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Date: Thu, 6 Sep 2018 11:47:07 +0100 From: Will Deacon <will.deacon@....com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Jia He <hejianet@...il.com>, Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....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>, 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, Jia He <jia.he@...-semitech.com> Subject: Re: [PATCH v11 0/3] remain and optimize memblock_next_valid_pfn on arm and arm64 On Wed, Sep 05, 2018 at 02:57:55PM -0700, Andrew Morton wrote: > On Wed, 22 Aug 2018 11:07:14 +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 > > Thanks. I switched to v11. It would be nice to see some confirmation > from ARM people please? I'll take a look... Will
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