From: Arnd Bergmann <arnd@arndb.de>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Nishanth Menon <nm@ti.com>,
Santosh Shilimkar <santosh.shilimkar@oracle.com>,
Tero Kristo <t-kristo@ti.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>,
Santosh Shilimkar <ssantosh@kernel.org>,
Dave Chinner <david@fromorbit.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Yafang Shao <laoar.shao@gmail.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Johannes Weiner <hannes@cmpxchg.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
kernel-team@fb.com, Kishon Vijay Abraham I <kishon@ti.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Roman Gushchin <guro@fb.com>
Subject: Re: [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU
Date: Wed, 11 Mar 2020 17:59:53 +0100 [thread overview]
Message-ID: <CAK8P3a2RC+sg2Tz4M8mkQ_d78FTFdES+YsucUzDFx=UK+L8Oww@mail.gmail.com> (raw)
In-Reply-To: <20200311142905.GI3216816@arrakis.emea.arm.com>
On Wed, Mar 11, 2020 at 3:29 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > - Flip TTBR0 on kernel entry/exit, and again during user access.
> >
> > This is probably more work to implement than your idea, but
> > I would hope this has a lower overhead on most microarchitectures
> > as it doesn't require pinning the pages. Depending on the
> > microarchitecture, I'd hope the overhead would be comparable
> > to that of ARM64_SW_TTBR0_PAN.
>
> This still doesn't solve the copy_{from,to}_user() case where both
> address spaces need to be available during copy. So you either pin the
> user pages in memory and access them via the kernel mapping or you
> temporarily map (kmap?) the destination/source kernel address. The
> overhead I'd expect to be significantly greater than ARM64_SW_TTBR0_PAN
> for the uaccess routines. For user entry/exit, your suggestion is
> probably comparable with SW PAN.
Good point, that is indeed a larger overhead. The simplest implementation
I had in mind would use the code from arch/arm/lib/copy_from_user.S and
flip ttbr0 between each ldm and stm (up to 32 bytes), but I have no idea
of the cost of storing to ttbr0, so this might be even more expensive. Do you
have an estimate of how long writing to TTBR0_64 takes on Cortex-A7
and A15, respectively?
Another way might be to use a use a temporary buffer that is already
mapped, and add a memcpy() through L1-cache to reduce the number
of ttbr0 changes. The buffer would probably have to be on the stack,
which limits the size, but for large copies get_user_pages()+memcpy()
may end up being faster anyway.
Arnd
next prev parent reply other threads:[~2020-03-11 17:00 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 17:55 [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU Johannes Weiner
2020-02-11 18:20 ` Johannes Weiner
2020-02-11 19:05 ` Rik van Riel
2020-02-11 19:31 ` Johannes Weiner
2020-02-11 23:44 ` Andrew Morton
2020-02-12 0:28 ` Linus Torvalds
2020-02-12 0:47 ` Andrew Morton
2020-02-12 1:03 ` Linus Torvalds
2020-02-12 8:50 ` Russell King - ARM Linux admin
2020-02-13 9:50 ` Lucas Stach
2020-02-13 16:52 ` Arnd Bergmann
2020-02-15 11:25 ` Geert Uytterhoeven
2020-02-15 16:59 ` Arnd Bergmann
2020-02-16 9:44 ` Geert Uytterhoeven
2020-02-16 19:54 ` Chris Paterson
2020-02-16 20:38 ` Arnd Bergmann
2020-02-20 14:35 ` Chris Paterson
2020-02-26 18:04 ` santosh.shilimkar
2020-02-26 21:01 ` Arnd Bergmann
2020-02-26 21:11 ` santosh.shilimkar
2020-03-06 20:34 ` Nishanth Menon
2020-03-07 1:08 ` santosh.shilimkar
2020-03-08 10:58 ` Arnd Bergmann
2020-03-08 14:19 ` Russell King - ARM Linux admin
2020-03-09 13:33 ` Arnd Bergmann
2020-03-09 14:04 ` Russell King - ARM Linux admin
2020-03-09 15:04 ` Arnd Bergmann
2020-03-10 9:16 ` Michal Hocko
2020-03-09 15:59 ` Catalin Marinas
2020-03-09 16:09 ` Russell King - ARM Linux admin
2020-03-09 16:57 ` Catalin Marinas
2020-03-09 19:46 ` Arnd Bergmann
2020-03-11 14:29 ` Catalin Marinas
2020-03-11 16:59 ` Arnd Bergmann [this message]
2020-03-11 17:26 ` Catalin Marinas
2020-03-11 22:21 ` Arnd Bergmann
2020-02-12 3:58 ` Matthew Wilcox
2020-02-12 8:09 ` Michal Hocko
2020-02-17 13:31 ` Pavel Machek
2020-02-12 16:35 ` Johannes Weiner
2020-02-12 18:26 ` Andrew Morton
2020-02-12 18:52 ` Johannes Weiner
2020-02-12 12:25 ` Yafang Shao
2020-02-12 16:42 ` Johannes Weiner
2020-02-13 1:47 ` Yafang Shao
2020-02-13 13:46 ` Johannes Weiner
2020-02-14 2:02 ` Yafang Shao
2020-02-13 18:34 ` [PATCH v2] " Johannes Weiner
2020-02-14 16:53 ` [PATCH] " kbuild test robot
2020-02-14 21:30 ` kbuild test robot
2020-02-14 21:30 ` [PATCH] vfs: fix boolreturn.cocci warnings kbuild test robot
2020-05-12 21:29 ` [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU Johannes Weiner
2020-05-13 1:32 ` Yafang Shao
2020-05-13 13:00 ` Johannes Weiner
2020-05-13 21:15 ` Andrew Morton
2020-05-14 11:27 ` Johannes Weiner
2020-05-14 2:24 ` Andrew Morton
2020-05-14 10:37 ` Johannes Weiner
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