All of lore.kernel.org
 help / color / mirror / Atom feed
From: Catalin Marinas <catalin.marinas@arm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Jianyong Wu <Jianyong.Wu@arm.com>,
	Anshuman Khandual <Anshuman.Khandual@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"ardb@kernel.org" <ardb@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	 "gshan@redhat.com" <gshan@redhat.com>,
	Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping
Date: Mon, 13 Dec 2021 09:57:08 +0000	[thread overview]
Message-ID: <YbcY9Kjd2ZzDxOZu@arm.com> (raw)
In-Reply-To: <3366ba9f-5993-1c52-de0c-53e618f20cd8@redhat.com>

On Mon, Dec 13, 2021 at 08:37:04AM +0100, David Hildenbrand wrote:
> On 13.12.21 08:27, Jianyong Wu wrote:
> >>> @@ -359,6 +365,7 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
> >>>  	} while (pudp++, addr = next, addr != end);
> >>>
> >>>  	pud_clear_fixmap();
> >>> +	spin_unlock(&fixmap_lock);
> >>>  }
> >>>
> >>>  static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
> >>>
> >>
> >> As the race could only happen with memory hotplug being enabled, could
> >> not we wrap this around with CONFIG_MEMORY_HOTPLUG, just to narrow
> >> its scope possibly speed up other non-hotplug cases ?

Assuming you can quantify the speed-up...

> > I think it's better.
> 
> We better avoid using ifdef if not really necessary, it just uglifies
> the code. We could add
> 
> if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> 	...
> 
> But should we really try to micto-optimize this code and make it harder
> to read for the purpose of an unproven performance gain? (if there is no
> contention, we'll most probably not even recognize that we're taking a lock)

I agree, I don't see the point of this optimisation.

-- 
Catalin

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Jianyong Wu <Jianyong.Wu@arm.com>,
	Anshuman Khandual <Anshuman.Khandual@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"ardb@kernel.org" <ardb@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"gshan@redhat.com" <gshan@redhat.com>,
	Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping
Date: Mon, 13 Dec 2021 09:57:08 +0000	[thread overview]
Message-ID: <YbcY9Kjd2ZzDxOZu@arm.com> (raw)
In-Reply-To: <3366ba9f-5993-1c52-de0c-53e618f20cd8@redhat.com>

On Mon, Dec 13, 2021 at 08:37:04AM +0100, David Hildenbrand wrote:
> On 13.12.21 08:27, Jianyong Wu wrote:
> >>> @@ -359,6 +365,7 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
> >>>  	} while (pudp++, addr = next, addr != end);
> >>>
> >>>  	pud_clear_fixmap();
> >>> +	spin_unlock(&fixmap_lock);
> >>>  }
> >>>
> >>>  static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
> >>>
> >>
> >> As the race could only happen with memory hotplug being enabled, could
> >> not we wrap this around with CONFIG_MEMORY_HOTPLUG, just to narrow
> >> its scope possibly speed up other non-hotplug cases ?

Assuming you can quantify the speed-up...

> > I think it's better.
> 
> We better avoid using ifdef if not really necessary, it just uglifies
> the code. We could add
> 
> if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> 	...
> 
> But should we really try to micto-optimize this code and make it harder
> to read for the purpose of an unproven performance gain? (if there is no
> contention, we'll most probably not even recognize that we're taking a lock)

I agree, I don't see the point of this optimisation.

-- 
Catalin

  reply	other threads:[~2021-12-13 10:17 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-10  9:54 [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping Jianyong Wu
2021-12-10  9:54 ` Jianyong Wu
2021-12-10 11:22 ` Catalin Marinas
2021-12-10 11:22   ` Catalin Marinas
2021-12-13  5:24   ` Jianyong Wu
2021-12-13  5:24     ` Jianyong Wu
2021-12-13  6:56 ` Anshuman Khandual
2021-12-13  6:56   ` Anshuman Khandual
2021-12-13  7:27   ` Jianyong Wu
2021-12-13  7:27     ` Jianyong Wu
2021-12-13  7:37     ` David Hildenbrand
2021-12-13  7:37       ` David Hildenbrand
2021-12-13  9:57       ` Catalin Marinas [this message]
2021-12-13  9:57         ` Catalin Marinas
2021-12-13 10:16 ` Anshuman Khandual
2021-12-13 10:16   ` Anshuman Khandual
2021-12-13 10:35   ` Ard Biesheuvel
2021-12-13 10:35     ` Ard Biesheuvel
2021-12-13 13:45     ` Will Deacon
2021-12-13 13:45       ` Will Deacon
2021-12-13 14:01       ` Ard Biesheuvel
2021-12-13 14:01         ` Ard Biesheuvel
2021-12-13 16:42 ` Will Deacon
2021-12-13 16:42   ` Will Deacon
2021-12-15 14:13 ` Qian Cai
2021-12-15 14:13   ` Qian Cai
2021-12-15 16:02   ` Catalin Marinas
2021-12-15 16:02     ` Catalin Marinas
2021-12-15 16:04     ` David Hildenbrand
2021-12-15 16:04       ` David Hildenbrand
2021-12-16  3:00       ` Jianyong Wu
2021-12-16  3:00         ` Jianyong Wu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YbcY9Kjd2ZzDxOZu@arm.com \
    --to=catalin.marinas@arm.com \
    --cc=Anshuman.Khandual@arm.com \
    --cc=Jianyong.Wu@arm.com \
    --cc=Justin.He@arm.com \
    --cc=akpm@linux-foundation.org \
    --cc=ardb@kernel.org \
    --cc=david@redhat.com \
    --cc=gshan@redhat.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=nd@arm.com \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.