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

[OGAWA Hirofumi]

Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
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