Date:	Sat, 16 Apr 2011 00:37:36 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	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

Andrew Morton <akpm@...ux-foundation.org> writes:

>> > 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.  

I'd like to mention about *_{get,put}_page too. In linux get/put is not
meaning read/write. There is {get,put}_page those are refcount stuff
(Yeah, and I felt those methods does refcount by quick read. But it
seems to be false. There is no xen codes, so I don't know actually
though.).

And I agree, I also think the needing thing is consistency on the linux
codes (term).

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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