linux-kernel - Re: [PATCH 1/2] mm, page_alloc: don't convert pfn to idx when merging

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Date:   Fri, 9 Dec 2016 19:40:27 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>,
        Michal Hocko <mhocko@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 1/2] mm, page_alloc: don't convert pfn to idx when merging

On Fri, Dec 09, 2016 at 07:32:22PM +0100, Vlastimil Babka wrote:
> > As a slight aside, I recently spotted that one of the largest overhead
> > in the bulk free path was in the page_is_buddy() checks so pretty much
> > anything that helps that is welcome.
> 
> Interesting, the function shouldn't be doing really much on x86 without
> debug config options? We might try further optimize the zone equivalence
> checks, perhaps?

I don't have the data any more but IIRC, it was cache miss intensive and
I assumed at the time that it was checking cache cold struct pages
during merges.

At the time I was looking at splitting the per-cpu lists into irq and
non-irq so wasn't focused on the page_is_buddy part of the profile. It
just stuck in my mind as being surprisingly high.

-- 
Mel Gorman
SUSE Labs