From: Michal Hocko <mhocko@suse.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
linux-mm@kvack.org, akpm@linux-foundation.org,
kirill@shutemov.name, kirill.shutemov@linux.intel.com,
vbabka@suse.cz, will.deacon@arm.com, dave.hansen@intel.com
Subject: Re: [RFC 0/4] mm: Introduce lazy exec permission setting on a page
Date: Thu, 14 Feb 2019 09:38:44 +0100 [thread overview]
Message-ID: <20190214083844.GZ4525@dhcp22.suse.cz> (raw)
In-Reply-To: <0b6457d0-eed1-54e4-789b-d62881bea013@arm.com>
On Thu 14-02-19 11:34:09, Anshuman Khandual wrote:
>
>
> On 02/13/2019 09:08 PM, Michal Hocko wrote:
> > On Wed 13-02-19 11:21:36, Catalin Marinas wrote:
> >> On Wed, Feb 13, 2019 at 01:36:27PM +0530, Anshuman Khandual wrote:
> >>> Setting an exec permission on a page normally triggers I-cache invalidation
> >>> which might be expensive. I-cache invalidation is not mandatory on a given
> >>> page if there is no immediate exec access on it. Non-fault modification of
> >>> user page table from generic memory paths like migration can be improved if
> >>> setting of the exec permission on the page can be deferred till actual use.
> >>> There was a performance report [1] which highlighted the problem.
> >> [...]
> >>> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-December/620357.html
> >>
> >> FTR, this performance regression has been addressed by commit
> >> 132fdc379eb1 ("arm64: Do not issue IPIs for user executable ptes"). That
> >> said, I still think this patch series is valuable for further optimising
> >> the page migration path on arm64 (and can be extended to other
> >> architectures that currently require I/D cache maintenance for
> >> executable pages).
> >
> > Are there any numbers to show the optimization impact?
>
> This series transfers execution cost linearly with nr_pages from migration path
> to subsequent exec access path for normal, THP and HugeTLB pages. The experiment
> is on mainline kernel (1f947a7a011fcceb14cb912f548) along with some patches for
> HugeTLB and THP migration enablement on arm64 platform.
Please make sure that these numbers are in the changelog. I am also
missing an explanation why this is an overal win. Why should we pay
on the later access rather than the migration which is arguably a slower
path. What is the usecase that benefits from the cost shift?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-02-14 8:38 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-13 8:06 Anshuman Khandual
2019-02-13 8:06 ` [RFC 1/4] " Anshuman Khandual
2019-02-13 13:17 ` Matthew Wilcox
2019-02-13 13:53 ` Anshuman Khandual
2019-02-14 9:06 ` Mike Rapoport
2019-02-15 8:11 ` Anshuman Khandual
2019-02-15 9:49 ` Catalin Marinas
2019-02-13 8:06 ` [RFC 2/4] arm64/mm: Identify user level instruction faults Anshuman Khandual
2019-02-13 8:06 ` [RFC 3/4] arm64/mm: Allow non-exec to exec transition in ptep_set_access_flags() Anshuman Khandual
2019-02-13 8:06 ` [RFC 4/4] arm64/mm: Enable ARCH_SUPPORTS_LAZY_EXEC Anshuman Khandual
2019-02-13 11:21 ` [RFC 0/4] mm: Introduce lazy exec permission setting on a page Catalin Marinas
2019-02-13 15:38 ` Michal Hocko
2019-02-14 6:04 ` Anshuman Khandual
2019-02-14 8:38 ` Michal Hocko [this message]
2019-02-14 10:19 ` Catalin Marinas
2019-02-14 12:28 ` Michal Hocko
2019-02-15 8:45 ` Anshuman Khandual
2019-02-15 9:27 ` Michal Hocko
2019-02-18 3:07 ` Anshuman Khandual
2019-02-14 15:38 ` Dave Hansen
2019-02-18 3:19 ` Anshuman Khandual
2019-02-13 15:44 ` Dave Hansen
2019-02-14 4:12 ` Anshuman Khandual
2019-02-14 16:55 ` Dave Hansen
2019-02-18 8:31 ` Anshuman Khandual
2019-02-18 9:04 ` Catalin Marinas
2019-02-18 9:16 ` Anshuman Khandual
2019-02-18 18:20 ` Dave Hansen
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