From mboxrd@z Thu Jan  1 00:00:00 1970
From: akpm@linux-foundation.org (Andrew Morton)
Date: Wed, 5 Sep 2018 14:57:55 -0700
Subject: [PATCH v11 0/3] remain and optimize memblock_next_valid_pfn on
 arm and arm64
In-Reply-To: <1534907237-2982-1-git-send-email-jia.he@hxt-semitech.com>
References: <1534907237-2982-1-git-send-email-jia.he@hxt-semitech.com>
Message-ID: <20180905145755.cc89819d446f311e4b8e8f95@linux-foundation.org>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, 22 Aug 2018 11:07:14 +0800 Jia He <hejianet@gmail.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?