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Date: Wed, 23 May 2012 10:24:35 -0700 From: Tejun Heo <tj@...nel.org> To: Kent Overstreet <koverstreet@...gle.com> Cc: linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org, dm-devel@...hat.com, agk@...hat.com Subject: Re: [Bcache v13 11/16] bcache: Core btree code Hello, On Wed, May 23, 2012 at 01:34:03AM -0400, Kent Overstreet wrote: > On Tue, May 22, 2012 at 10:20:54PM -0700, Tejun Heo wrote: > > Hmmm... I would prefer it to be defined explicitly as union. It's > > rather easy to define it incorrectly (ie. using struct bkey) and then > > pass it around expecting it to have the pad. > > Thing is, things don't expect the pad - bkeys are normally just in a big > chunk of memory concatenated together, and the same functions have to > work both with those and with bare bkeys the code occasionally > manipulates. Hmmm... so it's actually just padding? Padding for what? I thought it was there to provide space for ptr[], no? > > I'm a bit confused. Cache device or cached device? Isn't the key > > dev:offset:size of the cached device? > > No - bkey->key is the offset on the cached device, PTR_OFFSET is on the > cache. > > Confusing, I know. Any ideas for better terminology? Double confused by the "no" and the following sentence seemingly agreeing with what I wrote. So, bkey->key indexes the backend device - the slow big disk and the associated PTRs point into the fast SSD caching device, right? If so, I think 'key' is fine, that's the only thing which can be key anyway. As for PTR_XXX, maybe something which can signify they're the cache would be nicer but with proper comments I don't think it's big deal. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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