From: Daniel Jordan <daniel.m.jordan@oracle.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Prathu Baronia <prathu.baronia@oneplus.com>,
alexander.duyck@gmail.com, chintan.pandya@oneplus.com,
ying.huang@intel.com, akpm@linux-foundation.com,
linux-mm@kvack.org, gregkh@linuxfoundation.com,
gthelen@google.com, jack@suse.cz, ken.lin@oneplus.com,
gasine.xu@oneplus.com
Subject: Re: [PATCH v2] mm: Optimized hugepage zeroing & copying from user
Date: Tue, 14 Apr 2020 13:41:20 -0400 [thread overview]
Message-ID: <20200414174120.pufhdh3i5thro6pq@ca-dmjordan1.us.oracle.com> (raw)
In-Reply-To: <20200414170312.GR4629@dhcp22.suse.cz>
On Tue, Apr 14, 2020 at 07:03:12PM +0200, Michal Hocko wrote:
> On Tue 14-04-20 21:08:32, Prathu Baronia wrote:
> > In !HIGHMEM cases, specially in 64-bit architectures, we don't need temp mapping
> > of pages. Hence, k(map|unmap)_atomic() acts as nothing more than multiple
> > barrier() calls, for example for a 2MB hugepage in clear_huge_page() these are
> > called 512 times i.e. to map and unmap each subpage that means in total 2048
> > barrier calls.
I think barrier() only matters at compile time.
> > This called for optimization. Simply getting VADDR from page does
> > the job for us. This also applies to the copy_user_huge_page() function.
>
> I still have hard time to see why kmap machinery should introduce any
> slowdown here. Previous data posted while discussing v1 didn't really
> show anything outside of the noise.
Maybe pagefault_disable/enable are barely showing up. Alternatively, do you
have CONFIG_PREEMPT_COUNT enabled?
next prev parent reply other threads:[~2020-04-14 17:41 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 15:38 [PATCH v2] mm: Optimized hugepage zeroing & copying from user Prathu Baronia
2020-04-14 17:03 ` Michal Hocko
2020-04-14 17:41 ` Daniel Jordan [this message]
[not found] ` <20200414184743.GB2097@oneplus.com>
2020-04-14 19:32 ` Alexander Duyck
2020-04-15 3:40 ` Huang, Ying
2020-04-15 11:09 ` Michal Hocko
2020-04-19 12:05 ` Prathu Baronia
2020-04-14 19:40 ` Michal Hocko
2020-04-15 3:27 ` Huang, Ying
2020-04-16 1:21 ` Huang, Ying
2020-04-19 15:58 ` Prathu Baronia
2020-04-20 0:18 ` Huang, Ying
2020-04-21 9:36 ` Prathu Baronia
2020-04-21 10:09 ` Will Deacon
2020-04-21 12:47 ` Vlastimil Babka
2020-04-21 12:48 ` Vlastimil Babka
2020-04-21 13:39 ` Will Deacon
2020-04-21 13:48 ` Vlastimil Babka
2020-04-21 13:56 ` Chintan Pandya
2020-04-22 8:18 ` Will Deacon
2020-04-22 11:19 ` Will Deacon
2020-04-22 14:38 ` Prathu Baronia
2020-05-01 8:58 ` Prathu Baronia
2020-05-05 8:59 ` Will Deacon
2020-04-21 13:00 ` Michal Hocko
2020-04-21 13:10 ` Will Deacon
2020-04-17 7:48 ` [mm] 134c8b410f: vm-scalability.median -7.9% regression kernel test robot
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