linux-kernel - Re: Bloat caused by unnecessary calls to compound

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Message-ID: <20160401013329.GB1323@zzz>
Date:	Thu, 31 Mar 2016 20:33:29 -0500
From:	Eric Biggers <ebiggers3@...il.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kirill.shutemov@...ux.intel.com, Hugh Dickins <hughd@...gle.com>
Subject: Re: Bloat caused by unnecessary calls to compound_head()?

On Sun, Mar 27, 2016 at 10:46:49PM +0300, Kirill A. Shutemov wrote:
> The idea is to introduce new type to indicate head page --
> 'struct head_page' -- it's compatible with struct page on memory layout,
> but distinct from C point of view. compound_head() should return pointer
> of that type. For the proof-of-concept I've introduced new helper --
> compound_head_t().
> 

Well, it's good for optimizing the specific case of mark_page_accessed().  I'm
more worried about the general level of bloat, since the Page* macros are used
in so many places.  And generating page-flags.h with a script is something to be
avoided if at all possible.

I wasn't following the discussion around the original page-flags patchset.  Can
you point me to a discussion of the benefits of the page "policy" checks --- why
are they suddenly needed when they weren't before?  Or any helpful comments in
the code?