From: Linus Torvalds <torvalds@linux-foundation.org>
To: Will Deacon <will@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Vinayak Menon <vinmenon@codeaurora.org>,
Hugh Dickins <hughd@google.com>,
Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag
Date: Fri, 8 Jan 2021 11:42:39 -0800 [thread overview]
Message-ID: <CAHk-=wh=6=7qYKL0RLbzg4vKnT0v_c66n8RYS-CvmUxnO9MxPw@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wg3UkUdiTbqWFx3zBLXv9VJHuNZAa5QyDvXiSmD4gX94A@mail.gmail.com>
On Fri, Jan 8, 2021 at 11:34 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Yeah, I think that's a side effect of "now the code really makes a lot
> more sense". Your subsequent patches 2-3 certainly are much simpler
> now
On that note - they could be simpler still if this was just done
entirely unconditionally..
I'm taking your word for "it makes sense", but when you say
On CPUs with hardware AF/DBM, initialising prefaulted PTEs as 'old'
improves vmscan behaviour and does not appear to introduce any overhead.
in the description for patch 3, it makes me wonder how noticeable the
overhead is on the hardware that _does_ take a fault on old pte's..
IOW, it would be lovely to see numbers if you have any like that..
Both ways, actually. Because I also wonder how noticeable the vmscan
improvement is. You say there's no measurable overhead for platforms
with hardware dirty/accessed bits, but maybe there's not a lot of
measurable improvements from a more exact accessed bit either?
Linus
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Will Deacon <will@kernel.org>
Cc: Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Hugh Dickins <hughd@google.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Vinayak Menon <vinmenon@codeaurora.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Android Kernel Team <kernel-team@android.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag
Date: Fri, 8 Jan 2021 11:42:39 -0800 [thread overview]
Message-ID: <CAHk-=wh=6=7qYKL0RLbzg4vKnT0v_c66n8RYS-CvmUxnO9MxPw@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wg3UkUdiTbqWFx3zBLXv9VJHuNZAa5QyDvXiSmD4gX94A@mail.gmail.com>
On Fri, Jan 8, 2021 at 11:34 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Yeah, I think that's a side effect of "now the code really makes a lot
> more sense". Your subsequent patches 2-3 certainly are much simpler
> now
On that note - they could be simpler still if this was just done
entirely unconditionally..
I'm taking your word for "it makes sense", but when you say
On CPUs with hardware AF/DBM, initialising prefaulted PTEs as 'old'
improves vmscan behaviour and does not appear to introduce any overhead.
in the description for patch 3, it makes me wonder how noticeable the
overhead is on the hardware that _does_ take a fault on old pte's..
IOW, it would be lovely to see numbers if you have any like that..
Both ways, actually. Because I also wonder how noticeable the vmscan
improvement is. You say there's no measurable overhead for platforms
with hardware dirty/accessed bits, but maybe there's not a lot of
measurable improvements from a more exact accessed bit either?
Linus
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-01-08 19:43 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 17:15 [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Will Deacon
2021-01-08 17:15 ` Will Deacon
2021-01-08 17:15 ` [PATCH v2 1/3] mm: Cleanup faultaround and finish_fault() codepaths Will Deacon
2021-01-08 17:15 ` Will Deacon
2021-01-11 14:26 ` Kirill A. Shutemov
2021-01-11 14:26 ` Kirill A. Shutemov
2021-01-11 14:27 ` Will Deacon
2021-01-11 14:27 ` Will Deacon
2021-01-08 17:15 ` [PATCH v2 2/3] mm: Allow architectures to request 'old' entries when prefaulting Will Deacon
2021-01-08 17:15 ` Will Deacon
2021-01-11 14:25 ` Kirill A. Shutemov
2021-01-11 14:25 ` Kirill A. Shutemov
2021-01-11 14:37 ` Will Deacon
2021-01-11 14:37 ` Will Deacon
2021-01-11 14:47 ` Kirill A. Shutemov
2021-01-11 14:47 ` Kirill A. Shutemov
2021-01-08 17:15 ` [PATCH v2 3/3] arm64: mm: Implement arch_wants_old_prefaulted_pte() Will Deacon
2021-01-08 17:15 ` Will Deacon
2021-01-08 19:34 ` [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Linus Torvalds
2021-01-08 19:34 ` Linus Torvalds
2021-01-08 19:34 ` Linus Torvalds
2021-01-08 19:42 ` Linus Torvalds [this message]
2021-01-08 19:42 ` Linus Torvalds
2021-01-08 19:42 ` Linus Torvalds
2021-01-11 14:01 ` Will Deacon
2021-01-11 14:01 ` Will Deacon
2021-01-11 13:30 ` Will Deacon
2021-01-11 13:30 ` Will Deacon
2021-01-11 21:03 ` Hugh Dickins
2021-01-11 21:03 ` Hugh Dickins
2021-01-11 21:03 ` Hugh Dickins
2021-01-12 21:46 ` Will Deacon
2021-01-12 21:46 ` Will Deacon
2021-01-11 14:24 ` Kirill A. Shutemov
2021-01-11 14:24 ` Kirill A. Shutemov
2021-01-11 19:25 ` Linus Torvalds
2021-01-11 19:25 ` Linus Torvalds
2021-01-11 19:25 ` Linus Torvalds
2021-01-12 21:47 ` Will Deacon
2021-01-12 21:47 ` Will Deacon
2021-01-12 21:55 ` Linus Torvalds
2021-01-12 21:55 ` Linus Torvalds
2021-01-12 21:55 ` Linus Torvalds
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