| Message ID | 20210816224953.157796-6-mike.kravetz@oracle.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | hugetlb: add demote/split page functionality | expand |
On Mon, 16 Aug 2021 15:49:50 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote: > Describe demote and demote_size interfaces. > > Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> > --- > Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++-- > 1 file changed, 27 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst > index 8abaeb144e44..902059a0257b 100644 > --- a/Documentation/admin-guide/mm/hugetlbpage.rst > +++ b/Documentation/admin-guide/mm/hugetlbpage.rst > @@ -234,8 +234,12 @@ will exist, of the form:: > > hugepages-${size}kB > > -Inside each of these directories, the same set of files will exist:: > +Inside each of these directories, the set of files contained in ``/proc`` > +will exist. In addition, two additional interfaces for demoting huge > +pages will exist:: > > + demote > + demote_size > nr_hugepages > nr_hugepages_mempolicy > nr_overcommit_hugepages > @@ -243,7 +247,28 @@ Inside each of these directories, the same set of files will exist:: > resv_hugepages > surplus_hugepages > > -which function as described above for the default huge page-sized case. > +The demote interfaces provide the ability to split a huge page into > +smaller huge pages. For example, the x86 architecture supports both > +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512 > +2MB huge pages. The demote interfaces are: > + > +demote_size > + is the size of demoted pages. When a page is demoted a corresponding > + number of huge pages of demote_size will be created. For huge pages > + of the smallest supported size (2MB on x86), demote_size will be the > + system page size (PAGE_SIZE). If demote_size is the system page size > + then demoting a page will simply free the huge page. demote_size is > + a read only interface. > + > +demote > + is used to demote a number of huge pages. A user with root privileges > + can write to this file. It may not be possible to demote the > + requested number of huge pages. To determine how many pages were > + actually demoted, compare the value of nr_hugepages before and after > + writing to the demote interface. demote is a write only interface. > + > +The interfaces which are the same as in ``/proc`` function as described > +above for the default huge page-sized case. Are these new demote interfaces duplicated in /proc? Documentation/admin-guide/mm/hugetlbpage.rst says "The ``/proc`` interfaces discussed above have been retained for backwards compatibility.", so new interfaces need not appear in /proc?
On 8/16/21 4:28 PM, Andrew Morton wrote: > On Mon, 16 Aug 2021 15:49:50 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote: > >> Describe demote and demote_size interfaces. >> >> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> >> --- >> Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++-- >> 1 file changed, 27 insertions(+), 2 deletions(-) >> >> diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst >> index 8abaeb144e44..902059a0257b 100644 >> --- a/Documentation/admin-guide/mm/hugetlbpage.rst >> +++ b/Documentation/admin-guide/mm/hugetlbpage.rst >> @@ -234,8 +234,12 @@ will exist, of the form:: >> >> hugepages-${size}kB >> >> -Inside each of these directories, the same set of files will exist:: >> +Inside each of these directories, the set of files contained in ``/proc`` >> +will exist. In addition, two additional interfaces for demoting huge >> +pages will exist:: >> >> + demote >> + demote_size >> nr_hugepages >> nr_hugepages_mempolicy >> nr_overcommit_hugepages >> @@ -243,7 +247,28 @@ Inside each of these directories, the same set of files will exist:: >> resv_hugepages >> surplus_hugepages >> >> -which function as described above for the default huge page-sized case. >> +The demote interfaces provide the ability to split a huge page into >> +smaller huge pages. For example, the x86 architecture supports both >> +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512 >> +2MB huge pages. The demote interfaces are: >> + >> +demote_size >> + is the size of demoted pages. When a page is demoted a corresponding >> + number of huge pages of demote_size will be created. For huge pages >> + of the smallest supported size (2MB on x86), demote_size will be the >> + system page size (PAGE_SIZE). If demote_size is the system page size >> + then demoting a page will simply free the huge page. demote_size is >> + a read only interface. >> + >> +demote >> + is used to demote a number of huge pages. A user with root privileges >> + can write to this file. It may not be possible to demote the >> + requested number of huge pages. To determine how many pages were >> + actually demoted, compare the value of nr_hugepages before and after >> + writing to the demote interface. demote is a write only interface. >> + >> +The interfaces which are the same as in ``/proc`` function as described >> +above for the default huge page-sized case. > > Are these new demote interfaces duplicated in /proc? > Documentation/admin-guide/mm/hugetlbpage.rst says "The ``/proc`` > interfaces discussed above have been retained for backwards > compatibility.", so new interfaces need not appear in /proc? > The new demote interfaces are only in sysfs, they are not /proc.
