From: Andrew Morton <akpm@linux-foundation.org>
To: Jia He <hejianet@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Michal Hocko <mhocko@suse.com>,
Wei Yang <richard.weiyang@gmail.com>,
Kees Cook <keescook@chromium.org>,
Laura Abbott <labbott@redhat.com>,
Vladimir Murzin <vladimir.murzin@arm.com>,
Philip Derrin <philip@cog.systems>,
AKASHI Takahiro <takahiro.akashi@linaro.org>,
James Morse <james.morse@arm.com>,
Steve Capper <steve.capper@arm.com>,
Pavel Tatashin <pasha.tatashin@oracle.com>,
Gioh Kim <gi-oh.kim@profitbricks.com>,
Vlastimil Babka <vbabka@suse.cz>, Mel Gorman <mgorman@suse.de>,
Johannes Weiner <hannes@cmpxchg.org>,
Kemi Wang <kemi.wang@intel.com>, Petr Tesarik <ptesarik@suse.com>,
YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Nikolay Borisov <nborisov@suse.com>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
Daniel Vacek <neelx@redhat.com>,
Eugeniu Rosca <erosca@de.adit-jv.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Jia He <jia.he@hxt-semitech.com>
Subject: Re: [RESEND PATCH v10 2/6] mm: page_alloc: remain memblock_next_valid_pfn() on arm/arm64
Date: Fri, 6 Jul 2018 15:37:09 -0700 [thread overview]
Message-ID: <20180706153709.6bcc76b0245f239f1d1dcc8a@linux-foundation.org> (raw)
In-Reply-To: <1530867675-9018-3-git-send-email-hejianet@gmail.com>
On Fri, 6 Jul 2018 17:01:11 +0800 Jia He <hejianet@gmail.com> wrote:
> From: Jia He <jia.he@hxt-semitech.com>
>
> 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.
> 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.
>
We're making a bit of a mess here. mmzone.h:
...
#ifndef CONFIG_HAVE_ARCH_PFN_VALID
...
#define next_valid_pfn(pfn) (pfn + 1)
#endif
...
#ifdef CONFIG_HAVE_MEMBLOCK_PFN_VALID
#define next_valid_pfn(pfn) memblock_next_valid_pfn(pfn)
...
#else
...
#ifndef next_valid_pfn
#define next_valid_pfn(pfn) (pfn + 1)
#endif
I guess it works OK, since CONFIG_HAVE_MEMBLOCK_PFN_VALID depends on
CONFIG_HAVE_ARCH_PFN_VALID. But it could all do with some cleanup and
modernization.
- Perhaps memblock_next_valid_pfn() should just be called
pfn_valid(). So the header file's responsibility is to provide
pfn_valid() and next_valid_pfn().
- CONFIG_HAVE_ARCH_PFN_VALID should go away. The current way of
doing such thnigs is for the arch (or some Kconfig combination) to
define pfn_valid() and next_valid_pfn() in some fashion and to then
ensure that one of them is #defined to something, to indicate that
both of these have been set up. Or something like that.
Secondly, in memmap_init_zone()
> - if (!early_pfn_valid(pfn))
> + if (!early_pfn_valid(pfn)) {
> + pfn = next_valid_pfn(pfn) - 1;
> continue;
> + }
> +
This is weird-looking. next_valid_pfn(pfn) is usually (pfn+1) so it's
a no-op. Sometimes we're calling memblock_next_valid_pfn() and then
backing up one, presumably because the `for' loop ends in `pfn++'. Or
something. Can this please be fully commented or cleaned up?
next prev parent reply other threads:[~2018-07-06 22:37 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-06 9:01 [RESEND PATCH v10 0/6] optimize memblock_next_valid_pfn and early_pfn_valid on arm and arm64 Jia He
2018-07-06 9:01 ` [RESEND PATCH v10 1/6] arm: arm64: introduce CONFIG_HAVE_MEMBLOCK_PFN_VALID Jia He
2018-08-17 14:50 ` Catalin Marinas
2018-08-20 6:27 ` Jia He
2018-07-06 9:01 ` [RESEND PATCH v10 2/6] mm: page_alloc: remain memblock_next_valid_pfn() on arm/arm64 Jia He
2018-07-06 22:37 ` Andrew Morton [this message]
2018-07-09 3:30 ` Jia He
2018-08-16 22:54 ` Pasha Tatashin
2018-07-06 9:01 ` [RESEND PATCH v10 3/6] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn() Jia He
2018-08-17 1:08 ` Pasha Tatashin
2018-08-17 1:22 ` Pasha Tatashin
2018-08-21 6:14 ` Jia He
2018-08-21 21:08 ` Andrew Morton
2018-08-22 1:38 ` Jia He
2018-07-06 9:01 ` [RESEND PATCH v10 4/6] mm/memblock: introduce memblock_search_pfn_regions() Jia He
2018-07-06 9:01 ` [RESEND PATCH v10 5/6] mm/memblock: introduce pfn_valid_region() Jia He
2018-07-06 9:01 ` [RESEND PATCH v10 6/6] mm: page_alloc: reduce unnecessary binary search in early_pfn_valid() Jia He
2018-08-17 1:35 ` Pasha Tatashin
2018-08-17 1:38 ` Pavel Tatashin
2018-08-17 5:38 ` Jia He
2018-07-06 22:41 ` [RESEND PATCH v10 0/6] optimize memblock_next_valid_pfn and early_pfn_valid on arm and arm64 Andrew Morton
2018-08-15 22:34 ` Andrew Morton
2018-08-16 19:02 ` Pasha Tatashin
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