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Message-Id: <20180815153456.974798c62dd5a5e4628db8f5@linux-foundation.org>
Date: Wed, 15 Aug 2018 15:34:56 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Jia He <hejianet@...il.com>
Cc: 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>,
Michal Hocko <mhocko@...e.com>,
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-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [RESEND PATCH v10 0/6] optimize memblock_next_valid_pfn and
early_pfn_valid on arm and arm64
On Fri, 6 Jul 2018 17:01:09 +0800 Jia He <hejianet@...il.com> wrote:
> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> where possible") optimized the loop in memmap_init_zone(). But it causes
> possible panic bug. So Daniel Vacek reverted it later.
>
> But as suggested by Daniel Vacek, it is fine to using memblock to skip
> gaps and finding next valid frame with CONFIG_HAVE_ARCH_PFN_VALID.
>
> More from what Daniel said:
> "On arm and arm64, memblock is used by default. But generic version of
> pfn_valid() is based on mem sections and memblock_next_valid_pfn() does
> not always return the next valid one but skips more resulting in some
> valid frames to be skipped (as if they were invalid). And that's why
> kernel was eventually crashing on some !arm machines."
>
> About the performance consideration:
> As said by James in b92df1de5,
> "I have tested this patch on a virtual model of a Samurai CPU with a
> sparse memory map. The kernel boot time drops from 109 to 62 seconds."
> Thus it would be better if we remain memblock_next_valid_pfn on arm/arm64.
>
> Besides we can remain memblock_next_valid_pfn, there is still some room
> for 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). I believe arm server will benefit more if memory is
> larger than TBs
This patchset is basically unreviewed at this stage. Could people
please find some time to check it carefully?
Thanks.
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