linux-kernel - Re: [RESEND PATCH v10 6/6] mm: page_alloc: reduce unnecessary binary search in early_pfn

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Date:   Fri, 17 Aug 2018 01:35:22 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     Jia He <hejianet@...il.com>, Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>
CC:     Wei Yang <richard.weiyang@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Philip Derrin <philip@....systems>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        James Morse <james.morse@....com>,
        Steve Capper <steve.capper@....com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Gioh Kim <gi-oh.kim@...fitbricks.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Kemi Wang <kemi.wang@...el.com>,
        Petr Tesarik <ptesarik@...e.com>,
        YASUAKI ISHIMATSU <yasu.isimatu@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Nikolay Borisov <nborisov@...e.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Daniel Vacek <neelx@...hat.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Jia He <jia.he@...-semitech.com>
Subject: Re: [RESEND PATCH v10 6/6] mm: page_alloc: reduce unnecessary binary
 search in early_pfn_valid()



On 7/6/18 5:01 AM, Jia He wrote:
> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> where possible") optimized the loop in memmap_init_zone(). But there is
> still some room for improvement. E.g. in early_pfn_valid(), if pfn and
> pfn+1 are in the same memblock region, we can record the last returned
> memblock region index and check whether pfn++ is still in the same
> region.
> 
> Currently it only improve the performance on arm/arm64 and will have no
> impact on other arches.
> 
> For the performance improvement, after this set, I can see the time
> overhead of memmap_init() is reduced from 27956us to 13537us in my
> armv8a server(QDF2400 with 96G memory, pagesize 64k).

This series would be a lot simpler if patches 4, 5, and 6 were dropped.
The extra complexity does not make sense to save 0.0001s/T during not.

Patches 1-3, look OK, but without patches 4-5 __init_memblock should be
made local static as I suggested earlier.

So, I think Jia should re-spin this series with only 3 patches. Or,
Andrew could remove the from linux-next before merge.

Thank you,
Pavel