Re: [External] Re: [PATCH v18 6/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
On Thu, Mar 11, 2021 at 1:16 AM Randy Dunlap wrote: > > On 3/10/21 7:37 AM, Michal Hocko wrote: > > On Mon 08-03-21 18:28:04, Muchun Song wrote: > >> Add a kernel parameter hugetlb_free_vmemmap to enable the feature of > >> freeing unused vmemmap pages associated with each hugetlb page on boot. > >> > >> We disables PMD mapping of vmemmap pages for x86-64 arch when this > >> feature is enabled. Because vmemmap_remap_free() depends on vmemmap > >> being base page mapped. > >> > >> Signed-off-by: Muchun Song > >> Reviewed-by: Oscar Salvador > >> Reviewed-by: Barry Song > >> Reviewed-by: Miaohe Lin > >> Tested-by: Chen Huang > >> Tested-by: Bodeddula Balasubramaniam > >> --- > >> Documentation/admin-guide/kernel-parameters.txt | 14 ++ > >> Documentation/admin-guide/mm/hugetlbpage.rst| 3 +++ > >> arch/x86/mm/init_64.c | 8 ++-- > >> include/linux/hugetlb.h | 19 +++ > >> mm/hugetlb_vmemmap.c| 24 > >> > >> 5 files changed, 66 insertions(+), 2 deletions(-) > >> > >> diff --git a/Documentation/admin-guide/kernel-parameters.txt > >> b/Documentation/admin-guide/kernel-parameters.txt > >> index 04545725f187..de91d54573c4 100644 > >> --- a/Documentation/admin-guide/kernel-parameters.txt > >> +++ b/Documentation/admin-guide/kernel-parameters.txt > >> @@ -1557,6 +1557,20 @@ > >> Documentation/admin-guide/mm/hugetlbpage.rst. > >> Format: size[KMG] > >> > >> +hugetlb_free_vmemmap= > >> +[KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, > >> +this controls freeing unused vmemmap pages associated > >> +with each HugeTLB page. When this option is enabled, > >> +we disable PMD/huge page mapping of vmemmap pages > >> which > >> +increase page table pages. So if a user/sysadmin only > >> +uses a small number of HugeTLB pages (as a percentage > >> +of system memory), they could end up using more memory > >> +with hugetlb_free_vmemmap on as opposed to off. > >> +Format: { on | off (default) } > > > > Please note this is an admin guide and for those this seems overly low > > level. I would use something like the following > > [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP > > enabled. > > Allows heavy hugetlb users to free up some more > > memory (6 * PAGE_SIZE for each 2MB hugetlb > > page). > > This feauture is not free though. Large page > > tables are not use to back vmemmap pages which > >are not used Thanks. > > > can lead to a performance degradation for some > > workloads. Also there will be memory allocation > > required when hugetlb pages are freed from the > > pool which can lead to corner cases under heavy > > memory pressure. > >> + > >> +on: enable the feature > >> +off: disable the feature > >> + > >> hung_task_panic= > >> [KNL] Should the hung task detector generate panics. > >> Format: 0 | 1 > > > -- > ~Randy >
Re: [External] Re: [PATCH v18 6/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
On Wed, Mar 10, 2021 at 11:37 PM Michal Hocko wrote: > > On Mon 08-03-21 18:28:04, Muchun Song wrote: > > Add a kernel parameter hugetlb_free_vmemmap to enable the feature of > > freeing unused vmemmap pages associated with each hugetlb page on boot. > > > > We disables PMD mapping of vmemmap pages for x86-64 arch when this > > feature is enabled. Because vmemmap_remap_free() depends on vmemmap > > being base page mapped. > > > > Signed-off-by: Muchun Song > > Reviewed-by: Oscar Salvador > > Reviewed-by: Barry Song > > Reviewed-by: Miaohe Lin > > Tested-by: Chen Huang > > Tested-by: Bodeddula Balasubramaniam > > --- > > Documentation/admin-guide/kernel-parameters.txt | 14 ++ > > Documentation/admin-guide/mm/hugetlbpage.rst| 3 +++ > > arch/x86/mm/init_64.c | 8 ++-- > > include/linux/hugetlb.h | 19 +++ > > mm/hugetlb_vmemmap.c| 24 > > > > 5 files changed, 66 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt > > b/Documentation/admin-guide/kernel-parameters.txt > > index 04545725f187..de91d54573c4 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -1557,6 +1557,20 @@ > > Documentation/admin-guide/mm/hugetlbpage.rst. > > Format: size[KMG] > > > > + hugetlb_free_vmemmap= > > + [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, > > + this controls freeing unused vmemmap pages associated > > + with each HugeTLB page. When this option is enabled, > > + we disable PMD/huge page mapping of vmemmap pages > > which > > + increase page table pages. So if a user/sysadmin only > > + uses a small number of HugeTLB pages (as a percentage > > + of system memory), they could end up using more memory > > + with hugetlb_free_vmemmap on as opposed to off. > > + Format: { on | off (default) } > > Please note this is an admin guide and for those this seems overly low OK. > level. I would use something like the following > [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP > enabled. > Allows heavy hugetlb users to free up some more > memory (6 * PAGE_SIZE for each 2MB hugetlb > page). > This feauture is not free though. Large page > tables are not use to back vmemmap pages which > can lead to a performance degradation for some > workloads. Also there will be memory allocation > required when hugetlb pages are freed from the > pool which can lead to corner cases under heavy > memory pressure. Very thanks. I will update this. > > + > > + on: enable the feature > > + off: disable the feature > > + > > hung_task_panic= > > [KNL] Should the hung task detector generate panics. > > Format: 0 | 1 > -- > Michal Hocko > SUSE Labs