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From: Catalin Marinas <catalin.marinas@arm.com>
To: Steve Capper <steve.capper@linaro.org>
Cc: "linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux@arm.linux.org.uk" <linux@arm.linux.org.uk>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"gary.robertson@linaro.org" <gary.robertson@linaro.org>,
	"anders.roxell@linaro.org" <anders.roxell@linaro.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH V4 6/7] arm64: mm: Enable HAVE_RCU_TABLE_FREE logic
Date: Wed, 30 Apr 2014 16:20:47 +0100	[thread overview]
Message-ID: <20140430152047.GF31220@arm.com> (raw)
In-Reply-To: <1396018892-6773-7-git-send-email-steve.capper@linaro.org>

On Fri, Mar 28, 2014 at 03:01:31PM +0000, Steve Capper wrote:
> In order to implement fast_get_user_pages we need to ensure that the
> page table walker is protected from page table pages being freed from
> under it.
> 
> This patch enables HAVE_RCU_TABLE_FREE, any page table pages belonging
> to address spaces with multiple users will be call_rcu_sched freed.
> Meaning that disabling interrupts will block the free and protect the
> fast gup page walker.
> 
> Signed-off-by: Steve Capper <steve.capper@linaro.org>

While this patch is simple, I'd like to better understand the reason for
it. Currently HAVE_RCU_TABLE_FREE is enabled for powerpc and sparc while
__get_user_pages_fast() is supported by a few other architectures that
don't select HAVE_RCU_TABLE_FREE. So why do we need it for fast gup on
arm/arm64 while not all the other archs need it?

Thanks.

-- 
Catalin

WARNING: multiple messages have this Message-ID (diff)
From: catalin.marinas@arm.com (Catalin Marinas)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC PATCH V4 6/7] arm64: mm: Enable HAVE_RCU_TABLE_FREE logic
Date: Wed, 30 Apr 2014 16:20:47 +0100	[thread overview]
Message-ID: <20140430152047.GF31220@arm.com> (raw)
In-Reply-To: <1396018892-6773-7-git-send-email-steve.capper@linaro.org>

On Fri, Mar 28, 2014 at 03:01:31PM +0000, Steve Capper wrote:
> In order to implement fast_get_user_pages we need to ensure that the
> page table walker is protected from page table pages being freed from
> under it.
> 
> This patch enables HAVE_RCU_TABLE_FREE, any page table pages belonging
> to address spaces with multiple users will be call_rcu_sched freed.
> Meaning that disabling interrupts will block the free and protect the
> fast gup page walker.
> 
> Signed-off-by: Steve Capper <steve.capper@linaro.org>

While this patch is simple, I'd like to better understand the reason for
it. Currently HAVE_RCU_TABLE_FREE is enabled for powerpc and sparc while
__get_user_pages_fast() is supported by a few other architectures that
don't select HAVE_RCU_TABLE_FREE. So why do we need it for fast gup on
arm/arm64 while not all the other archs need it?

Thanks.

-- 
Catalin

WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Steve Capper <steve.capper@linaro.org>
Cc: "linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux@arm.linux.org.uk" <linux@arm.linux.org.uk>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"gary.robertson@linaro.org" <gary.robertson@linaro.org>,
	"anders.roxell@linaro.org" <anders.roxell@linaro.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH V4 6/7] arm64: mm: Enable HAVE_RCU_TABLE_FREE logic
Date: Wed, 30 Apr 2014 16:20:47 +0100	[thread overview]
Message-ID: <20140430152047.GF31220@arm.com> (raw)
In-Reply-To: <1396018892-6773-7-git-send-email-steve.capper@linaro.org>

On Fri, Mar 28, 2014 at 03:01:31PM +0000, Steve Capper wrote:
> In order to implement fast_get_user_pages we need to ensure that the
> page table walker is protected from page table pages being freed from
> under it.
> 
> This patch enables HAVE_RCU_TABLE_FREE, any page table pages belonging
> to address spaces with multiple users will be call_rcu_sched freed.
> Meaning that disabling interrupts will block the free and protect the
> fast gup page walker.
> 
> Signed-off-by: Steve Capper <steve.capper@linaro.org>

While this patch is simple, I'd like to better understand the reason for
it. Currently HAVE_RCU_TABLE_FREE is enabled for powerpc and sparc while
__get_user_pages_fast() is supported by a few other architectures that
don't select HAVE_RCU_TABLE_FREE. So why do we need it for fast gup on
arm/arm64 while not all the other archs need it?

Thanks.

-- 
Catalin

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  reply	other threads:[~2014-04-30 15:21 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-03-28 15:01 [RFC PATCH V4 0/7] get_user_pages_fast for ARM and ARM64 Steve Capper
2014-03-28 15:01 ` Steve Capper
2014-03-28 15:01 ` Steve Capper
2014-03-28 15:01 ` [RFC PATCH V4 1/7] mm: Introduce a general RCU get_user_pages_fast Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01 ` [RFC PATCH V4 2/7] arm: mm: Introduce special ptes for LPAE Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01 ` [RFC PATCH V4 3/7] arm: mm: Enable HAVE_RCU_TABLE_FREE logic Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-05-01 11:11   ` Catalin Marinas
2014-05-01 11:11     ` Catalin Marinas
2014-05-01 11:11     ` Catalin Marinas
2014-05-01 11:44     ` Steve Capper
2014-05-01 11:44       ` Steve Capper
2014-05-01 11:44       ` Steve Capper
2014-03-28 15:01 ` [RFC PATCH V4 4/7] arm: mm: Enable RCU fast_gup Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01 ` [RFC PATCH V4 5/7] arm64: Convert asm/tlb.h to generic mmu_gather Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01 ` [RFC PATCH V4 6/7] arm64: mm: Enable HAVE_RCU_TABLE_FREE logic Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-04-30 15:20   ` Catalin Marinas [this message]
2014-04-30 15:20     ` Catalin Marinas
2014-04-30 15:20     ` Catalin Marinas
2014-04-30 15:33     ` Catalin Marinas
2014-04-30 15:33       ` Catalin Marinas
2014-04-30 15:33       ` Catalin Marinas
2014-04-30 15:38       ` Steve Capper
2014-04-30 15:38         ` Steve Capper
2014-04-30 15:38         ` Steve Capper
2014-04-30 17:21         ` Catalin Marinas
2014-04-30 17:21           ` Catalin Marinas
2014-04-30 17:21           ` Catalin Marinas
2014-05-01  7:34           ` Steve Capper
2014-05-01  7:34             ` Steve Capper
2014-05-01  7:34             ` Steve Capper
2014-05-01  9:52             ` Catalin Marinas
2014-05-01  9:52               ` Catalin Marinas
2014-05-01  9:52               ` Catalin Marinas
2014-05-01  9:57               ` Peter Zijlstra
2014-05-01  9:57                 ` Peter Zijlstra
2014-05-01  9:57                 ` Peter Zijlstra
2014-05-01 10:04                 ` Catalin Marinas
2014-05-01 10:04                   ` Catalin Marinas
2014-05-01 10:04                   ` Catalin Marinas
2014-05-01 10:15                   ` Steve Capper
2014-05-01 10:15                     ` Steve Capper
2014-05-01 10:15                     ` Steve Capper
2014-03-28 15:01 ` [RFC PATCH V4 7/7] arm64: mm: Enable RCU fast_gup Steve Capper
2014-03-28 15:01   ` Steve Capper
2014-03-28 15:01   ` Steve Capper

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