From: Michal Hocko <mhocko@kernel.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: linux-kernel@vger.kernel.org, Robin Murphy <robin.murphy@arm.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>,
Brendan Gregg <bgregg@netflix.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Christian Hansen <chansen3@cisco.com>,
dancol@google.com, fmayer@google.com,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
kernel-team@android.com, linux-api@vger.kernel.org,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Mike Rapoport <rppt@linux.ibm.com>,
minchan@kernel.org, namhyung@google.com, paulmck@linux.ibm.com,
Roman Gushchin <guro@fb.com>,
Stephen Rothwell <sfr@canb.auug.org.au>,
surenb@google.com, Thomas Gleixner <tglx@linutronix.de>,
tkjos@google.com, Vladimir Davydov <vdavydov.dev@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.org>
Subject: Re: [PATCH v4 3/5] [RFC] arm64: Add support for idle bit in swap PTE
Date: Tue, 6 Aug 2019 12:47:55 +0200 [thread overview]
Message-ID: <20190806104755.GR11812@dhcp22.suse.cz> (raw)
In-Reply-To: <20190806103627.GA218260@google.com>
On Tue 06-08-19 06:36:27, Joel Fernandes wrote:
> On Tue, Aug 06, 2019 at 10:42:03AM +0200, Michal Hocko wrote:
> > On Mon 05-08-19 13:04:49, Joel Fernandes (Google) wrote:
> > > This bit will be used by idle page tracking code to correctly identify
> > > if a page that was swapped out was idle before it got swapped out.
> > > Without this PTE bit, we lose information about if a page is idle or not
> > > since the page frame gets unmapped.
> >
> > And why do we need that? Why cannot we simply assume all swapped out
> > pages to be idle? They were certainly idle enough to be reclaimed,
> > right? Or what does idle actualy mean here?
>
> Yes, but other than swapping, in Android a page can be forced to be swapped
> out as well using the new hints that Minchan is adding?
Yes and that is effectivelly making them idle, no?
> Also, even if they were idle enough to be swapped, there is a chance that they
> were marked as idle and *accessed* before the swapping. Due to swapping, the
> "page was accessed since we last marked it as idle" information is lost. I am
> able to verify this.
>
> Idle in this context means the same thing as in page idle tracking terms, the
> page was not accessed by userspace since we last marked it as idle (using
> /proc/<pid>/page_idle).
Please describe a usecase and why that information might be useful.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-08-06 10:48 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-05 17:04 [PATCH v4 1/5] mm/page_idle: Add per-pid idle page tracking using virtual indexing Joel Fernandes (Google)
2019-08-05 17:04 ` [PATCH v4 2/5] [RFC] x86: Add support for idle bit in swap PTE Joel Fernandes (Google)
2019-08-05 17:04 ` [PATCH v4 3/5] [RFC] arm64: " Joel Fernandes (Google)
2019-08-06 8:42 ` Michal Hocko
2019-08-06 10:36 ` Joel Fernandes
2019-08-06 10:47 ` Michal Hocko [this message]
2019-08-06 11:07 ` Minchan Kim
2019-08-06 11:14 ` Michal Hocko
2019-08-06 11:26 ` Joel Fernandes
2019-08-06 11:14 ` Joel Fernandes
2019-08-06 11:57 ` Michal Hocko
2019-08-06 13:43 ` Joel Fernandes
2019-08-06 14:09 ` Michal Hocko
2019-08-06 14:47 ` Minchan Kim
2019-08-06 15:20 ` Joel Fernandes
2019-08-05 17:04 ` [PATCH v4 4/5] page_idle: Drain all LRU pagevec before idle tracking Joel Fernandes (Google)
2019-08-06 8:43 ` Michal Hocko
2019-08-06 10:45 ` Joel Fernandes
2019-08-06 10:51 ` Michal Hocko
2019-08-06 11:19 ` Joel Fernandes
2019-08-06 11:44 ` Michal Hocko
2019-08-06 13:48 ` Joel Fernandes
2019-08-05 17:04 ` [PATCH v4 5/5] doc: Update documentation for page_idle virtual address indexing Joel Fernandes (Google)
2019-08-06 8:56 ` [PATCH v4 1/5] mm/page_idle: Add per-pid idle page tracking using virtual indexing Michal Hocko
2019-08-06 10:47 ` Joel Fernandes
2019-08-06 22:19 ` Andrew Morton
2019-08-07 10:00 ` Joel Fernandes
2019-08-07 20:01 ` Andrew Morton
2019-08-07 20:44 ` Joel Fernandes
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