linux-kernel - Re: [PATCH] mm/hugetlb: remove unnecessary memory fetch in PageHeadHuge()

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Message-ID: <20200312004252.efb3bfirdk4ghe4z@black.fi.intel.com>
Date:   Thu, 12 Mar 2020 03:42:52 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: remove unnecessary memory fetch in
 PageHeadHuge()

On Thu, Mar 12, 2020 at 03:41:19AM +0300, Kirill A. Shutemov wrote:
> On Wed, Mar 11, 2020 at 06:24:40PM +0100, Vlastimil Babka wrote:
> > Commit f1e61557f023 ("mm: pack compound_dtor and compound_order into one word
> > in struct page") changed compound_dtor from a pointer to an array index in
> > order to pack it. To check if page has the hugeltbfs compound_dtor, we can
> > just compare the index directly without fetching the function pointer.
> > Said commit did that with PageHuge() and we can do the same with PageHeadHuge()
> > to make the code a bit smaller and faster.
> > 
> > Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> > Cc: Mike Kravetz <mike.kravetz@...cle.com>
> > Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> 
> We use literaly the same check in the function next to this one --
> PageHuge().

Ugh.. I have to read the commit message, not only the code :P

-- 
 Kirill A. Shutemov