From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jann Horn <jannh@google.com>
Cc: kernel test robot <rong.a.chen@intel.com>,
Christoph Hellwig <hch@lst.de>, Oleg Nesterov <oleg@redhat.com>,
Kirill Shutemov <kirill@shutemov.name>, Jan Kara <jack@suse.cz>,
Andrea Arcangeli <aarcange@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org
Subject: Re: [gup] 17839856fd: stress-ng.vm-splice.ops_per_sec 2158.6% improvement
Date: Mon, 15 Jun 2020 12:09:58 -0700 [thread overview]
Message-ID: <CAHk-=wgAH-yXX=1T_hqenVVmQPVKP-dkRKKkHYcWAXK0tRzz6Q@mail.gmail.com> (raw)
In-Reply-To: <CAG48ez1v1b4X5LgFya6nvi33-TWwqna_dc5jGFVosqQhdn_Nkg@mail.gmail.com>
On Mon, Jun 15, 2020 at 12:33 AM Jann Horn <jannh@google.com> wrote:
>
> So in summary I guess the test was just really slow up until now
> because it was hitting a slowpath that you wouldn't hit during normal
> usage? At least for vmsplice(), writing uninitialized pages doesn't
> really make a whole lot of sense...
Heh. My main worry with that commit was that we'd see the reverse
effect: somebody implicitly depending on the continued sharing of
pages in some odd splice situation, and where breaking the COW would
result in a performance degradation.
The fact that it went the other way instead is somewhat ironic.
But good.
I guess I'll just ping the stable people to say "yeah, put that in
stable too". It's a fix, and apparently it _helps_ performance for the
degenerate cases rather than hurting anything.
Linus
prev parent reply other threads:[~2020-06-15 19:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-11 4:04 [gup] 17839856fd: stress-ng.vm-splice.ops_per_sec 2158.6% improvement kernel test robot
2020-06-11 20:24 ` Linus Torvalds
2020-06-12 0:07 ` [LKP] " Philip Li
2020-06-15 6:58 ` Feng Tang
2020-06-15 7:32 ` Jann Horn
2020-06-15 8:33 ` [LKP] " Feng Tang
2020-06-15 19:09 ` Linus Torvalds [this message]
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