From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Sandeep Patil <sspatil@google.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>,
joelaf@google.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, Michal Hocko <mhocko@suse.com>,
minchan@kernel.org, namhyung@google.com, paulmck@linux.ibm.com,
Robin Murphy <robin.murphy@arm.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: [PATCH v4 5/5] doc: Update documentation for page_idle virtual address indexing
Date: Mon, 5 Aug 2019 13:04:51 -0400 [thread overview]
Message-ID: <20190805170451.26009-5-joel@joelfernandes.org> (raw)
In-Reply-To: <20190805170451.26009-1-joel@joelfernandes.org>
This patch updates the documentation with the new page_idle tracking
feature which uses virtual address indexing.
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Sandeep Patil <sspatil@google.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
.../admin-guide/mm/idle_page_tracking.rst | 43 ++++++++++++++++---
1 file changed, 36 insertions(+), 7 deletions(-)
diff --git a/Documentation/admin-guide/mm/idle_page_tracking.rst b/Documentation/admin-guide/mm/idle_page_tracking.rst
index df9394fb39c2..9eef32000f5e 100644
--- a/Documentation/admin-guide/mm/idle_page_tracking.rst
+++ b/Documentation/admin-guide/mm/idle_page_tracking.rst
@@ -19,10 +19,14 @@ It is enabled by CONFIG_IDLE_PAGE_TRACKING=y.
User API
========
+There are 2 ways to access the idle page tracking API. One uses physical
+address indexing, another uses a simpler virtual address indexing scheme.
-The idle page tracking API is located at ``/sys/kernel/mm/page_idle``.
-Currently, it consists of the only read-write file,
-``/sys/kernel/mm/page_idle/bitmap``.
+Physical address indexing
+-------------------------
+The idle page tracking API for physical address indexing using page frame
+numbers (PFN) is located at ``/sys/kernel/mm/page_idle``. Currently, it
+consists of the only read-write file, ``/sys/kernel/mm/page_idle/bitmap``.
The file implements a bitmap where each bit corresponds to a memory page. The
bitmap is represented by an array of 8-byte integers, and the page at PFN #i is
@@ -74,6 +78,31 @@ See :ref:`Documentation/admin-guide/mm/pagemap.rst <pagemap>` for more
information about ``/proc/pid/pagemap``, ``/proc/kpageflags``, and
``/proc/kpagecgroup``.
+Virtual address indexing
+------------------------
+The idle page tracking API for virtual address indexing using virtual frame
+numbers (VFN) for a process ``<pid>`` is located at ``/proc/<pid>/page_idle``.
+It is a bitmap that follows the same semantics as
+``/sys/kernel/mm/page_idle/bitmap`` except that it uses virtual instead of
+physical frame numbers.
+
+This idle page tracking API does not deal with PFN so it does not require prior
+lookups of ``pagemap``. This is an advantage on some systems where looking up
+PFN is considered a security issue. Also in some cases, this interface could
+be slightly more reliable to use than physical address indexing, since in
+physical address indexing, address space changes can occur between reading the
+``pagemap`` and reading the ``bitmap``, while in virtual address indexing, the
+process's ``mmap_sem`` is held for the duration of the access.
+
+To estimate the amount of pages that are not used by a workload one should:
+
+ 1. Mark all the workload's pages as idle by setting corresponding bits in
+ ``/proc/<pid>/page_idle``.
+
+ 2. Wait until the workload accesses its working set.
+
+ 3. Read ``/proc/<pid>/page_idle`` and count the number of bits set.
+
.. _impl_details:
Implementation Details
@@ -99,10 +128,10 @@ When a dirty page is written to swap or disk as a result of memory reclaim or
exceeding the dirty memory limit, it is not marked referenced.
The idle memory tracking feature adds a new page flag, the Idle flag. This flag
-is set manually, by writing to ``/sys/kernel/mm/page_idle/bitmap`` (see the
-:ref:`User API <user_api>`
-section), and cleared automatically whenever a page is referenced as defined
-above.
+is set manually, by writing to ``/sys/kernel/mm/page_idle/bitmap`` for physical
+addressing or by writing to ``/proc/<pid>/page_idle`` for virtual
+addressing (see the :ref:`User API <user_api>` section), and cleared
+automatically whenever a page is referenced as defined above.
When a page is marked idle, the Accessed bit must be cleared in all PTEs it is
mapped to, otherwise we will not be able to detect accesses to the page coming
--
2.22.0.770.g0f2c4a37fd-goog
next prev parent reply other threads:[~2019-08-05 17:05 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
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 ` Joel Fernandes (Google) [this message]
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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