Mike Kravetz <mike.kravetz@oracle.com> writes: > Describe demote and demote_size interfaces. > > Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> > --- > Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++-- > 1 file changed, 27 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst > index 8abaeb144e44..902059a0257b 100644 > --- a/Documentation/admin-guide/mm/hugetlbpage.rst > +++ b/Documentation/admin-guide/mm/hugetlbpage.rst > @@ -234,8 +234,12 @@ will exist, of the form:: > > hugepages-${size}kB > > -Inside each of these directories, the same set of files will exist:: > +Inside each of these directories, the set of files contained in ``/proc`` > +will exist. In addition, two additional interfaces for demoting huge > +pages will exist:: > > + demote > + demote_size > nr_hugepages > nr_hugepages_mempolicy > nr_overcommit_hugepages > @@ -243,7 +247,28 @@ Inside each of these directories, the same set of files will exist:: > resv_hugepages > surplus_hugepages > > -which function as described above for the default huge page-sized case. > +The demote interfaces provide the ability to split a huge page into > +smaller huge pages. For example, the x86 architecture supports both > +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512 > +2MB huge pages. The demote interfaces are: > + > +demote_size > + is the size of demoted pages. When a page is demoted a corresponding > + number of huge pages of demote_size will be created. For huge pages > + of the smallest supported size (2MB on x86), demote_size will be the > + system page size (PAGE_SIZE). If demote_size is the system page size > + then demoting a page will simply free the huge page. demote_size is > + a read only interface. That is an alternate interface for nr_hugepages. Will it be better to return EINVAL on write to 'demote' file below /sys/kernel/mm/hugepages/hugepages-2048kB ? Or may be not expose demote possibility within 2M hugepage directory at all? > + > +demote > + is used to demote a number of huge pages. A user with root privileges > + can write to this file. It may not be possible to demote the > + requested number of huge pages. To determine how many pages were > + actually demoted, compare the value of nr_hugepages before and after > + writing to the demote interface. demote is a write only interface. > + > +The interfaces which are the same as in ``/proc`` function as described > +above for the default huge page-sized case. > > .. _mem_policy_and_hp_alloc: > > -- > 2.31.1
On 9/21/21 6:52 AM, Aneesh Kumar K.V wrote: > Mike Kravetz <mike.kravetz@oracle.com> writes: > >> Describe demote and demote_size interfaces. >> >> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> >> --- >> Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++-- >> 1 file changed, 27 insertions(+), 2 deletions(-) >> >> diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst >> index 8abaeb144e44..902059a0257b 100644 >> --- a/Documentation/admin-guide/mm/hugetlbpage.rst >> +++ b/Documentation/admin-guide/mm/hugetlbpage.rst >> @@ -234,8 +234,12 @@ will exist, of the form:: >> >> hugepages-${size}kB >> >> -Inside each of these directories, the same set of files will exist:: >> +Inside each of these directories, the set of files contained in ``/proc`` >> +will exist. In addition, two additional interfaces for demoting huge >> +pages will exist:: >> >> + demote >> + demote_size >> nr_hugepages >> nr_hugepages_mempolicy >> nr_overcommit_hugepages >> @@ -243,7 +247,28 @@ Inside each of these directories, the same set of files will exist:: >> resv_hugepages >> surplus_hugepages >> >> -which function as described above for the default huge page-sized case. >> +The demote interfaces provide the ability to split a huge page into >> +smaller huge pages. For example, the x86 architecture supports both >> +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512 >> +2MB huge pages. The demote interfaces are: >> + >> +demote_size >> + is the size of demoted pages. When a page is demoted a corresponding >> + number of huge pages of demote_size will be created. For huge pages >> + of the smallest supported size (2MB on x86), demote_size will be the >> + system page size (PAGE_SIZE). If demote_size is the system page size >> + then demoting a page will simply free the huge page. demote_size is >> + a read only interface. > > That is an alternate interface for nr_hugepages. Will it be better to > return EINVAL on write to 'demote' file below > /sys/kernel/mm/hugepages/hugepages-2048kB ? > > Or may be not expose demote possibility within 2M hugepage directory at all? > Thanks for taking a look Aneesh! You are right. If demote_size is PAGE_SIZE, then demote is just an alternative to freeing huge pages via the nr_hugepages interface. So, why even provide such an interface? It certainly would be easy to just not display demote interfaces for the smallest huge page size. Based on other feedback, I am also making demote_size writable. It makes little sense on x86 with only two huge page sizes. However, it might be useful on other architectures with more sizes. demote_size can only be a valid huge page size. Before your comment, I was going to allow setting demote_size to PAGE_SIZE. Perhaps, that should not be allowed. Thanks for the suggestion, I think removing support for demote_size == PAGE_SIZE will make the code simpler.
diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst index 8abaeb144e44..902059a0257b 100644 --- a/Documentation/admin-guide/mm/hugetlbpage.rst +++ b/Documentation/admin-guide/mm/hugetlbpage.rst @@ -234,8 +234,12 @@ will exist, of the form:: hugepages-${size}kB -Inside each of these directories, the same set of files will exist:: +Inside each of these directories, the set of files contained in ``/proc`` +will exist. In addition, two additional interfaces for demoting huge +pages will exist:: + demote + demote_size nr_hugepages nr_hugepages_mempolicy nr_overcommit_hugepages @@ -243,7 +247,28 @@ Inside each of these directories, the same set of files will exist:: resv_hugepages surplus_hugepages -which function as described above for the default huge page-sized case. +The demote interfaces provide the ability to split a huge page into +smaller huge pages. For example, the x86 architecture supports both +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512 +2MB huge pages. The demote interfaces are: + +demote_size + is the size of demoted pages. When a page is demoted a corresponding + number of huge pages of demote_size will be created. For huge pages + of the smallest supported size (2MB on x86), demote_size will be the + system page size (PAGE_SIZE). If demote_size is the system page size + then demoting a page will simply free the huge page. demote_size is + a read only interface. + +demote + is used to demote a number of huge pages. A user with root privileges + can write to this file. It may not be possible to demote the + requested number of huge pages. To determine how many pages were + actually demoted, compare the value of nr_hugepages before and after + writing to the demote interface. demote is a write only interface. + +The interfaces which are the same as in ``/proc`` function as described +above for the default huge page-sized case. .. _mem_policy_and_hp_alloc:
Describe demote and demote_size interfaces. Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> --- Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-)