| Message ID | 20190726152319.134152-2-joel@joelfernandes.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3,1/2] mm/page_idle: Add per-pid idle page tracking using virtual indexing | expand |
Thanks Joel, just a couple of nits for the doc inline below. Other than that, Reviewed-by: Sandeep Patil <sspatil@google.com> I'll plan on making changes to Android to use this instead of the pagemap + page_idle. I think it will also be considerably faster. On Fri, Jul 26, 2019 at 11:23:19AM -0400, Joel Fernandes (Google) wrote: > This patch updates the documentation with the new page_idle tracking > feature which uses virtual address indexing. > > 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..1eeac78c94a7 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 page > +frame numbers (VFN) 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 need deal with PFN so it does not require s/need// > +prior lookups of ``pagemap`` in order to find if page is idle or not. This is s/in order to find if page is idle or not// > +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 > -- > 2.22.0.709.g102302147b-goog > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >
On Fri, Jul 26, 2019 at 01:17:10PM -0700, sspatil@google.com wrote: > Thanks Joel, just a couple of nits for the doc inline below. Other than that, > > Reviewed-by: Sandeep Patil <sspatil@google.com> Thanks! > I'll plan on making changes to Android to use this instead of the pagemap + > page_idle. I think it will also be considerably faster. Cool, glad to know. > On Fri, Jul 26, 2019 at 11:23:19AM -0400, Joel Fernandes (Google) wrote: > > This patch updates the documentation with the new page_idle tracking > > feature which uses virtual address indexing. > > > > 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..1eeac78c94a7 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 page > > +frame numbers (VFN) 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 need deal with PFN so it does not require > > s/need// > > > +prior lookups of ``pagemap`` in order to find if page is idle or not. This is > > s/in order to find if page is idle or not// Fixed both, thank you! Will send out update soon. thanks, - Joel
On Fri, Jul 26, 2019 at 11:23:19AM -0400, Joel Fernandes (Google) wrote: > This patch updates the documentation with the new page_idle tracking > feature which uses virtual address indexing. > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> One nit below, otherwise Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> > --- > .../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..1eeac78c94a7 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 page > +frame numbers (VFN) 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. Can you please make it more explicit that VFNs are in the <pid>'s address space? > + > +This idle page tracking API does not need deal with PFN so it does not require > +prior lookups of ``pagemap`` in order to find if page is idle or not. 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 > -- > 2.22.0.709.g102302147b-goog >
diff --git a/Documentation/admin-guide/mm/idle_page_tracking.rst b/Documentation/admin-guide/mm/idle_page_tracking.rst index df9394fb39c2..1eeac78c94a7 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 page +frame numbers (VFN) 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 need deal with PFN so it does not require +prior lookups of ``pagemap`` in order to find if page is idle or not. 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
This patch updates the documentation with the new page_idle tracking feature which uses virtual address indexing. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> --- .../admin-guide/mm/idle_page_tracking.rst | 43 ++++++++++++++++--- 1 file changed, 36 insertions(+), 7 deletions(-)